uleiuri vegetale 12

8/10/2019 uleiuri vegetale 12

1/74

12Margarine ProcessingPlants and Equipment

Klaus A. Alexandersen

When designing margarine processing plants and choosing the equipment to be

installed, a wide range of considerations have to be made with regard to issues

like actual processing, hygiene, sanitation, and efficiency.

In margarine production, oils and fats usually are considered to be the most

important raw materials used, as oils and fats are significant in relation to

the characteristics of the finished margarine. The type of oils or fats used

has considerable influence on the crystallization characteristics during marga-

rine processing, which has to be considered when choosing the equipment

involved in the margarine processing line. The criteria involved in choosing

this equipment are to a certain extent based on knowledge about product

characteristics, polymorphism, and crystal structure of margarine and related

products.

In this chapter, crystallization of oil and fat products, margarine processing

equipment and packaging methods, processing methods, and specific process flows

are discussed. Various oil types exhibiting interesting crystallization habits are

reviewed along with certain specialized margarine or fat products. Storage of

finished products as well as production quality control and hygiene will also be

covered.

Baileys Industrial Oil and Fat Products, Sixth Edition, Six Volume Set.Edited by Fereidoon Shahidi. Copyright# 2005 John Wiley & Sons, Inc.

459


2/74

1. CRYSTALLIZATION OF OIL AND FAT PRODUCTS

1.1. Product Characteristics

The rheological characteristics offinished margarines are expressed in terms suchas consistency, texture, plasticity, hardness, structure, and spreadability (1).

These characteristics are related to a number of variable factors. These are

temperature, concentration of the disperse phase or solid fat content, crystal size,

crystal size distribution, crystal shape, interparticle forces of van der Waals type

and mechanical treatment (2).

The two dominating factors are the amount of solid triglycerides (or solid fat

index) and the processing conditions during production (3). Formulation or choice

of oil blend allows control of the solid content, which, for identical processingconditions, is directly related to the consistency and type of crystalline structure

formed (35). Processing conditions (rate and degree of cooling, mechanical

working, final product temperature, etc.) regulate the type of crystals formed and

the morphology and extent of intertwining of the solid structure that holds the

liquid oil (6).

The term morphology is used to denote the general relation of the physical

behavior and performance of fats and oils to their crystal structure and the molecu-

lar configuration of their triglyceride components (7).The curve describing the relationship between the solid fat content of a fat and

its hardness is not a straight line. Hardness decreases sharply when solid fat content

goes below a certain value at which the material loses some of the characteristic

plastic properties (2). Haighton (3, 8) has reported the hardness of margarine in

terms of yield value to have a strong correlation to the solid content under constant

processing conditions, as shown in Figure 1.

1.2. Polymorphism and Crystal Structure

It has been reported extensively that fats solidify in more than one crystalline type

(223). Triglycerides exhibit three main crystal typesa;b0, and bwith increas-ing degrees of stability and melting point. The molecular conformations and

packings in the crystal of each polymorph have been reported. In the a form, the

fatty acid chain axes of the triglyceride are randomly oriented and the a form

reveals a freedom of molecular motion with the most loosely packed hexagonal

subcell structure.

The b0 form and the b form are of an extended chain conformation with ortho-

rhombic and triclinic subcell structures, respectively. In the b0 form alternating fatty

acid chain axes are oppositely oriented, whereas in the b form all fatty acid chain

axes are oriented in one way (9, 10).

Crystals of the a form are fragile, transparent platelets approximately 5 mm in

size. They are extremely transitory and require quite low temperatures to exist.

b0 crystals are tiny needles seldom more than 1 mm in length. b crystals are large

460 MARGARINE PROCESSING PLANTS AND EQUIPMENT


3/74

and coarse, approximately 2550 mm in length and can grow to over 100 mm during

extended periods of product storage. Theb form is responsible for product quality

failure in sandy and grainy margarines (7). In severe cases this can lead to

separation of the oil usually described by the term oiling out. Storage temperature

that is too high, inadequate oil blend formulation, or process conditions promote

this product failure.

In the manufacture of margarine, the emulsion is processed in a scraped-surface

heat exchanger that must supercool the melted fat quickly in order to form as many

crystal nuclei as possible (11).

The fat is believed tofirst crystallize in thea form, which is transformed more or

less rapidly to theb0 form depending on the crystal habit of the fat, rate of cooling,

and the amount of mechanical work applied (5, 7, 12, 13).

b0 is the crystal form desired in margarines as it promotes plasticity (4, 5, 13).

The b0 crystal form tends to structure as a fine three-dimensional network capable

Figure 1. Hardness of margarine vs. percentage solid in fat (3). Courtesy of J. Amer. Oil Chem.

Soc.

CRYSTALLIZATION OF OIL AND FAT PRODUCTS 461


4/74

of immobilizing a large amount of liquid oil (6). Large b crystals do not tend to

give a three-dimensional structure.

Both Wiedermann (4) and Thomas (5) have grouped various oils and fats accord-

ing to their crystal habits. As an example, soybean, sunflower seed, corn, coconut,

and peanut oils show a b tendency. Cottonseed oil, palm oil, tallow, and butter oilhave a b0 tendency. Oil blend formulation has a significant influence on the crystal

form attained by a margarine or shortening. The suitability of a fat or oil for

margarine formulation is very much dependent on the crystal size present, amount,

and habit of these crystals (13). Incorporation of a higher meltingb0 tending oil to a

basestock can induce the crystallization of the entire fat into a stable b0 form (5).

The effects of such formulation practice and processing conditions have been

studied extensively by Rivarola et al. (6) for blends of hydrogenated sunflower

seed oil and cottonseed oil. For strong b tending hydrogenated sunflower seedoil, it was found that with increasing cooling rate, the tendency to crystallize in

the b0 form increased. For blends of hydrogenated sunflower seed oil and strong

b0 tending hydrogenated cottonseed oil it was concluded that even at quick cooling

rates, small quantities of the b form are formed.

In certain margarines formulated mainly on hydrogenated oils, such as sunflower

seed oil and canola oil, with very strong b tendency, the problem of sandiness can

be pronounced. Addition of crystal-modifying agents or crystal inhibitors to such

margarines can retard the development of sandiness by delaying the transformationfrom the unstable a form to the stable b form. The addition of sorbitan esters

stabilizes the intermediate b0 form and helps prevent the formation of the b form

(15, 16). Sorbitan tristearate is effective as a crystal inhibitor in margarines. It is

assumed that sorbitan tristearate can be accommodated by the b0 crystal network

of the triglycerides and by stearic hindrance prevent the formation of the more

densely packed b crystal form (17, 18).

In margarine with a good consistency, the fat crystals have formed a three-

dimensional network consisting of primary and secondary bonds. The crystals may

vary in shape and appearance in the form of small needles or platelets with lengths

ranging from less then 0.1 to 20 mm or more (3, 6). They do not behave as indi-

vidual particles and can grow together, forming a strong network (primary bonds).

They may also show a tendency to agglomerate, forming tiny porous crystal

clusters with considerable fewer contact points (secondary bonds) (3). As a result

of this and depending on the resulting crystal form obtained, branched and inter-

twining long chains are formed (6). These chains are responsible for forming

the three-dimensional network. The primary bonds are strong and are not readily

reestablished when broken by mechanical work. Secondary bonds are weak and

readily reestablished when broken by application of mechanical work. As men-

tioned earlier, processing conditions involving fast cooling rates and application

of a certain amount of mechanical work tend to produce margarines with a better

stability and consistency. It is generally accepted that a larger amount of primary

bonds are established if margarine is allowed to crystallize without sufficient degree

of mechanical work. This results in a product exhibiting excessive posthardening

and a hard and brittle texture (19). Due to this, it is advantageous to crystallize



5/74

the product as much as possible in the scraped-surface heat exchanger to achieve

the desired spreadability or consistency.

1.3. Palm OilCrystallization and processing of palm oil with satisfactory results in a scraped-

surface heat exchanger line for margarine and shortening requires some attention

due to the slow crystallization phenomena observed in palm oil.

The polymorphism, crystallization, formulation, and processing of palm oil has

been commented upon and studied extensively (2025, 2634). The slow crystal-

lization of palm oil and the subsequent posthardening phenomenon and product

graininess is a drawback in products formulated with high palm oil contents

and could be a limiting factor to its use (24, 25). It has been shown that the rate-determining step in the crystal growth mechanism of triglycerides is the orientation

of molecules at the crystal faces (20). In palm oil the a-polymorph transformation

to the b0 (i.e., the a lifetime) is unusually long, which is apparently due to the

high level of diglycerides present (approximately 6%) (20, 21). The problem of

posthardening in product formulated with high palm oil contents can be influenced

by choice of proper processing conditions and storage time (2123).

Lefebvre (35) hypothesized that crystals, in general, are formed before or early

in the worker unit (B unit) (see Section 2.3), when a low flow rate is used in ascraped-surface heat exchanger. The important slow processing of the product

leads to a fine crystallization and the destruction of the intercrystal bonds of the

primary type. With a higher flow rate, crystals appear late in the worker unit and

partially during packaging. Crystallization is then coarser and intercrystal bonds

are only slightly damaged, all of which is less favorable.

This hypothesis relates very well with the observations made by Oh et al. (22)

during pilot-plant-scale crystallization and processing of palm oil in a scraped-

surface heat exchanger line for margarine and shortening, as shown in Figure 2.

Palm oil from the same batch was processed with flow rates A andBof, respec-

tively, 28 kg/h and 55 kg/h. Different flow rates result in different retention times

for products A and B in the coolers and the worker unit. Product outlet temperatures

from cooler II of, respectively, 12C and 14C (54F and 57F) were observed.

The outlet temperature from the worker unit were, respectively, 1920C (66

68F) and 2021C (6870F).

Refrigerant temperatures remained constant for both flow rates. Product A

was found to have sufficient time to be more uniformly stabilized before leaving

the process line. Product B was found to have attained insufficient time to be

uniformly stabilized and resulted in a finished product in the quasi-equilibrium

state. Crystal growth in product A was not substantial during 10 days storage at

20C (68F), whereas the crystal growth for product B was significant under

the same storage conditions. It was concluded that better processing conditions

may overcome the problem of slow crystallization of palm oil and also avoid the

effect of posthardening during storage. Different compositions of palm oil and palm

oil fractions give rise to different crystallization behaviors. Hydrogenated palm oil



6/74

has the highest stability in the b0 crystal form followed by palm oil and then palm

stearin.

The preceding observations relate well with observations in industrial-scale

scraped-surface heat exchanger processing lines.

In industrial-scale processing lines, it has been found to be advantageous to

process palm-oil-based industrial margarines with an additional worker unit

installed between the cooling cylinders as shown in Figure 3 (26). This increases

the products retention time in the processing line and allows a slight increase in the

flow rate without compromising the product quality.

Generally, the recommended flow rate for palm-oil-based industrial margarines

is approximately 60% of the nominal capacity of a scraped-surface heat exchanger

process line for industrial margarine (27); for example, a scraped-surface heat

exchanger with a nominal capacity of 3000 kg/h for oil blends based on oils such

as soybean oil or cottonseed oil will, for oil blends based on palm oil, have a

capacity of approximately 1800 kg/h.

In connection with crystallization of palm-oil-based products it should be noted

that the tempering practice for industrial margarines and shortening at 26.7C

(80F) was designed especially for hydrogenated oils. This tempering procedure

tends to generate lower solid fat content at temperatures below 26.7C (80F)

and raise it above 26.7C (80F). It is generally unsuitable for palm oil, palm-kernel

oil, and coconut oil (21).

Figure 2. Schematic diagram of pilot plant (22). Courtesy of The Palm Oil Research Institute of

Malaysia.



7/74

1.4. Canola Oil and Sunflower Seed Oil

We have noted earlier that the crystallization of strongly b tending sunflower seed

oil blends can be influenced favorably toward theb0 polymorph form by addition of

a high melting hardstock of the hydrogenated cottonseed oil (6) as well as by addi-

tion of sorbitan tristearate (17, 18). It should be noted for the formulation and crys-

tallization of margarines based on sunflower seed oil blend that interesterification of

oil blends is a possible route to minimize posthardening. It is possible to produce

table margarine with good consistency and a linoleic acid content of 36% as well as

a trans-isomeric fatty acid content of less then 2% based on an oil blend prepared

by interesterification. Interesterification of a blend consisting of 60% sunflower

seed oil, 15% coconut oil, and 25% hydrogenated sunflower seed oil [melting point

70.7C (159F)] and an iodine value (IV) of 8.5 can achieve this.

Interesterification has been reported to change the crystallization tendencies of

oil blends in such a way that the crystal size in certain interesterified oil blends is

smaller than in the similar noninteresterified oil blends (3639). List et al. (40)

found that interesterification of oil blends made from fully hydrogenated soybean

oil and soybean oil affects the polymorphic transition from the undesirable b form

to the desirable b0 form thus avoiding graininess in finished margarine products.

Interesterification of blends of palm oil fractions is also a possibility in margarine

formulation producing margarines with very low or zero transfatty acid contents

Figure 3. Schematic diagram of industrial source plant.



8/74

(41, 42). With todays health conscious discussions in the media and the use of

transisomeric fatty acid content in margarines as a marketing parameter, the inter-

esterification of oil blends may possibly gain some momentum in the future.

It is well documented that hydrogenated canola oil has a tendency to crystallize

in the b polymorphic form due to its triglyceride homogeneity (it has about 95%of 18-carbon fatty acids) (43). Crystallization of b tending canola oil blends

(low-eururic-acid rapeseed oil) can be influenced by addition of an oil with b0

tending crystallization of different origin. When processing canola-oil-blend-based

margarines for tub or stick packaging, the industry follows a different formula-

tion principle than for sunflower seed oil blends, which are usually used for soft

margarines with high linoleic acid contents. Canola oil constitutes approximately

42% of all vegetable oils consumed in the margarine production in Canada (44),

whereas soybean oil constitutes the majority of all oils supplied for the productionof margarine in the United States (45).

Canola oil contains 5% palmitic acid compared to 11% for soybean oil. Palm oil

contains high levels of palmitic acid, approximately 44%, and it has been found that

the addition of palm oil to canola-oil-based oil blends for margarine production has

a beneficial effect on their polymorphic stability (30). When palm oil is mixed with

canola oil, the homogeneity of the fatty acid chain length is reduced, which pro-

motes b0 crystalline stability (43). Based on the solid fat content found in stick

margarine in North America, it is advantageous to manufacture margarine fromcanola oil by incorporating palm oil at a level of at least 15%, after hydrogenation

of canola oil, or at a level of 10%, before hydrogenation of canola oil. This greatly

delays the polymorphic transition from the b0 to the b form (43, 46, 47). The

amount and point of addition can affect the transition to the b polymorph as hydro-

genation changes the physical properties of an oil blend (46).

The high content of diglycerides (about 6%) in palm oil and the b0 stabilizing

effect of diglycerides probably do not have any significant influence on the poly-

morphic behavior of canola oil blends with palm oil levels as above. The diglycer-

ide content in canola oil blends is only raised slightly by addition of palm oil in the

above levels (46).

It has been found that the b0 stabilizing effect increased with the level of added

palm oil and that this stabilizing effect is most likely due to the decrease in fatty

acid homogeneity and, thus, increased triglyceride diversity (43, 46). This is attri-

buted to the increased range of fatty acid chain lengths, which in turn increases the

irregularity in the crystal network. Increased irregularity in the crystal network

increases the polymorphic stability (46).

A new type of canola oil containing high levels of palmitic acid possesses better

b0 stability in the hydrogenated form (30, 46). The stabilizing effect of palmitic

acid, mentioned by Wiedermann (4), is related to its level in the solid fat fraction,

which is increased by addition of palm oil or when the palm oil is partially hydro-

genated (46). In general, the more diverse the triglyceride structure of the highest

melting portion of the fat, the lower the b forming tendency (48).

To illustrate this, the triglyceride composition of some fully hydrogenated oils

are indicated in Table 1.



9/74

In Table 1, the most b0 stable fat is palm oil hard fat. This may be explained by

its unique composition, and its balanced C48C54 triglyceride content with an

equally balanced C50C52 content (49).

In accordance with the above, it has been found that slightly hydrogenated palm

oil delayed polymorphic transition from b0 tob considerably, compared to no palm

oil addition (43).

Stick margarine of good quality and melting point, 35C (95F), based on a

canola oil blend with palm oil addition, can be produced in a scraped-surface heat

exchanger line for margarine, according to the flow outline in Figure 4. A reduced

flow rate of approximately 85%, compared to the nominal capacity of the scraped-

surface heat exchanger (A unit) (see Section 2.2), is recommended. It should also

be noted that the intermediate worker unit (B unit) (see Section 2.3), with variable-

speed drive inserted between the cooling cylinders, should have a relative volume

of approximately one third of the volume of the intermediate worker unit indicated

in Figure 3, based on a given flow rate and heat exchange area (50).

1.5. Specific Heat and Heat of Fusion

In the solid state, the specific heat of oils and fats shows little change as molecular

weight varies. An increase in specific heat can be observed with increased unsatura-

tion. In the liquid state, specific heat increases slightly with molecular weight but

decreases slightly with less unsaturation. In general, there is little variation among

natural oils and fats (21).

TABLE 1. Percent (%) Triglyceride Composition and Mono- and Diglyceride Content

of Fully Hydrogenated Oils (%).

Hard Fats

Carbon RapeseedNumber Soybean Beef Fata Rapeseed Blend Cottonseed Palm

44 0.2

46 1.4 0.1 0.5

48 0.2 7.5 3.4 0.9 6.4

50 3.3 21.0 1.6 8.8 13.6 40.0

52 27.6 44.9 11.6 15.2 43.5 41.9

54 66.7 24.5 28.3 25.9 40.5 10.7

56 1.7 0.4 6.7 6.2 1.3 0.4

58 0.5 6.8 7.2 60 12.3 9.0

62 31.9 23.6

64 0.8 0.8

Monto 0.4 0.1 0.5 0.5 0.3 0.9

Di 3.6 2.0 3.7 4.4 5.8 8.2

aGlycerides contain odd-numbered and branched fatty acids.

Reprinted from Ref. 49, with permission.



10/74

The specific heats of liquid oils and fats, including palm oil, palm kernel oil, and

coconut oil, may be taken as (21).

Cpkcal=kg 0:47 0:00073 T;

where T is temperature in C (1 Btu/lb 0.252 kcal/kg).A specific heat of 0.514 kcal/kg/C for the fat phase of a retail margarine with

82% fat content and 0.607 kcal/kg/C for the same margarine has been reported (19).

It is difficult to determine the latent crystallization heat in oil blends for

margarine production due to their complexity.

The heat of fusion normally increases with bigger chain lengths and decreasing

unsaturation in the triglycerides. Blends of triglycerides have less latent heat of

crystallization than the similar nonblended triglycerides (19).

Timms (21) has heat of fusion to 17.722.3 kcal/kg for milkfat, 2431 kcal/kg

for fully hardened milkfat, 2629 kcal/kg for cocoa butter in the b0 polymorph,

22.6 kcal/kg for refined, bleached, and deodorized (RBD) palm oil, 29.7 kcal/kg

for RBD palm kernel oil, 26.0 kcal/kg for RBD coconut oil, 31.6 kcal/kg for

fully hardened palm kernel oil, and 31.2 kcal/kg for fully hardened coconut oil.

The heat of fusion is an empirical physical property dependent on the thermal

history or tempering of the oil.

Calvelo (19) has reported the total heat of crystallization (Jc) for a specific retail

margarine with 82% fat content to be 33.4 kcal/kg.

Figure 4. Schematic diagram stick (table) margarine plant.



11/74

2. PROCESSING EQUIPMENT FOR MARGARINEAND RELATED FAT PRODUCTS

Choice of equipment for the processing line is very important for the production of

margarines. For each piece of equipment in the production line, special designfeatures have to be considered for various margarine types to ensure that the

complete processing line has all the necessary capabilities.

Besides the necessary emulsion preparation equipment (see Sections 4.14.3)

such as process tanks, plate heat exchangers, and centrifugal pumps, the essential

equipment for production of margarines is discussed in the following sections.

2.1. High-Pressure Feed Pumps

The margarine emulsion is usually fed from a holding tank to the scraped-surface

heat exchanger (A unit) by a high-pressure positive-displacement pump of the

plunger or piston type with product contact parts in 316 stainless steel. Pumps

with ceramic pistons are available for special applications. Normally, pumps with

two or three plungers or pistons are standard in order to minimize discharge

pressure pulsations in the process line. A high-pressure piston pump for margarine

production is illustrated in Figure 5.To further minimize possible pressure pulsation, the pumps can be installed

together with a pulsation dampener mounted at the discharge. Pulsation dampeners

are air pressurized or spring loaded to ensure a smoother productflow in the process

line. Slow rotational speed of the pumps crankshaft also helps to minimize pressure

pulsation.

The high-pressure pumps are normally supplied with a pressure relief valve and

associated product piping to protect the scraped-surface heat exchanger equipment

downstream and the pump itself, should a blockage of the production line occur.

A filter is normally installed in the suction line to the high-pressure pump to

protect the pump and the hard chromium-plated scraped-surface heat exchanger

cylinder from any foreign matter in the margarine emulsion.

Depending on the designed maximum product pressure of the downstream

scraped-surface heat exchanger and the various types of margarine produced,

high-pressure positive-displacement pumps with maximum discharge pressures of

40 bars (about 600 psi), 70 bars (about 1030 psi), or 120 bars (about 1800 psi) are

normally installed in the process line.

Production of industrial margarine for semiliquid filling does not normally

generate product line pressures as high as, for example, puff pastry margarine.

Gear pumps are normally installed as an alternative to high-pressure positive-

displacement pumps in the production of industrial margarine or shortening for

semiliquid filling (26, 51). Gear pumps for this application normally can deliver

a maximum discharge pressure of 2633 bars (about 390500 psi). The drawback

for the application of gear pumps in margarine processing is that this type of pump

tends to slip at higher discharge pressures (52).

PROCESSING EQUIPMENT FOR MARGARINE 469


12/74

2.2. High-Pressure Scraped-Surface Heat Exchanger

Scraped-surface heat exchanger equipment, specifically designed for margarine

production, is available from Cherry-Burrell Votator Division of Louisville,

Kentucky, United States, Crown Chemtech Ltd. of Reading, U.K., Gerstenberg &

Agger A/S of Copenhagen, Denmark, and Schroeder & Co. (Tetra-Laval owned) of

Luebeck, Germany, under the respective trademarks Votator, Chemetator, Perfector,

and Kombinator.

The scraped-surface heat exchanger (A unit) is the centerpiece of equipment of

the margarine processing line, where initial cooling, supercooling, and subsequent

induced nucleation and crystallization take place (3, 53). The A unit has to have a

high degree offlexibility with regard to variation of process conditions for different

product types and formulations (51, 53).

Figure 5. High-pressure piston pump for margarine production. Courtesy of Schroeder & Co.,

Luebeck, Germany.



13/74

The scraped-surface heat exchanger normally consists of one or more horizontal

heat transfer cylinder assemblies. The cooling cylinder of a cylinder assembly is

usually made from commercially pure nickel or steel, ensuring high heat transfer

coefficients. The cooling cylinder is surrounded by an insulated outer jacket con-

taining refrigerant (normally ammonia or Freon 22). The inside hard chromium-plated surface of the cooling cylinder is continuously scraped clean during

operation by a rotating shaft mounted with free-floating blades. The blades are

thrust against the cylinder wall mainly by the centrifugal force resulting from the

high rotational speed of the shaft. The annular gap between the cylinder wall and

the shaft has been reported to be in ranges from 3 to 22 mm (52), but a more typical

range is 517 mm (3, 5154).

When margarine emulsion passes through the space between the shaft and

cylinder wall, a thin crystallized productfilm is constantly and very rapidly scrapedoff the cylinder wall and remixed with warmer product because of the scraping

action of the blades and the shafts high rotation speed. This causes rapid crystal

nucleation, further emulsification of the product, very high overall heat transfer

coefficients, and a homogeneous cooling of the margarine emulsion under precise

temperature control of the product being crystallized (5355).

The rotational speeds of shafts normally range from 300 to 700 rpm (5153)

and shafts are normally mounted with two, four, or six rows of blades (53).

The blades are fixed to the shafts by specially designed pins and are movableat their fixing points. Figure 6 illustrates the design and operation of a scraped-

surface heat exchanger based on a longitudinal view of the A unit and a cross-

sectional view of the cooling assembly. The shaft is mounted with four rows of

blades in a staggered configuration. The annular gap in this situation varies from

9 to 17 mm.

In the crystallizing product, there is a rapid increase in the solid content during

the passage through the cooling cylinder. Also, the viscosity of the product

increases accordingly with the temperature drop. At a certain point during this

process, a critical shaft speed is reached. Beyond this speed, no additional mixing

is obtained, and the power input required to rotate the shaft at a higher speed will

more than offset any heat transfer benefits resulting from more frequent scraping of

the cylinder wall (54, 55).

In order to prevent buildup of crystallizing product on the shaft, warm water

is normally circulated through the shaft to ensure a clean shaft surface at all times

(5154). The warm water is normally pumped into the shaft at a point near the

thrust/axial bearing assembly and exits close to the water inlet point based on the

inside construction of the shaft (52). The water circulation facility is also beneficial

after a temporary production stoppage, as the warm water helps to melt solidified

product and, thus, facilitates the restart of the A unit.

Energy Balance.The above-mentioned temperature drop, crystal nucleation, and

partial crystallization of the product during the passage through the A unit involve

an overall energy balance including specific and latent heat of the product as well as

other energy source inside the equipment. The power input through the blade shaft

is transferred to the product and the cylinder wall as heat (Qm). A small amount of



14/74

Figure 6. Scraped-surface heat exchanger. Courtesy of Crown Chemtech U.S.A., a division o

472


15/74

heat is also added to the process through the warm water circulation inside the

shaft (Qw).

According to this, the energy in form of heat in the A unit can be expressed as

follows (19):

Qt FCpT1 T2 FJcW2Y Qm Qw; 1

where F is the flow rate, Cp the products specific heat, T1 the emulsions inlet

temperature, T2 the product exit temperature, Jc the latent heat of crystallization

in the fat, W2 the solid fat content at the exit from the A unit, and Ythe fat content

of the margarine emulsion.

In a stationary condition, the heat Qtwill presumably be transferred through the

cylinder wall at an ammonia evaporation temperature ofTf, which makes it possibleto define the heat transfer coefficient U as

Qt UATln; 2

where A is the heat transfer area and T ln is a logarithmic value defined as

Tln T1 lnT1=T2T2; 3

where T1 T1 Tf and T2 T2 Tf.If the product at the exit from the A unit has a solid fat content ofW2 at tempe-

rature T2 and is left to crystallize under stationary conditions, the degree of super-

cooling will be reduced with time, as the crystallization continues until a certain

temperature Ta has been reached. Based on this we have

CpTa T2 JcYWa W2; 4

where Wa is the solid fat content at temperature Ta. Based on sufficient time to

achieve a stable situation,Wa can be determined from the solid fat curve in the pro-

duct at temperature Ta.

From formula (4) the solid fat content at the exit of the A unit, W2, can be

calculated as follows:

W2 Wa

CpT

JcY ; 5

where T Ta T2.Formulas (1), (2), and (5) make it possible to relate process variables such as

theflow rateF, the emulsion temperatureT1, and the ammonia evaporation tempe-

rature Tfwith parameters contributing to the consistency of the margarine such as

the solid fat content at the exit of the A unit W2.

As the crystallization of a fat product demands both a rapid temperature

drop and time for crystal nucleation and crystal growth, sufficient retention



16/74

time for the product in the A unit is required. The retention time can be calculated

from

Tr V=F; 6

where Fis the product flow rate and V is the product volume in the A unit.

Shaft Design. The high viscosity margarine products exhibit during processing

in the A unit increases the significance of factors such as flow rate, shaft rotation

speed, turbulentflow conditions in relation to shaft design, blade configuration, and

annular gap between the shaft and cylinder wall (51). This is due to the viscositys

influence on flow properties, created turbulence, increased effect of mechanical

work, and obtained mixing and heat transfer.

Several shaft or cylinder designs are available today in A units for margarine

processing. The A units can be grouped according to whether they are mounted

with eccentric shafts, oval shafts, sectioned shafts, or oval tubes.

Eccentric shafts have been in wide use in the past and were developed by the

Votator Division of Louisville, Kentucky, and are claimed to provide more intensive

cooling for high-melting bakery margarine as well as a certain amount of working

and compression action similar to that given by the Complector of the older, open-

chill drum system (52) (see Section 5.2).

Figure 7. Votator scraped-surface heat exchanger unit. Courtesy of Cherry-Burrell Votator

Division, Louisville, Ky.



17/74


18/74

The inner line in Figure 9 represents the corresponding thermal layer and shows

the development of the thermal gradient. Again the material outside this layer

remains at a constant temperature above the wall temperatures (i.e., y0 yw). Thethickness of the thermal layers (dT) is given by

dT 2 ax

V 1=2

;

where a is the thermal diffusivity.

Thus the ratio of the thickness of the two layers at any position is solely related

to the Prandtl number of the material:

dn

dT

n

a

1=2 Pr1=2:

For foodstuffs under low shear conditions, the Prandtl number is large, i.e., the

viscous layer is much thicker than the thermal layer.

Within the viscous layer, all the viscous dissipation is taking place. The scale of

viscous heat generation/unit volume (p) at any point is given by

p m du

dy

2;

where du=dy is the velocity gradient.It can be shown that within the viscous layer:

p rV2

4t;

or in coordinates relative to the blade:

p

rV3

4x :

Figure 9. Velocity profile behind the blade (56). Courtesy of N. Hall Taylor, Crown ChemtechLtd., Reading, United Kingdom.



19/74

This result is only true provided the thickness of the viscous layer is less than the

gap width (H); i.e., dn CpyPr1=2

or

V2

>Cpy

k

Cpm

1=2

:

The velocity at which this takes place will decrease as the viscosity increases. In a

margarine process the most critical section is in the final scraped-surface heat

exchanger (SSHE) and then toward the exit end. Here there is the greatest viscosity

(highest Pr) and also the smallest temperature difference between the wall and the

material (y).

In most cases this critical velocity is well above the maximum operating velocity

of the SSHE.



20/74


21/74

This illustrates that the viscous layer is an order of magnitude smaller for the non-

Newtonian material when compared to a corresponding Newtonian material.

The thermal diffusion process, however, is not affected by the shear and so the

same equations as before apply. Thus, the thickness of the thermal layer becomes

closer to that of the viscous layer.This analysis indicates that, for high-melting-point margarines, there is likely to

be a very thin layer close to the cooling surface in which a linear profile is devel-

oped. This is a region of high shear, which effectively lowers the viscosity within

this region. Outside this layer the material is moving uniformly with the rotating

shaft. This condition is often referred to as mass rotation.

There is, however, a number of instabilities that induce vortices, and these can

delay the onset of the mass rotation condition. The next section will discuss the

cause of these instabilities.Flow Instabilities. For clarity, these instabilities will be discussed in terms of

Newtonian fluids, although similar, more complicated behavior will occur with

non-Newtonianfluids.

1. Instability behind the blade.Theflow situation is equivalent to the analysis

of the transition from laminar to turbulent flow along a plate parallel to the

direction offlow and is shown in Figure 10. Instability is predicted to start at

Reynolds numbers greater than 580, although observable disturbances need ahigher value, say 1000.

Thus this type of disturbance will occur when

Re Vx

n >1000:

On the basis of the earlier discussion, this implies a mixing length (L) of

L 1000nV

:

For water n 105 and so ifV 2 m/s, L 5 mm. For an oil of 1000 cP, Lwill be about 5 m, in which case this instability will not be observed since the

distance to the next blade is only 0.2 m.

Figure 10. Instability behind the blade (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd.,

Reading, United Kingdom.



22/74

2. Instability within the annular space.The rotation of thefluid in the annular

space means that a centrifugal pressure gradient exists across the gap, the

higher pressure being at the wall. This pressure gradient is given by

dpdr

rV2

r:

Ignoring the velocity gradients, this implies a pressure difference across

the gap of

p rV2H

R;

where R is the shaft radius.

For our standard SSHE, H 16 mm and R 61 mm so that at 300 rpmp is 0.01 bar, with the pressure at the cylinder wall being slightly higher

than at the shaft surface.

Although the pressure difference seems small compared to the local operat-

ing pressure of say 5070 bars, it is still capable of inducing a circulation

pattern. Thus, by Bernoullis equation, this pressure difference can accelerate

the liquid (ignoring viscous effects) to a velocity u given by

12ru2 p rV

2

HR

;

u

V

2H

R

1=2:

Hence for the standard SSHE, u 1:37 m/s.The significance of this centrifugal effect is that if can cause a series

of fairly stable vortices to be set up between and travel with the blades.Figure 11 shows this effect. This implies that the outer dimension of the vortex

is equal to the gap width H and that the mixing length L lies somewhere

betweenHand 2H. Because this is about a tenth of the distance between the

blades, the heat transfer should be increased by a factor of 23.

Figure 11. Vortices behind the blade (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd.,




23/74

The vortices need some time to establish, and they will be most persistent if

the ratio of the distance between the blade (pR) to the gap width (H) is close

to an integer. For the standard SSHE the ratio is about 13.

3. Enhancement of annular gap instabilities.The instability of the previous

section will be suppressed by higher viscosities, again reverting to mass rota-

tion. There are different methods used to overcome this with varying degrees

of success:

Oval tubes

Oval shafts

Eccentric shafts

Sectioned shafts

The first three are clear from their description. The sectioned shaft equipped

with staggered blades has large flats to accommodate the blades on opposite

sides, so that the gap widths vary between 9 and 17 mm. Figure 12 shows a

diagram of such a shaft. The effect of the staggered blades is that the position

of the flat is rotated through 90 with each successive blade set. This

arrangement has other advantages and will be explained later.

The last three design concepts listed have the common feature that the gap

width at a point on the cooling cylinder will vary as the shaft rotates. In the

case of the oval tube the gap width varies when seen from a point rotating

with the shaft.

Figure 12. Sectioned shaft (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd., Reading,

United Kingdom.



24/74

Figure 13 illustrates this variation in gap width for the case of the oval shaft

and the sectored shaft. An eccentric shaft would also have a sine-type

function but with only one maximum per revolution.

The key feature of these designs is that the change in gap width creates a

radial velocity equal to dH=dtat the shaft surface. This also has the ability togenerate vortices within the gap.

As Figure 14 illustrates, the advantage of the sectored shaft is that it haspulses of much greater velocity than the oval shaft followed by periods in

which the turbulence is allowed to develop.

4. Axial flow. The axial velocity of the material through the annular gap is at a

much lower velocity than the rotational velocity. It can, however, still contri-

bute to the creation of instabilities when the staggered blade configuration

is used. This is because, as the material progresses through the cylinder,

it encounters variations in gap width as illustrated in Figure 15. At each

of the changes in cross-sectional areas there is the possibility to induce

turbulence.

Figure 13. Influence of shaft type on gap width (56). Courtesy of N. Hall Taylor, Crown

Chemtech Ltd., Reading, United Kingdom.

Figure 14. Influence of shaft type on rate of change gap width (56). Courtesy of N. Hall Taylor,

Crown Chemtech Ltd., Reading, United Kingdom.



25/74

Refrigeration System and Scraped-Surface Units. Scraped-surface heat ex-

changers for margarine production are, as mentioned, designed for direct expansion

refrigerants such as ammonia and Freon 22. Advantage is taken of the high rate ofheat transfer due to surface boiling of the refrigerant (54).

A-units with individual refrigeration systems per cooling cylinder assembly

are available from most suppliers. From Figure 16, an A-unit with four cooling

cylinders with individual refrigeration systems can be seen. Each cooling cylinder

is mounted with a surge drum above the cylinder. The surge drum is part of the

refrigeration system of each cylinder. Figure 17 shows how the refrigeration system

of an A-unit cooling cylinder assembly operates.

During normal operation, all stop valves around the A-unit are open. The liquidrefrigerant inlet solenoid valve (A) is open, allowing liquid to pass through the level

control valve (B) and into the bottom of the refrigerant jacket surrounding the

Figure 15. Change of gap with axialflow (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd.,


Figure 16. Chemetator SSHE for margarine processing. Courtesy of Crown Chemtech Ltd.,




26/74

Figure 17. Schematic diagram of refrigeration system. Courtesy of Crown Chemtech U.S.A., a divi

484


27/74

cylinder. Rapid heat transfer through the cooling cylinder wall from the warm

product inside the cylinder causes a considerable proportion of the liquid refrigerant

to vaporize upon contact with the outside wall of the cooling cylinder. Gas and

entrained liquid are discharged from the top of the jacket into the surge drum.

To ensure flooded conditions at all times in the jacket, a liquid level is maintainedin the surge drum by a sensor linked via a capillary tube to the control valve (B).

Gas leaves the surge drum via a pressure regulating valve (C) and the suction

to the suction trap of the fridge plant. The system is controlled by the pilot valve

mounted on the control valve (C). On manual systems, this is adjusted by hand

to give the desired temperature indication on the pressure gauge. On automatic

systems, this is linked via controller to the liquid temperature measuring device

(G) (57).

A current measuring device on the drive motor to the A-unit detects a risegreater than a predetermined level above the normal running current, typically

10%, for the specific product being processed. This automatically closes the liquid

inlet valve (A) and the pressure regulating valve (C) while keeping the A-units

shaft rotating (54, 57). Normally, a warning signal is given to the operator of a

potential freeze-up, which may be prevented if the problem can be identified and

corrected. The system is then reset manually. If the problem is identified, such as

failure of the high-pressure feed pump, it is possible to prevent a certain freeze-up

by operating a hot-gas system either manually or automatically. This system is linedelectrically, so that it will only operate if valves A and C are closed. Selecting the

hot-gas option opens valves E and D. This immediately allows hot gas from the

high-pressure discharge side of the compressor to be introduced directly into

the refrigerant jacket of the A unit. The pressure in the jacket and surge drum rises

and forces all the liquid out via valve D and the suction line into the suction trap of

the refrigeration plant. Once the liquid is ejected, and assuming that the A-unit shaft

is still rotating, the hot-gas system can be switched off manually or automatically

through an electrical time delay relay. The system will then be ready for restart

when the original problem has been corrected.

In certain parts of the world, power cuts can occur frequently and cause problems

in the operation of A units for margarine production. Due to this, A units are usually

mounted with various features in the refrigerant system to minimize the downtime

related to power cuts. The hot-gas option is one feature. At the moment of the

power cut, valves D and E will automatically open and valves A and C will close.

Although the fridge compressor will also stop running, the residual hot gas in

the condenser and pipework will cause an immediate rise in the pressure in the

refrigerant jacket of the A unit. Although the A-unit shaft has stopped rotating,

this should allow it to rotate freely when power is restored. It is, however, import-

ant that this should nevertheless be checked manually after all necessary safety

precautions have been taken by isolating the drive motor locally or at the electrical

control panel (57).

Following a power cut, product feed failure, or any other abnormal conditions,

it is possible that the A unit will be frozen solid. In this situation, the hot-gas system

can be operated, as described, together with the warm water circulation through the



28/74

A-unit shaft to ensure rapid melting of the solidified margarine inside the cooling

cylinder.

Other systems used in A units to help prevent freeze-up situations, as described

above, operate by a drop tank principle, where the refrigerant is removed from

the refrigerant jacket with the aid of increased refrigerant pressure in the systemwithout installation and activation of a hot-gas system.

2.3. Worker Units

Fats require time to crystallize. This time is provided in crystallizers normally

called worker units, or B units. These are cylinders with larger diameters mounted

with pins on the inside of the cylinder walls (stationary pins) and on the rotors

(rotating pins) (3, 54, 55). The pins fixed to the concentric rotor are mounted ina helical arrangement that intermesh with the stationary pins of the cylinder wall

(55). Worker units can be installed either between cooling cylinders of a multi-

cylinder. A unit or after the A unit (3, 4, 51, 54, 55, 58). Worker units have the bene-

fit of giving the margarine emulsion time to crystallize under agitation by the pins

of the rotating rotor (see Section 1).

The worker unit is normally mounted with a heating jacket for tempered water

on the cylinder and often also equipped with its own built-in water heater and

circulation pump for the tempered water. This is advantageous in preventingproduct buildup on the cylinder wall and allows better product temperature control

during the passage through the worker unit. Product temperature increases of 2C or

more due to release of latent heat of crystallization and mechanical work can be

observed in the worker unit (3).

Worker unit cylinders usually have product volumes ranging from 35 L up

to approximately 105 L per cylinder. B units with up to three worker cylinders

mounted on the same support frame are available on the market. Each worker cylin-

der usually has its own individual drive with fixed or variable speed for maximum

flexibility during processing of margarine. The design of a worker unit is illustrated

in Figure 18.

2.4. Resting Tubes

When producing margarine for stick or block wrapping, a resting tube is normally

connected directly to a packaging machine to allow the product sufficient time to

attain a hardness that is suitable for wrapping (3, 4, 54, 55). During production of

table margarine for stick wrapping, the product will commonly pass through the

cooling cylinders of the A unit and a possible intermediate worker unit (B unit)

inserted between the cooling cylinders. From the A unit, the product enters the

resting tube connected directly to the packaging machine (3).

The intermediate worker unit normally has a lesser product volume than final

worker units used in production of soft table margarine for tub filling. The purpose

of limiting the amount of work given to the product isfirst to produce a product that

is not too soft to be handled in the automatic stick wrapping machine. Second, it is



29/74


30/74

Resting tubes for table margarine and similar products are made up offlanged

sections with lengths varying from approximately 450 mm (17.5 in.) to approxi-

mately 900 mm (35 in.) (54, 60). This allows the product volume of the resting

tube to be varied in accordance with the physical characteristics of the solidifying

margarine (54). Resting tubes for table margarine production commonly have dia-meters ranging from approximately 150 to 180 mm (6 to 7 in.) (54, 60). Resting

tubes for production of puff pastry margarine usually have diameters ranging

from approximately 300 to 400 mm (12 to 16 in.). The flanged section in these

resting tubes has a length of up to approximately 1000 mm (39 in.). The volume

of resting tubes for puff pastry margarine is normally considerably larger than

for other products to allow sufficient time for development of the special consis-

tency required in puff pastry margarine (see Section 5.2).

Some equipment suppliers recommend using one single resting tube for feedingtable margarine to the packaging machine, whereas others recommend the use of

two connecting, parallel resting tubes. When one of the two resting tubes has been

filled with product, a motor-actuated rotary valve automatically switches the flow

of product to the second resting tube. The product in the first resting tube remains

static until the second resting tube has been filled.

The construction of a resting tube usually involves the required inlet adaptor,

flanged sections, screens or perforated plates, and an outlet connection flange for

direct linkup to the packaging machine. Alternatively, the resting tube could alsobe mounted with an outlet extrusion nozzle, in case the product is fed to the pack-

aging machine through the older, open hopper system. Resting tubes are normally

jacketed for warm water circulation to minimize the friction between the margarine

and the stainless steel wall of each section. This helps prevent channeling of

the product and reduces the overall discharge pressure required at the high-pressure

feed pump.

Figure 19 shows resting tubes of varied sizes for puff pastry margarine.

2.5. Packaging Equipment

Margarine products are packed in several ways depending on margarine type,

product consistency, and consumer preferences. In the U.S. market, consumer

retail margarines and related products, including butter blends, cover a variety of

products packaged in different ways (61). These can be grouped as follows:

Margarine in quarter-pound sticks

Margarine in one-pound solids

Margarine patties

Soft margarine in tubs

Spreads in quarter-pound sticks or one-pound solids

Soft spreads in tubs

Diet products in sticks or tubs

Liquid margarine in squeeze bottles.



31/74


32/74


33/74

with the wrapper inside to ensure air-freefilling of the product. Product isfilled into

the preformed wrapper bags by the dosing station utilizing a dosing cylinder with a

piston. After subsequent folding and calibrating station, sharp-edged sticks or solids

are transported out of the packaging machine to the cartoning machine. Figure 21

shows an example of a packaging line including the stick wrapping machine and anattached cartoning machine.

This packaging operation is more suitable for softer products than the system

where the product is molded before wrapping (62). Furthermore, the described

system normally operates with a bottom fold principle, which facilitates the folding

and closing operation during wrapping of softer product (64). A more economical

length-side fold principle can also be used in the packaging operation, saving

wrapping material. The two folding principles are shown in Figure 22.

The wrapping materials used in the wrapping operation shown in Figure 20

may be parchment, laminated aluminum foil, plastic-coated material, or plastic

foil (63). For packaging of margarines, the first two wrapping materials are com-

monly used.

Generally, packaging lines as shown in Figure 21 used in the margarine industry

are becoming quite sophisticated, involving electric and electronic monitoring

systems to control the functional sequences of the machinery. Monitoring systems

cover registration of production data, identification of end of wrapping material

roll, product pressure control, photoelectric wrapper registration, and automatic

control of dosing volume by integrated check weigher (63). Computer-aided

machine diagnostic systems can also be installed in packaging machinery. This

involves a programmable logic controller (PLC) monitoring system, which helps

to avoid faults in the packaging operation, to identify reasons for failure, and to

control production data.

High-speed, fully automatic packaging lines for stick wrapping of margarine

with speeds up to 240 sticks per minute are widely used in the U.S. margarine

industry. Such lines include fully automatic cartoning machines for inserting four

Figure 21. Example of a packaging line. Courtesy of Benz & Hilgers GmbH, Neuss, Germany.



34/74


35/74


36/74


37/74

Figure 25. Fully automatic block wrapping machine. Courtesy of C. Bock & Sohn M

495


38/74

and compensator pressure, it is passed on through two laterally placed cylinders via

the resting tube toward the mouthpiece of the block packing machine. Exact weight

control is achieved by the piston stroke of the coupled dosing pistons mounted in

the two cylinders. The extrusion nozzle of the block packing machine is equipped

with a special cutoff device that cuts the product vertically from top to bottom afterfinished dosing. The wrapper is fed from the reel, cut, and positioned automatically

under the extrusion nozzle or mouthpiece. The product block arrives onto the wrap-

per, which is supported by a transport plate. Each wrapper will be controlled in its

final position before dosing takes place. A no-wrapper/no-dosing device is mounted

in the machine. Vacuum will hold the wrapper correctly on the transport plate while

the block moves toward the folding level. Here the prefolded block will be trans-

ported by a chain conveyor to the various folding stations. The wrapped and folded

block leaves the machine on a transport belt (69).Modern sheet wrapping production lines function after the same principles

except that the product is extruded as a sheet or plate from the mouthpiece verti-

cally into a plate turner. Before the extrusion, the wrapper is positioned and follows

the product into the plate turner. The plate turner is driven by a four-step gear drive

rotating the plate turner 90 while the cross-folding takes place between each dos-

ing/extrusion cycle. In a horizontal position the plate is pushed out on a conveyor

belt and transported through a permanent folding device for end folding below the

wrapped plate (70).

2.6. Refrigeration Plants

Refrigeration is a key operation in the margarine production plant. In the margarine

industry, Freon 22 and ammonia were widely used as refrigerants. New regulations

phasing out the use of chlorofluorocarbons (CFCs) are in place in many countries

for environmental reasons (see Section 3). Plans for phasing out a hydrochloro-

fluorocarbon (HCFC) such as Freon 22 (R-22) are currently being made or in

some countries are already in place (52, 71). The layout of an ammonia compressor

plant servicing an SSHE for margarine production can be seen in Figure 17 (see

Section 2.2).

Ammonia systems consist of a compressor designed to compress the low-

pressure ammonia gas from the SSHE. The gas is then discharged from the

compressor into the condenser. When ammonia is under a pressure of 150 psi

(10 bar), it will liquify at a temperature of 25.6C (78F) (71). Condensers can

be of the air-cooled or water-cooled type covering also evaporative condensers

(72). From the condenser, the liquid ammonia flows to the receiver. The receiver

in which the high-pressure ammonia liquid is stored maintains a constant supply

of refrigerant to the SSHE.

Figure 26 shows a packaged ammonia compressor system designed for servicing

an SSHE in margarine production. The system is skid-mounted from the factory for

easy installation. Only the condenser of the system is supplied loose.

Ammonia compressor systems used in margarine plants are usually equipped

with highly efficient superseparators for removal of lubrication oil from the



39/74

ammonia (71). Lubrication oil carried over into the ammonia will eventually reduce

the heat transfer efficiency of the SSHE, as the oil will be deposited as a thin film on

the outside wall of the cooling cylinder. This can reduce the heat transfer consider-

ably. Compressors of the reciprocating piston type or screw compressors are nor-mally installed depending on compressor cost at various capacities or individual

preferences (71). The screw compressors, with their highly efficient coalescing

separators, reduce the amount of oil in the system considerably (70).

The use of ammonia as a refrigerant in margarine plants offers certain advan-

tages as well as disadvantages. The advantages are cost, efficiency, detection, and

environment (70). The quantity of refrigerant needed to charge an ammonia system

is substantially less than for other systems, which provides additional savings.

Ammonia is the most efficient of the commonly used refrigerants. Easy detect-

ability of ammonia leaks is an advantage compared to R-22, taking into consi-

deration the latest enforcement laws by the U.S. Environmental Protection

Agency (EPA). Finally, ammonia is biodegradable and has no impact on the ozone

layer (71).

The disadvantage are toxicity and flammability. Ammonia has a corrosive effect

on tissues and can cause laryngeal, bronchial spasm and edema, which lead to

obstructed breathing. Ammonias flammability range in air is 1625% by volume.

It is usually characterized as hard to ignite (71). A suitable ammonia detection

system with alarm should be installed and well maintained. Detectors should sound

an alarm at the lowest practical level, not to exceed 1000 ppm.

Due to the disadvantages of ammonia, a number of regulations and standards

provide safe practice procedures for the use of ammonia as a refrigerant. Details on

mechanical requirements of refrigeration systems can be found in ANSI/ASHRAE

Standard 15, Safety Code for Mechanical Refrigeration. Piping requirements

should comply with ANSI B31.5, Refrigeration Piping (70). Many local and

national codes must also be complied with in many states.

Figure 26. Packaged ammonia compressor system. Courtesy of Cremeria Americana SA,

Mexico.



40/74


41/74

HFCs, FCs, and other fluoro-based compounds are some of the alternatives to

HCFCs and CFCs (75).

4. PLANT LAYOUT AND PROCESS FLOWSHEET

In margarine production, raw materials account for about 50% of the margarine

cost, actual production costs account for 20%, and other costs are 30% of the total

(35). Well-managed formulation and efficient, accurate metering/weighing systems

for the various raw materials in the emulsion preparation plant are essential factors

for cost-efficient margarine production (35, 7678).

Table 2 can be used to illustrate the significance of the cost of the various ingre-

dients in a specific recipe for production of 1 ton of margarine.Microcomputers, allow the optimizing of formulation cost or least-cost formula-

tion. One method is to select from the formula file according tofluctuations in raw

materials prices. The high number of formulas required can make this task quite

difficult unless computers are used to sort out the least-cost formula. Production

schedules and previous purchases of raw materials will also have to be considered

(35).

Another method is to create new formulations by minimization. Here formula

cost is optimized against constraints. These constraints are based on finished pro-duct characteristics in relation to raw material characteristics. Production cons-

traints relate to raw material properties, existing and new processes as well as

productivity in the plant. It is essential to compare formulas and processes in order

to optimize productivity by minimizing metering or weighing errors during emulsion

TABLE 2. Ingredient Cost (79).

U.S.

Ingredient % in Recipe $/Ton Margarine

Soybean oil, hydr. 44/46C 32.00 190.30

(111.2/114.8F)

Soybean oil, hydr. 34/36C 4.00 23.79

(93.2/96.8F)Soybean oil 44.00 213.22

Emulsifier 0.20 5.98

Lecithin 0.20 1.61Color (carotene) 0.005 12.65

Aroma 0.02 8.05Water 16.935 0.14

Salt 2.00 3.91

Milkpowder 0.50 23.00

Potassium sorbate 0.10 8.40Citric acid 0.04 2.53

100.0 493.58

From Crown Wurster & Sanger, Minneapolis, Minnesota, with permission.

PLANT LAYOUT AND PROCESS FLOWSHEET 499


42/74


43/74


44/74


45/74


46/74

materials consumption and inventory reporting, maintenance in relation to equip-

ment operational hours, optimization of process in relation records of energy

consumption, quality assurance, and total plant supervision (84).

The possibilities for automation are quite extensive. For each margarine produc-

tion plant different levels of automation may be required or possible. The automa-tion level for a plant is decided and planned according to factors such as (84):

Selected or installed process equipment and its affect on automation level

Requirements with regard to level of operator interactions and labor

Required degree of reporting within the plant in relation to quality control,

inventory control, and accounting

Examples of automation in margarine production have been reported (7678).

Automation based on the use of scale tanks for automatic batching has been

reported in detail for a U.S.-based plant for production of margarine and blends

containing butter (77).

Oils required for the margarine production in the described plant may arrive by

railroad tank car or road tank truck and are unloaded by connecting the vessels

discharge system to the receiving pump of the plant. A sanitary flowmeter registers

the amount of product received and transmits this information to the processingcomputer for inventory control. Storage tanks for the received oils are normally

of the stainless steel silo type. The tanks are equipped with both heating and cooling

controls for maintaining a constant oil temperature and are flooded with nitrogen to

prevent oxidation of the oils. Oils are pumped from the storage tanks to the batching

system in hot-water heated jacketed pipelines to keep the oils from solidifying (77).

Oil storage tanks could be mounted with level controls capable of reporting the oil

level in each storage tank to the processing computer. In this way the computer can

monitor whether the oil level in a storage tank is large enough to meet the batch

requirements.

Milk required for the production is received in a similar manner and pasteurized

before storage in a refrigerated tank until required for batching. A portion of the

milk may be used for combining with salt for brine milk.

Minor ingredients such as sodium benzoate, potassium sorbate, citric acid,

cream, emulsifier, and butter are stored in individual, stainless steel tanks. Each

of these ingredients are weighed, during the batch formulation, in a smaller stain-

less steel tank suspended from an electronic loadcell (77). Microingredients such

as vitamin A, vitamin D, carotene, color, andflavor are also stored in stainless steel

tanks and enter the system through piston-type metering pumps. The batching

system consists of two larger stainless steel tanks suspended from an electronic

loadcell and are used for weighing the oils and the milk ingredients.

Through a keyboard, the computer operator can enter the formulas and number

of batches required for the production each day. The computer can hold numerous

formulas. A sequential weighing of each ingredient designated by the formula used

is started by computer command. The ingredients weighed are discharged into one



47/74


48/74

Figure 28. Flowmeter-based emulsion preparation. Courtesy of Crown Chemtech U.S.A., a divisi

506


49/74

Individual oil feed lines and flowmeters for each oil type can be installed for

optimal accuracy. When metering of all oil types for the oil blend is completed,

the operator enters the desired quantity of emulsifier solution into a second batch

controller. The sequence is repeated, but this time for metering the emulsifier

solution, which has been pre-prepared in designated tanks. The same sequence isfinally repeated for the prepared watermilk phase through a third batch controller

and flowmeter after a proper period of time, allowing sufficient mixing of the oil

blend and emulsifier solution in the blending tank.

The watermilk phase preparation system in Figure 28 is based on the use of a

batch mixing and pasteurization tank. A defined quantity of water is added to the

batching tank. Milk powder is added to the tank and mixed with the water during

heating. The tank is equipped with a special agitator designed to prevent burning of

protein on the tank wall. Heating and cooling of the prepared batch takes placein the tank by steam heating of the jacket of the tank. When the desired temperature

of 7578C (167172F) has been reached, heating is stopped and cooling is

commenced by circulating chilled water through the heating/cooling jacket of the

tank. Figure 29 illustrates the described batch mixing and pasteurization tank.

The pasteurized batch is transferred to a holding tank for use in the emulsion

preparation. The process of mixing and pasteurization of a batch takes less than

2 h (84). The watermilk phase can alternatively be prepared in a mixing tank

and pasteurized using a modern type of multisection plate pasteurizer. The prepared

Figure 29. Batch mixing and pasteurization tank. Courtesy of Crown Chemtech U.S.A.,

a division of Crown Iron Works Co., Minneapolis, Minnesota.

PLANT LAYOUT AND PROCESS FLOWSHEET 507


50/74

watermilk phase is pumped from the mixing tank to the plate pasteurizer, where

the product undergoes successive stages of treatment such as preheating, heating

to 7578C (167172F), holding at that temperature for 1520 s, cooling, and

chilling in a continuous flow. The preheating and cooling stages are combined in

a regenerative section where the outgoing pasteurized product gives up its heatto the incoming product. This greatly reduces the thermal energy demand (84).

Figure 30 illustrates a possible layout of the equipment of the margarine proces-

sing line shown in the flow diagram in Figure 28.

Pasteurization of the watermilk phase is a very important process. The pasteur-

ization kills microorganisms that cause disease. If infections occur, the reason is

either that heat treatment has not been properly performed or that the watermilk

phase has been reinfected after pasteurization (84). Due to this it is important to

monitor the pasteurization process carefully in order to make sure that the watermilk phase is treated in the prescribed manner. Proper storage conditions for the

pasteurized batch before use in the emulsion preparation are also important.

Pasteurization of the complete margarine emulsion as shown in Figure 27 is often

done to minimize the risk of reinfection and to ensure the best possible storage

properties of the finished margarine product.

Thorough cleaning and disinfection of the equipment are essential parts of

margarine operations to ensure optimal hygienic conditions. Combined with proper

processing such as pasteurization, proper cleaning procedures help to ensureoptimal product shelf life.

Extensive development has and is taking place in the area of cleaning and

disinfection techniques. A wide range of detergents and disinfectants is available

today, complicating the choice of suitable cleaning agents for particular food pro-

cessing operation. Economic pressures have speeded up the mechanization and

automation of the cleaning operations.

The degree of cleanness can be defined by the following terms (84):

Physical cleanness: removal of all visible dirt from the cleaned surfaces.

Chemical cleanness: removal of all visible dirt as well as microscopic residues,

which can be detected by taste or smell but are not visible to the naked eye.

Bacteriological cleanness: obtained by disinfection that kills all pathogenic

bacteria and most, but not all, other bacteria.

Sterility: destruction of all microorganisms.

Even today, some items of equipment in the margarine production can be found

not to be designed for easy cleaning and draining. Tanks with flat bottoms and

inadequate drainage points can be found. Pipes are found with unnecessary bends,

blank ends, and unsatisfactory valves. Such installations are very difficult to clean

and could lead to the buildup of stagnant products.

During the design and erection phase of new plants, full consideration should be

given to problems of cleaning. Cleaning operations must be performed strictly

according to a carefully planned procedure in order to achieve the required degree



51/74

Figure 30. Layout of a margarine processing line. Courtesy of Crown Chemtech U.S.A., a divisio

509


52/74

of cleanness. The cleaning cycle in a margarine operation usually comprises the

following steps (84, 85):

Removal of residual fat and milk solids in the plant by means of drainage and

forcing product out with water or compressed air.Preliminary wash with warm water about 49C (120F) for loosening fat and

milk solids adhering to the sides of the equipment.

Cleaning with alkaline detergent solution at 6070C (140 158F) for approxi-

mately 30 min to remove all traces of fat, milk solids, and other residues from

the interior of the production line. All blank ends and valves not suitable for

CIP should be removed and washed by hand.

Postrinsing with clean, warm water to remove the last traces of detergent.

Disinfection by means of heating with steam or hot water, alternatively disinfec-

ting with chemical agents such as chlorine and other halogen compounds,

benzoic acid washing, or quaternary ammonium salts. In the latter case, the

cycle is concluded with a final rinse.

Cleaning in place (CIP) can be defined as circulation of cleaning liquids through

machines and other equipment in a cleaning circuit (84). This method of cleaning

has replaced the older practice of stripping down valves and other difficult to clean

equipment in many margarine factories. The CIP method is essentially the same as

the method described above (85).

The passage of the high-velocity flow of liquids over the equipment surfaces

generates a mechanical scouring effect that dislodges dirt deposits. This only

applies to the flow in pipes, heat exchangers, pumps and valves, etc. The usual technique

for cleaning of tanks is to spray the detergent on the upper surfaces and allow it to

run down the walls. The mechanical scouring effect is often insufficient but can to

some extent be improved by the use of specially designed spray nozzles or cleaning

turbines. Tank cleaning requires large volumes of detergent that must be circulated

rapidly (84).

4.4. Storage of Finished Product

Storage conditions play quite an important role for the overall quality of margarine

products. Insufficient or improper storage conditions can lead to several product

failures such as sandiness or graininess, oiling out, lack of plasticity, brittleness,

or microbiological spoilage for sensitive product types (86).

Margarines are usually stored in palletized cartons or boxes in refrigerated

storage rooms built with insulated walls and insulated ceiling for optimal energy

utilization. The margarine pallets are usually placed individually in a rack system

to allow for proper air circulation around each pallet. During the initial period of

storage, the temperature change in the product is not uniform across the pallet load.

The cartons or boxes on the outer layers reach storage temperatures well before

those in the middle of the pallet (52). This could lead to differences in product

structure depending on whether the product is located in the outer layer or in the

middle of the pallet.



53/74


54/74


55/74

Formulation. Several patents have been issued covering low-fat spreads formu-

lation and processing indicating that critical process control and/or significant levels

of water binding agents are required (91, 92, 97, 98).

From a formulation point of view, low-fat spreads can be grouped as follows:

Without protein and without stabilizer added

Without protein but with stabilizer added

With low protein level and with stabilizer added

With high protein level and with stabilizer added

With low protein level and with stabilizer and thickener (fat replacer) added

To further illustrate and summarize the complexity of low-fat spreads formula-tion and possible ingredients to be used, a typical formulation of a 40% fat content

low-fat spread is shown in Table 4 of functional properties of possible ingredients in

TABLE 4. Low-Fat Spread at 40% FatTypical Formulation.

Component Ingredients %

Oil blend Hydrogenated vegetable oil 37

40Vegetable oil

Emulsifier Mono and diglycerides 0.251.0

Lecithin

Polyglycerol ester

Color Beta carotene including vitamins A and D 0.0010.005

Annatto

Flavor Butter extract 100200 ppm

Organic acids

Ketones

EstersStabilizer Maltodextrin 13

Gelatin

Modified starch

Sodium alginate

Preservative Potassium sorbate 0.10.3Sorbic acid

Water with protein source Buttermilk 5060

Skim milk

Whey

Caseinate

Soy

Salt Salt 12

Starter culture S. Cremoris Trace

S. Diacetylactis

S. Leuconostoc

Sodium-hydroxide 0.1

Sodium-hydrogen Acid regulator 0.10.4

Trisodium-citrate Acid regulator 0.10.4

Buffer

PROCESSING OF LOW-FAT SPREADS, PUFF PASTRY MARGARINE 513


56/74


57/74


58/74

Figure 31. Schematic diagram of SSHE process line for production of low-fat spreads. Courtesy of Cro

Minneapolis, Minnesota.

516


59/74

crystallization takes place. This is necessary to ensure a homogeneous product and a

fine dispersion of the aqueous phase. The use of emulsifiers gives greater numbers

of smaller water droplets in the product, resulting in a light texture and good flavor

release.

Milk proteins and soy lecithin can also affect the water droplet size. Proteins andlecithin tend to increase the drop size (91, 100).

The aqueous phase is prepared in a separate vessel and would typically comprise

skimmed milk, whey, or water. Salt and various acidity regulators are added to the

water phase along with an adjustment of the acidity. Finally, a bulking agent is

added to yield the optimum viscosity for a particular formulation.

The influence of the viscosity and functionality of the aqueous phase on emul-

sion stability, spreading, and eating characteristics of the product are significant. In

high-protein low-fat spreads, the proteins function is to create a three-dimensionalnetwork responsible for immobilizing the water (94). The functional properties

for a given protein are greatly influenced by the environment (i.e., other ingredients

such as stabilizers) in which the protein is present during the emulsification

process (101).

The heated aqueous phase is added to the oil phase under controlled conditions

creating a good-quality water-in-oil emulsion. Critical parameters at this stage

include the temperature of the two phases, water phase viscosity and functionality,

addition rate, and type and speed of mixing.The prepared emulsion is fed via a balance tank to a high-pressure pump, usually

of a piston variety to a series of in-line SSHEs. Once in the pasteurizer heating

cylinders, the product is pasteurized and held prior to being subjected to precooling

and prepared for crystallization. Cooling, stabilizing, and texturizing of the emul-

sion are continuously undertaken within a series of A and B units.

The emulsion is rapidly supercooled with vigorous agitation by the scraping and

blending action of the knife blades of the A unit. During the passage through the A

unit, a thinfilm of crystallized emulsion is continuously scraped off the walls of the

cooling cylinders and mixed with warmer emulsion. The water droplet size is re-

duced further during this step and the reduction is dependent on emulsion viscosity,

shaft speed, and retention time. The process continues until the emulsion leaves

the last cylinder and enters a worker unit for final texturization. Due to the presence

of higher amounts of solidified fat in the product during its passage through the

worker unit, water droplets can recoalesce during this process step. Typical process

conditions (2540% fat) would be as follows (90): aqueous phase temperature

45C (113F), oil phase temperature 60C (140F), emulsion temperature 52C

(125.6F), pasteurization temperature 85C (185F) for 15 s, precool temperature

40C (104F), final cooling temperature 12C (57.6F), temperature at filler 16C

(60.8F).

Ammonia/Freon evaporation temperatures would vary depending on throughput.

For stick wrapping, the produced product passes to a resting tube connected

directly to the stick wrapping machine. When the product is filled into tubs, it

is conveyed directly from the after-treatment worker cylinder to the filling

machine.

PROCESSING OF LOW-FAT SPREADS, PUFF PASTRY MARGARINE 517


60/74

Excess product from the packaging operation is continuously remelted in a

rework SSHE in a controlled manner and returned to the system via the balance

tank or a positive pump facility for adding reclaimed material.

Figure 32 illustrates and summarizes the basic process lines used for the produc-

tion of different types of low-fat spreads.

Figure 32. Basic process line for low-fat spreads (91). (a) Conventional processing;

(b) inversion processing; (c) method of oil in water spreads.



61/74

Figure 33 shows an SSHE with four cooling cylinders, one pin wor

uleiuri vegetale 12

Documents