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World Journal of Science and Technology | www.worldjournalofscience.com | 2011 | 1(7): 32-38

World Journal of Science and Technology 2011, 1(7): 32-38 ISSN: 2231 2587

EFFECTS OF WET PROCESSING METHODS AND SUBSEQUENT SOAKING OF COFFEE

UNDER DIFFERENT ORGANIC ACIDS ON CUP QUALITY

Kulandaivelu Velmourougane

Post Harvest Technology Laboratory

Coffee Research Sub Station, Chettalli- 571 248, Coorg, Karnataka, India

Corresponding author e-mail: [email protected]

Abstract

Effects of soaking wet parchment coffee processed by three different demucilization methods (Natural fermentation

followed by manual wash, Enzyme treatment followed by machine wash and Machine wash alone) under different

organic acids viz., Citric, Lactic, Malic, Phosphoric and Ascorbic acids was studied at two concentrations of 0.0001

M and 0.001 M. Coffee processed by natural fermentation + manual wash + acid soaking had good body, fair

acidity and slight bitter/medicinal taste. The added cost involved in use of acids for soaking wet parchment

equivalent to a tonne of clean coffee at the conc. of 0.0001 M was found to be Rs.10/-, 10/-, 15/-, 20/- and 98/- for

malic, phosphoric, lactic, citric and ascorbic acid respectively.

Keywords: Coffee quality, Organic acids, Post wash soaking

Introduction

Under the present liberalized system of

coffee marketing in India, growers are directly selling their produce in the domestic and export market. As a result, traders and exporters are buying their requirements directly from the farm gate. The quality of coffee will be the main stay in the trade especially when the coffee is a surplus commodity and when the coffee prices are at low. In coffee the main indices of acceptability include raw (moisture, size, colour, presence of defects, foreign matter etc.,), roast bean visual characteristics and cup or liquor quality (body, acidity and aroma) attributes. Processing is a major activity in coffee production chain and the most important from a quality point of view. Coffee processing involves series of stages each of which has a distinct purpose. There are basically two methods of coffee processing which differs in complexity and the resultant raw coffee differs in quality characteristics. These are; the wet method by which plantation or parchment coffee is produced and the dry method by which natural or cherry coffee is

produced. Dry processing is primarily used to produce coffee of rich body and aroma and wet processing for fine aroma and acidity (Viani, 2000).

In wet processing, underwater soaking is one of the important step followed in quality coffee production in India. Under-water soaking is nothing but complete immersion of washed parchment under clean water for specific time. To soak about 2700 kg wet parchment equivalent to 1 tonne of clean coffee, around 2000L clean water is required. Under-water soaking of washed wet parchment for specified period was reported to improve raw and liquor quality of coffee by way of leaching some of the chemical compounds (diterpenes, poly phenols, tannins etc.) responsible for bitterness and browning of coffee beans. It was reported that parchment soaked under basic conditions give dull parchment whereas it is very clean when soaked under acidic conditions. The process of dry fermentation of parchment followed by underwater soaking is popularly called the Two stage fermentation procedure and is widely followed in Kenya (Mburu, 1999). Wootton (1963) and Northmore (1965a) reported improvement in coffee quality by


post-fermentation soaking in 1% sodium bisulphite and sodium metabisulphite solutions respectively. Improvement of quality has also been observed by under-water soaking for 24 hours (Wootton, 1963; Brownbridge, 1966)

In recent time studies have revealed that presence of some acids (Phosphoric, Quinic, Lactic, Citric, Acetic, Malic etc.,) impart specific acidity to the final cup of coffee, the presence and absence of these acids may contribute unique flavours, aroma and sparkle to the brew of high grown coffees. Acidity is a sharp and pleasing taste, as opposite to sour taste, which may indicate signs of fermentation and best appreciated in a low roasted filter coffee (Viani, 2000). Malic, citric, tartaric, lactic, acetic, phosphoric and cholorogenic acids are the compounds which contributes to overall acidity and give a brew its particular identity (Terry Mabbett, 1999). To test this hypothesis, a study was undertaken in arabica coffee to determine the improvement if any, in quality of coffee by way of post wash soaking in different organic acid solutions. This is the first report on use of organic acids for soaking coffee beans for quality improvement.

Materials and Methods

For soaking experiments, the pulped coffee beans were obtained by pulping the arabica fruits from Coffee Research Sub Station, Chettalli. Three different demucilisation methods namely a) Natural fermentation followed by machine wash, b) enzymatic fermentation (Coffenz, (Pectinolytic enzyme) @ 0.16 g/kg fruits) followed by machine wash and c) direct machine wash (Aqua pulper) was followed.

The washed wet parchments (25 kgs/treatment) were soaked in five different organic acids viz; Citric, Malic, Lactic, Phosphoric and Ascorbic acids at the concentrations of 0.0001 M and 0.001 M in triplicates for 12 hours. The customary underwater soaking and parchment without soaking were maintained as control 1 and 2 respectively. After soaking the parchments were dried in conventional manner on tiled floor till the desired moisture level (10.0-10.5%) was reached. The dried coffees were peeled, cleaned and sent for cup quality evaluation. All the samples were subjected to comprehensive quality assessment at the Quality evaluation Department, Coffee Board, Bangalore.

Coffee cup quality evaluation

After the completion of drying, the coffee bean samples were hulled in a mechanical huller, cleaned, graded, and packed. Further, all the experimental coffee samples were sent to Coffee quality evaluation centre, Bangalore, India, where the quality was evaluated based on the physical and cup quality attributes. Cup quality was assessed by experienced and professional coffee tasters (35 numbers). The cup quality was evaluated based on Hedonic scale with rating from 1 to 6 (6, good; 5, above average; 4, average; 3, below average; 2, falling off; 1, poor). These ratings are a measure of cup quality such as acidity, body, and aroma or flavor. The rating presented in the current study is based on the coffee quality evaluation generally employed for marketing purposes in India and elsewhere.

The details of numerical points awarded for quality of coffee are furnished below.

Raw Score Roast Score Liquor Score

Bluish 5 Fine 5 Good 6

Greyish blue 4 Good 4 Fair average quality + 5

Greyish green 3 Fair to Good 3 Fair average quality 4

Greenish 2 Fair 2 Below Fair average quality 3

Brownish 1 Poor 1 Falling off 2

Poor 1

Results and Discussion Effects of natural fermentation + manual washing on coffee quality subjected to acid soaking

Data on cup quality of coffee processed by natural fermentation followed by manual wash and acid soaking are presented in Table1. Wet parchment

soaked under citric and lactic acids at the conc. of 0.0001 M have better result on quality compared to other treatments. This was followed by malic, phosphoric, ascorbic acids, under-water soaking and Control (no soaking) in decreasing order. At 0.001 M conc. the coffee superiority was in the order of lactic, ascorbic, citric, phosphoric, malic, under-water soaking and no soaking. On averaging the quality points of


0.0001 M and 0.001 M concentrations, the quality of coffee was in the order of lactic, citric & ascorbic, phosphoric & malic, under-water soaking and no soaking. In general, the raw and roast characteristics were almost uniform for all the treatments except the control (No soaking). Under-water soaking of coffee

processed by dry fermentation enhanced the appearance of raw and roast quality of Ethiopian coffees consistently compared to coffee processed by dry fermentation only was established by Brownbridge and Sium (1971).

Table 1. Effects of natural fermentation + manual washing on coffee quality

Treatments 0.0001 M 0.001M

Raw Roast Liquor Total Order of

preference


preference

No soaking

(Control)

1.00 3.00 3.50 7.50 4 1.00 3.00 3.50 7.50 5

Under water

soaking

3.00 3.00 3.00 9.00 3 3.00 3.00 3.00 9.00 4

Citric 3.00 3.00 3.50 9.50 1 3.00 3.00 3.25 9.25 3

Malic 3.00 3.00 3.25 9.25 2 3.00 3.00 3.00 9.00 4

Lactic 3.00 3.00 3.50 9.50 1 3.00 3.00 3.75 9.75 1

Phosphoric 3.00 3.00 3.25 9.25 2 3.00 3.00 3.00 9.00 4

Ascorbic 3.00 3.00 3.25 9.25 2 3.00 3.00 3.50 9.50 2 All the values are average of three years results

Effects of enzyme treatment +machine washing on coffee quality subjected to acid soaking

Cup quality of coffee processed by enzyme treatment followed by machine wash and acid soaking are presented in Table 2. Parchment soaked under ascorbic acid recorded high quality points followed by soaking under phosphoric acid and water at the conc. of 0.0001 M, this was followed by citric & lactic, malic

and no soaking. At 0.001 M conc., the coffee quality improvement was in the order of ascorbic, under water soaking, citric, malic & lactic, phosphoric and no soaking. On averaging the points of both concentrations, the quality was found to be in the order of ascorbic, under water soaking, citric, lactic & malic, phosphoric and no soaking.

Table 2. Effects of enzyme treatment +machine washing on coffee quality

All the values are average of three years results



preference


preference

No soaking

(Control)

3.00 3.00 3.00 9.00 5 3.00 3.00 3.00 9.00 6

Under

water

soaking

3.00 3.00 4.00 10.00 2 3.00 3.00 4.00 10.00 2

Citric 3.00 3.00 3.50 9.50 3 3.00 3.00 4.00 10.00 3

Malic 3.00 2.00 4.25 9.25 4 3.00 3.00 4.00 10.00 4

Lactic 3.00 3.00 3.50 9.50 3 3.00 3.00 3.75 9.75 4

Phosphoric 3.00 3.00 4.00 10.00 2 3.00 2.00 4.00 9.00 5

Ascorbic 3.00 4.00 4.00 11.00 1 3.00 3.00 4.50 10.50 1


Effects of machine washing on coffee quality subjected to acid soaking

The outcome on coffee quality processed by machine wash followed by acid soaking are presented in the Table 3. In machine washed coffee, the best coffee quality was obtained from under-water soaking and soaking under citric acid, followed by phosphoric & malic acid. Ascorbic and lactic acids soaking were more

or less on par with control (no soaking) at 0.0001 M conc. At 0.001 M conc., the effect on cup quality was almost same for all the treatments as that of 0.0001 M conc. The main advantage of the soaking was to improve the raw and roast appearance by removing the browning of the coffees which is presumed to originate from degraded sugars and polyphenols as reported by Wootton (1971).

Table 3. Effects of machine washing on coffee quality

All the values are average of three years results

For better understanding the effect of acid

soaking on coffee quality, the total quality points awarded for the three demucilization methods (Natural fermentation, Enzyme treatment and machine wash) were averaged out and the final out come on effect of acids on coffee quality was found to be in the order of citric > under-water soaking > ascorbic > phosphoric > malic > lactic >un-soaked. The liquor characteristics of coffee processed by three different demucilization methods followed by acid soaking were specified in Table 4. From the table it was found that, coffee processed by natural fermentation followed by manual wash has good body, fair acidity but in flavour it has recorded slight bitter and medicinal taste. Interestingly, coffee demucilized by enzyme followed by machine wash and acid soaking recorded, fair to good body, fair to fair+ acidity and desirable sweetish flavour. Machine washed coffee showed fair to good body, Fair to good acidity and Slight bitter and harsh taste. Northmore (1965b) obtained improvement in coffee quality mainly by enhancement of its appearance in raw form, though this has little effect on liquor. However, Brownbridge (1966) observed a beneficial effect on liquor as well.

Slight improvement in quality due to under-water soaking and soaking in 1% sodium bi sulphite solutions for 24 hours was observed by Subramanian and Ashwat kumar (1968).

The result of soaking parchment coffee under acid solutions on coffee quality and the cost involved for soaking are presented in Table-5 and Figure-1. The added cost involved in use of acids for soaking wet parchment equivalent to a tonne of clean coffee at the conc. of 0.0001 M was found to be Rs.10/-, 10/-, 15/-, 20/- and 98/- for malic, phosphoric, lactic, citric and ascorbic acids respectively (Cost worked out based on 2007-08 price). In the present low price circumstances, the better acid for soaking naturally fermented coffee would be Phosphoric/malic better than citric or lactic though the later ones found to slightly in high order. In enzyme and machine washed coffee the better treatment for soaking parchment will be under-water soaking as there is no much difference between ascorbic acid and citric acid soaking in enzyme wash and machine wash respectively when compared to under water soaking.



preference


preference

No soaking

(Control)

3.00 3.00 3.00 9.00 5 3.00 3.00 3.00 9.00 6

Under

water

soaking

4.00 3.00 4.00 11.00 1 4.00 3.00 4.00 11.00 2

Citric 3.00 4.00 4.00 11.00 1 4.00 3.00 4.25 11.25 1

Malic 4.00 3.00 3.25 10.25 3 3.00 3.00 3.75 9.75 3

Lactic 3.00 3.00 3.00 9.00 5 3.00 3.00 3.75 9.75 5

Phosphoric 3.00 4.00 3.75 10.75 2 4.00 3.00 4.25 11.25 2

Ascorbic 3.00 3.00 3.25 9.25 4 4.00 3.00 3.50 10.50 4


Table 4. Effects of acid soaking on liquor quality of coffee processed by different

demucilization methods

Treatments Natural fermentation Enzyme treatment +

Machine wash

Machine wash alone

Acidity Body Flavour Acidity Body Flavour Acidity Body Flavour

No soaking (Control) Fair Good Bitter,

Harsh

Fair Good Sl.bitter Fair + Good Slight

Under-water soaking Fair Good Sl.bitter,

medicinal

Fair + Good Slight Fair + -

Good

Good Slight

Citric

0.001 M Fair Good Sl.bitter Fair + Fair -

Good

Slight Good Fair-

Good

Slight

0.0001 M Fair Good Sl.fruity Fair + Fair -

Good

Slight Fair + Fair-

Good

Slight

Malic

0.001 M Fair -

Fair+

Good Sl.bitter Fair -

Fair +

Good Slight Fair + Good Sl.bitter

0.0001 M Fair Good Tinge of

rawish

Fair + Fair -

Good

Sl.bitter Fair Good Very

bitter

Lactic

0.001 M Fair Good Sl.woody Fair + Good Slight Fair + Fair-

Good

Slight

0.0001 M Fair Good Sl.bitter,

medicinal

Fair -

Fair +

Good Sl.bitter,

harsh

Fair + Good Harsh,

bitter

Phosphoric

0.001 M Fair Good Sl.bitter,

medicinal

Fair + Good Slight Fair + Good Slight

0.0001 M Fair + Good Sl.fruity Fair + Good Sl.sweetish Fair + Fair-

Good

Slight

Ascorbic

0.001 M Fair + Good Sl.woody Fair + Good Sl.sweetish Fair + Good Harsh,

bitter

0.0001 M Fair Good Sl.woody,

bitter

Fair + Good Sl.sweetish,

bitter

Fair + Good Harsh,

bitter

Table 5. Comparison of acid soaking on coffee cup quality processed by different

demucilization methods

Treatments NF (A) Enzyme (B) Machine (C) Total Ave of

A+B+C

Order of

preference 1 2 1 2 1 2 1 2

No soaking (Control) 7.50 - 9.00 - 9.00 - 25.50 - 8.50 6

Under water soaking 9.00 - 10.00 - 11.00 - 30.00 - 10.00 2

Citric 9.50 9.25 9.50 10.00 11.00 11.25 30.00 30.50 10.08 1

Malic 9.25 9.00 9.25 10.00 10.25 9.75 28.75 28.75 9.58 4

Lactic 9.50 9.75 9.50 9.75 9.00 9.75 28.00 29.25 9.54 5

Phosphoric 9.25 9.00 10.00 9.00 10.75 11.25 30.00 29.25 9.87 3

Ascorbic 9.25 9.50 11.00 10.50 9.25 10.50 29.50 30.50 10.00 2 1 - 0.0001M concentration; 2 - 0.001 M concentration; NF- Natural fermentation


Fig 1. Effect of acid soaking coffee quality and cost involved

Conclusion

The present study indicates an improvement in appearance of raw bean as well as quality of liquor in all the treatments over control. ). The overall effect of acid soaking on coffee processed by 3 different demucilization methods were in the order of Citric > under-water soaking > Ascorbic > Phosphoric > Malic > Lactic > No soaking. In general coffee processed by natural fermentation+ manual wash + acid soaking had good body, fair acidity and slight bitter/medicinal taste. Coffee processed by enzyme + machine wash+ acid soaking recorded fair to good body, fair to fair plus acidity and sweetish flavour. Coffee processed by machine wash alone recorded, fair to good body, fair to good acidity and slight bitter/harsh taste.More comprehensive studies are essential to determine the optimum concentrations of acids to be used, period of soaking, solid losses and effect of soaked water on pollution load.

References

Brownbridge, J.M. (1966). The use of sodium meta bisulphite in the processing of Tanzanian coffees. Proc. Of the First Specialist meeting on Coffee Research in

East Africa, Nairobi (Kenya), East African Agriculture and Forestry Research Organisation. pp.344-348.

Brownbridge, J.M. and Sium, M. (1971). Coffee processing research in Ehiopia. Fermentation and its effect on liquor quality, Kenya Coffee., Vol. 207, pp.214. Mburu, J.K. (1999). Notes on coffee processing procedures and their influence on quality, Kenya Coffee., Vol. 75, pp.2861-2867. Northmore, J.M. (1965a). The use of sodium bisulphite in coffee fermentation, Kenya Coffee., Vol.30, pp.285-286. Northmore, J.M. (1965b). Sodium bisulphite in coffee fermentation, Kenya Coffee., Vol.31, pp.217-221. Terry Mabbett. (1999). Origin detectives, Coffee and Cocoa International., Jan/Feb. pp.37. Subramanian, T.R and Ashwat kumar, B.S. (1968). Preliminary studies on the effect of under water and sodium bisulphite soaking on the quality of coffee, Indian Coffee., Vol. XXXII, pp. 1-3.

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Viani, R. (2000). Global perspectives in coffee quality improvement, Proceedings of International Scientific Symposium on Coffee, Bangalore,India. Wootton, A.E. (1963). The fermentation of coffee, Kenya Coffee.,. Vol.28, pp.317.

Wootton, A.E. (1971). Report C.R. 14, Nairobi, May. The influence of wet processing of Arabica coffee upon the characteristics of the coffee bean.

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