freeze concentration

Presentation on Freeze

Concentration

Prepared by:- Sibo boro (M.Tech)

• Freezing is a process of bringing down the temperatures of food below its

freezing point, and frozen storage generally refers to storage at temperature

below -10°C.

• Freezing results in the transformation of change of state from liquid water

to solid ice.

• Frozen foods can keep much longer than refrigerated foods.

freezing

It is simply a form of melt crystallisation where the water is

crystallised into ice crytals and then the solid ice is separated from the

liquid.

Water is partially frozen to produce an ice crystal slurry in

concentrated product. Separation of ice crystals is then accomplished

using some washing technique. Current applications of freeze

concentration are limited to fruit juices, coffee, and tea extracts, and

beer and wine. Freeze concentration produces a superior product.

Freeze concentration

CRYSTALLIZER

SEPARATOR

A liquid food is cooled with sufficient

agitation. Ice crystals nucleate and grow, and

a slurry of relatively pure ice crystals is

removed. Separation of these pure ice crystals

leaves a concentrated product.

STEPS

Formation of ice crystals of appropriate

number, size, and shape from the feed

product.

Ice crystals are separated from the freeze

concentrated solution, which is the product

concentrate.


process

Feed (F)

Crystal slurry

Ice (I)

Concentrate(P)

When a solid or liquid food is frozen all of its components do not

freeze at once.

First to freeze some of the water which forms ice crystals in the

mixture.

Remaining unfrozen foods becomes higher in solids concentration.

Concentration effect continues as more water is frozen out of the

mixture.

The entire mixture ultimately freezes.

Freezing steps

Equipment involved in


I. A direct freezing system or direct equipment to freeze the liquid food.

II. A mixing vessel to allow the ice- crystal to grow.

III. A separator to remove the crystals from the concentrated solution.

7

Feed

Nucleator

Growth Separation

Ice

Concentrate

Fig: Basic elements in freeze concentration

8

Crystallization starts with Nucleation. Crystallization refers to the formation of solid crystals from a homogeneous solution.

There are two types of nucleation – Primary and Secondary

Primary relates to the birth of the crystal, where a few tens of molecules come together to start some form of ordered structure

Secondary nucleation can only happen if there are some crystals present already. It can occur at a lower level of super-saturation than primary nucleation.

Nucleation

9

• For low super-saturation primary nucleation is not widespread. Secondary nucleation on existing crystals is more likely. Result is small numbers of large crystals.

• For high super-saturation primary nucleation is widespread. This results in many crystals of small size.

• Slow cooling with low super-saturation creates large crystals.

• Fast cooling from high super-saturation creates small crystals.

Supersaturation and Crystal Growth

Freezing-point

depression

Products containing low molecular weight compounds, like sugars and

salts, experience a reduction in freezing point as product is concentrated.

Eg: ICE-CREAM

Adding structure to the ice cream is the formation of the ice crystals. Water freezes out of a solution in its pure form as ice.In a sugar solution such as ice cream, the initial freezing point of the solution is lower than 0° C due to these dissolved sugars (freezing point depression), which is mostly a function of the sugar content of the mix. As ice crystallization begins and water freezes out in its pure form, the concentration of the remaining solution of sugar is increased due to water removal and hence the freezing point is further lowered. This process is shown, schematically.The process of freeze concentration continues to very low temperatures. Even at the typical ice cream serving temperature of -16° C, only about 72% of the water is frozen. The rest remains as a very concentrated sugar solution.

Types of crystallizers

employed in Freeze

concEntration

TYPESDirect Contact:1. Refrigerant expansion

2. Vacuum expansion

Indirect Contact:3. Internal Cooling

4. External Cooling

CHARACTERISTICS

Refrigerant (Freon, butane, CO2) expand directly into liquid.Under vacuum, water vaporizes and cools product below freezing point.

Refrigerant in jacket used to cool product below freezing point.Liquid feed or crystallizer slurry pumped through external heat exchanger to provide freezing.

ICE

CONCENTRATE

WASH COLUMN

RIPENING / GROWTH VESSEL

NUCLEI <50um

FEED

Fig.- Schematic of freeze concentration utilizing a ripening system

SCRAPE SURFACE FREEZER

ICE-Concentrate

separation

Achieved by centrifugation, filtration, wash columns.Wash columns operate by feeding the ice-concentrate slurry into the bottom of a vertical enclosed cylinder. The ice crystals are melted by a heater at the top of the column and some of the melt water drains through the bed of ice crystals to remove entrained concentrate.

WHERE IS FREEZE CONCENTRATION USED?

• The process is specifically used for concentration of

– Heat sensitive substances – All products where maximum retention of product quality is a key

aspect – Where conventional concentration processes cannot be used

APPLICATION OF FREEZE CONCENTRATION :

– Coffee concentration – Citrus Juices – Other fruit juices – Ice beer production – Vinegar Concentration – Fish, meat & vegetable extracts – Wine Application – Beer Application – Dairy Products

.

• Guarantee of aroma and flavour • Higher product value• No aroma recovery required• Environmentally friendly cooling medium • preservation of product properties

Advantages of freeze concentration in compare to any other processing techniques

.

• Hygienic process design with automatic CIP • Time & cost effective• Safe production• Low operating temperature • Prevent microbiological problems

.

• no loss of volatiles or solids• maintains original product characteristics• closed system, prevents oxidation• continuous operation• no need for intermediate cleaning• continuous and stable operation• flexibility in feed composition

• no thermal damage to active components • control of alcohol level • economic storage and distribution • maintain natural freshness

.

Disadvantages

o mushy and unappetizing appearanceo Frozen, prepared foods, like most other prepared foods,

contain unacceptably high levels of sodium that can increase risk of developing high blood pressure and heart disease

o Many vegetables and most fruits lose their crisp texture once frozen, even if you cook them only briefly.

o Cooking frozen corn on the potatoes and broccoli, for example, result in mushy vegetables that taste waterlogged

o Vitamin C and the B vitamins suffer the biggest nutritional losses in frozen fruits and vegetables

.

• Levels of polyphenolic substances, which act as antioxidants to

protect your cells from damage, also are lower in frozen fruits

than fresh•When air comes into contact with frozen foods, it causes freezer

burn and indicates a loss of moisture that affects both texture and flavour

•Food when thawed renders ideal for rapid bacterial multiplication.

When this food is refrozen, it is likely to increase the count of

bacteria causing food poisoning

.

THANK YOU……