CHAPTER 7
PRODUCTS OF MIXED FERMENTATIONS
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Most traditional fermented food products are made by a complex interaction of different micro-organisms. This chapter deals with the products made when there is not a single dominant set of micro-organisms.
Vinegar is the product of a mixed fermentation of yeast followed byacetic acid bacteria. Vinegar, literally translated as sour wine, is one of the oldestproducts of fermentation used by man. It is the acetic acid produced by the fermentationof alcohol (ethanol) which gives the characteristic flavour and aroma to vinegar.
It can be made from almost any fermentable carbohydrate source, forexample fruits, vegetables, syrups and wine. The basic requirement for vinegar productionis a raw material that will undergo an alcoholic fermentation. Apples, pears, grapes,honey, syrups, cereals, hydrolysed starches, beer and wine are all ideal substrates forthe production of vinegar. To produce a high quality product it is essential that the rawmaterial is mature, clean and in good condition.
Indigenous vinegars can be made quite simply by the spontaneousfermentation of a fruit or alcohol. All that is necessary is an alcoholic substrate,strains of acetic-acid forming bacteria (acetobacter) and oxygen to enable theoxidation of alcohol. However, this process is very slow and vinegars produced by thismethod tend to be of inferior quality. Controlled fermentation conditions produce a moreacceptable product. A wide range of raw materials can be made into vinegar.
Location of production
Throughout Asia particularly the Philippines and Sri Lanka
Product description
A clear liquid with a distinctive acetic acid taste with a hint of acoconut flavour.
Raw material preparation
Coconut water is a waste product, which is produced in appreciablequantities in the Philippines, Sri Lanka Thailand and other countries. Its conversion intovinegar therefore presents an attractive option for decreasing wastage and producing avaluable product.
Processing
Coconut water is a good base for vinegar, but its sugar content is toolow (only about 1%). Sugar needs to be added to bring the level of sugar up to 15%. Afterthe addition of sugar, the coconut juice is allowed to ferment for about seven days,during which time the sugar is converted to alcohol. An alternative method is topasteurise the coconut water and sugar mixture and add yeast.
After this initial fermentation, strong vinegar (10% v/v) is added tostimulate the growth of acetic acid bacteria and discourage further yeast fermentation.The acetic acid fermentation takes approximately one month, yielding a vinegar withapproximately 6% acetic acid. The fermentation will take less time than this if agenerator is used.
After fermentation, the vinegar must be stored in anaerobic conditionsto prevent spoilage by the oxidation of acetic acid. (Steinkraus, 1996)
Clarification can be achieved by stirring with a well beaten egg white,heating until the egg white coagulates and filtering (Anon).
Location of production
Latin America and Asia
Product description
This product enables the utilisation of pineapple peels, which areusually discarded during the processing or consumption of the fruit. The product has adistinct, very light pineapple flavour and has the same uses as any commercial vinegar.
Raw material preparation
The peels should be from very well washed ripe pineapples (damaged,rotten or infected fruits should not be used as a source of peels). Use only the peels,not the leaves or stems. The water used should be potable water, boiled if necessary. Allthe equipment should be well cleaned, as well as the bottles, which should also besteam-sterilised before use.
Processing
The peels should be cut into thin strips and put into clay or pewterpots. Aluminium or iron pots should not be used.
Sugar and clean water are added. Each pot is then inoculated andcovered with a clean cotton cloth, held around the pot with an adhesive tape, to preventcontamination by insects or dust. The inoculated pineapple is fermented at roomtemperature (about 20-220C) for about eight days. The acidity should be checkeddaily. The water level should be maintained during this period. The product should beincreasingly acid and by the eighth day it should have the required concentration of 4 percent acetic acid in vinegar. If higher acidity is desired the product is left to fermentfor another one or two days.
The development of acidity should be checked by tasting the productduring fermentation.
The residual bacteria removed may be reused as a residue inoculum twoor three times more.
The traditional process may be improved by a two-stage fermentation inwhich alcohol is first formed by yeast (Saccharomyces cerevisiae) and themust is then inoculated with acetic acid bacteria (Acetobacter pasteurianus).In outline, the process involves liquidising the peels and diluting with water (water:pulpis 4:1), adjusting the pH to 4.0 using sodium bicarbonate and adding yeast nutrient(ammonium phosphate) at 0.14g per litre. A starter culture is added at 2.7g per litre andthe fermentation allowed to take place at 250C for two days. Themust is then filtered and inoculated with acetic acid bacteria and allowed toferment for eleven days with aeration of the must. Other parts of the processare similar. Additional equipment includes a pH meter, refractometer, liquidiser,fermentation locks and equipment for preparing the starter cultures (Fellows, 1997).
Flow Diagram
| Pineapple | Well washed in clean water |
| Peel the fruit | Take care not to damage hands |
| Cut the peel | Cut into thin strips and put into clay or pewter pots |
| Mix with sugar | Sugar is dissolved in clean water |
| Ferment | Each pot is then inoculated and covered with a clean cotton cloth |
| Filter | Strain through a cheese cloth |
| Package |
Packaging and storage
The vinegar is bottled in clean glass bottles and stored in a cool darkplace.
Palm wine vinegar is a produced across West Africa. It is a vinegarcontaining about 4% acetic acid, produced from the oxidation of palm wine. It is mainlyconsumed by people in urban areas as a salad dressing and meat tenderiser, although italso has medicinal uses and is valued in certain rituals. Palm wine is fermented using thesame process as for grape wine vinegar the oxidation of alcohol to acetic acid. Thespontaneous process takes about four days. The optimum fermentation temperature is 30º C.
Coconut toddy vinegar is produced throughout South Asia particularlySri Lanka. It is a clear liquid with a strong acetic acid flavour and a hint of coconutflavour. The fresh toddy is strained, prior to allowing yeast fermentation to occurnaturally for 48 to 72 hours. The yeast cells and debris are then removed by progressivesedimentation. After two to four weeks of settling the fermented toddy is placed inbarrels. The alcohol is then converted into acetic acid by acetic acid bacteria which arenaturally present. The process can be hastened by adding vinegar as a starter. Thefermented toddy is converted into vinegar in about three months. Ageing for six months,results in a pleasantly flavoured final product (Jayawardena, 1977).
In East Asia particularly Papua New Guinea a vinegar is made from thesap of the Nipa palm (Nypa fruticans) (Paivoke, Adams and Twiddy, 1984).
Quick process pickles are easy to make but do not really constitute afermented food product. For this technique, vegetables are soaked in a low salt solutionfor a few hours. They are then drained and placed in a container. The container is filledwith a hot vinegar and spice mixture or a hot oil and spice mixture (Kordylas, 1990).There are hundreds of different recipes utilising locally available fruit and vegetables.For instance the book "Pickles of Bangladesh" has recipes for mango sour pickle,sliced mango pickle, sweet olive pickle, hot olive pickle, sweet tamarind pickle, chaltapickle and green chilli pickle (Azami, 1994).
Location of production
Africa, Asia and Latin America particularly Cote d'Ivoire, Ghana,Indonesia and Brazil.
Product description
A fine brown powder with the characteristic taste of cocoa. It is amajor ingredient in the confectionery and bakery industries. The product has a short shelflife. "Drinking chocolate" is a mixture of cocoa powder and sugar.
Raw material preparation
Cocoa beans are the seeds of the cocoa plant (Theobroma cacao).Cocoa pods are cut from the cocoa tree. The pods are cut and the beans removed. Only fullyripe and undamaged beans should be selected. It is important that the beans are processedquickly.
Processing
It was formerly believed that cocoa beans were fermented to remove theadhering pulp (Wood, 1990). However a good flavour in the final cocoa or chocolate isdependent on good fermentation. Fermentation is carried out in a variety of ways but alldepend on heaping a quantity of fresh beans with their pulp and allowing micro-organismsto produce heat (Beckett, 1988). The majority of beans are fermented in heaps althoughbetter results are obtained using boxes, which result in a more even fermentation.
Fermentation lasts from five to six days. During the first day theadhering pulp is liquified and drains away with the temperature rising steadily. Theinitial alcoholic fermentation gives way to acetification. This and other chemical changescause the temperature to rise in excess of 50oC. The beans die. It was thoughtin the past that death was mainly due to increasing temperature. It is now known thatacetic acid at a concentration of 1 percent in the bean is the cause of death and that itis only enhanced by heat, lactic acid and ethanol. The pH value of the cotyledon dropsfrom 6.45 to 4.5 over 120 hours and that during the same period the acetic acid contentincreased from 0 to 1.36 percent, while the lactic acid content increased from 0.005 to0.12 percent. When the bean dies maceration of the tissue takes place, allowing enzymesand substrate to mix freely. The possible substrates for enzymes are carbohydrates,lipids, phenolics and amino acids. In addition it is known that the bacteria canmetabolise alcohols and organic acids of various kinds. The changing chemical picture iscomplex. Possible major substrates for micro-organisms are carbohydrates, lipids,phenolics and amino acids. Unlike some flavours and aromas, that of chocolate is notattributable to a single compound (Carr, 1985) (Minifie, 1980).
During fermentation the external appearance of the beans changes. Atfirst they are pinkish with a covering of white mucilage. Gradually the colour darkens andthe mucilage disappears. The beans on the surface are always darker than those deeper inthe heap or box, indicating that the colour change is oxidative. As the beans are mixed,their colour becomes a more uniform orange-brown and they are only slightly sticky. Atthis stage they are ready for drying.
The beans need to be dried to a moisture content of less than 7.5%. Thebeans are dried by either being spread out in the sun in layers a few centimetres thick orin artificial dryers. There are numerous types of dryers but it is important that anysmoky products of combustion do not come in contact with the beans otherwise taints willappear in the final product.
The beans are cleaned to remove the extraneous matter.
Cocoa beans consist of an outer skin that needs to be removed and inner"nib". The shell is sometimes removed before roasting and sometimes afterroasting.
For cocoa powder roasting temperatures of 120 to 150°C are used. There are many designs of roasters: both batch and continuous systems. Theoperation is controlled so that the cocoa is heated to the required temperature withoutburning the shell or the cotyledon. The heat is applied evenly over a long period of up to90 minutes to produce even roasting. The bean must not be contaminated with any combustionproducts from the fuel used and provision must be made for the escape of any volatileacids, water vapour and decomposition products of the bean (Wood, 1980) (Cakebread, 1975).After roasting the beans are cooled quickly to prevent scorching.
The roasted nibs are ground into a powder in a plate mill. Theresulting powder is sieved through fine silk, nylon or wire mesh.
To produce cocoa powder, some of the cocoa butter needs to be removed.With low fat cocoa powder, more than 90% of the cocoa butter is removed. With medium fatcocoa powder, more than 78% of the cocoa butter has been removed. Finally high fat cocoapowder has less than 78% of the cocoa butter removed. Extrusion, expeller, or screwpresses are used in the cocoa industry to remove the cocoa
The cake from the mill is ground in a hammer mill to produce the cocoapowder.
Flow diagram
| Cocoa beans | |
| Sort | Select only mature beans |
| Ferment | In heaps or boxes |
| Clean | Remove extraneous material |
| Dry | In the sun or in artificial dryers |
| Roast | 120 to 150° C |
| Grind | |
| Remove cocoa butter | |
| Grind cake | |
| Pack |
Packaging and storage
Cocoa powder is hygroscopic (picks up moisture from the air) and should be protected, especially in humid climates. Lidded tins or sealed polythene bags should be used.
Location of production
Throughout Africa, Asia and Latin America.
Product description
A brown solid oily product with the characteristic taste of chocolate.It is a major ingredient in the confectionery and bakery industries.
Preparation of raw materials
Cocoa beans are the seeds of the cocoa plant (Theobroma cacao).Cocoa pods are cut from the trees, and the beans are removed from the pods. Only fullyripe and undamaged beans should be selected. It is important that the beans are processedquickly.
Processing
Fermentation, drying and cleaning of the beans have been described in Section 7.2.1.
For cocoa butter production the roasting temperatures are 100° C to 104° C There are many designs of roasters: both batch and continuous systems. The operation is controlled so that: the cocoa is heated to the required temperature without burning the shell or the cotyledon The heat is applied evenly over a long period of up to 90 minutes to produce even roasting; the nib must not be contaminated with any combustion products from the fuel used and provision must be made for the escape of any volatile acids, water vapour and decomposition products of the nib (Wood, 1980) After roasting the beans are cooled quickly to prevent scorching
Roasting will have already loosened the shell. The beans are thenlightly crushed with the object of preserving large pieces of shell and nib and avoidingthe creation of small particles and dust. The cocoa bean without its shell is known as a"cocoa nib". The valuable part of the cocoa bean is the nib, the outer shellbeing a waste material of little value.
Alkalization is a treatment that is sometimes used before and sometimesafter grinding to modify the colour and flavour of the product. This was developed in theNetherlands in the last century and is sometimes known as "Dutching". Thisinvolves soaking the nib or the cocoa mass in potassium or sodium carbonate. By varyingthe ratio of alkali to nib, a wide range of colours of cocoa powder can be produced(Glossop, 1993). Complete nib penetration may take an hour. After alkalizationthe cocoa needs to be dried slowly.
The cocoa nib is ground into "cocoa liquor" (also known as"unsweetened chocolate" or "cocoa mass"). The grinding processgenerates heat and the dry granular consistency of the nib is turned into a liquid as thehigh amount of fat contained in the nib melts (Gates, 1990)..
There are various pre-treatments to develop the flavour of the cocoamass with and without reaction solutions. These include the "Luwa thin-layerevaporator", "Petzomat thin-layer process", "Cocovap process","Lehman KFA process" and "Carle-Montanari process" (Beckett, 1988).
Extrusion, expeller, or screw presses are used in the cocoa industryfor the production of cocoa butter from whole beans, and mixtures of fine nib dusts, smallnibs, and immature beans. Research in the Kerala Agricultural University has led todevelop a suitable pressure device capable of separating cocoa butter from ground cocoamass ideally suitable for small scale manufacturers (Ganeshan, 1990). In Peru asimple screw press is used to extract cocoa butter from beans. The crude cocoa butter isfiltered through cloth and allowed to solidify.
To produce plain chocolate, cocoa mass is mixed with sugar andsufficient cocoa butter to enable the chocolate to be moulded. The ratio of mass to sugarvaries according to the national taste. The mixture is ground to such a degree that thechocolate is smooth to the palate. At one time this was done by a lengthy process inmelengeurs - heavy granite rollers in a revolving granite bed - but nowadays grinding isdone in a series of rolls.
The chocolate is then "Conched". This may last for severalhours. The chocolate is heated, this helps to drive off volatile acids, thereby reducingacidity when present in the raw bean, and the process finishes the development of flavourand makes the chocolate homogeneous (Wood, 1980) ). Similar processes are involved in themanufacture of milk chocolate. The milk is added in various ways either in powder form tothe mixture of mass, sugar and cocoa butter, or by condensing first with sugar, adding themass and drying this mixture under vacuum. The product is called crumb andthis is ground and conched in a similar manner to plain chocolate. After conching thechocolate has to be tempered before it is used for moulding or for enrobing confectionerycentres. Tempering involves cooling and reaching the right physical state for rapidsetting after moulding or enrobing.
Location of production
Throughout Africa, Asia and Latin America particularly Brazil,Colombia, Indonesia, Mexico and Cote d'Ivoire.
Product description
A fine dark brown powder made from roasted coffee beans. Brewed withboiling water and consumed as a drink.
Raw material preparation
Coffee beans are harvested from two plants Coffea arabica andCoffea canephora variety robusta. Only ripe berries should be used in coffeeproduction. Berries can be placed in water so that immature berries which float can beidentified and discarded.
Processing
Dry processing is the simpler of the two processing methods and ispopular in Brazil for the processing of Robusta coffee and in Sri Lanka forprocessing Arabica coffee. The coffee cherries are dried immediately after harvestby sun drying on a clean dry floor or on mats. The dried berry is then hulled to removethe pericarp. This can be done by hand using a pestle and mortar or in a mechanicalhuller. The mechanical hullers usually consist of a steel screw, the pitch of whichincreases as it approaches the outlet so removing the pericarp. The hulled coffee iscleaned by winnowing.
Wet processing involves squeezing the berry in a pulping machine orpounding in a pestle and mortar to remove the outer fleshy material (mesocarp and exocarp)and leave the bean covered in mucilage. This mucilage is removed by fermentation.Fermentation involves placing the beans in plastic buckets or tanks and allowing them tosit, until the mucilage is broken down. Natural enzymes in the mucilage and yeasts andbacteria in the environment work together to break down the mucilage. The coffee should bestirred occasionally and every so often a handful of beans should be tested by washing inwater. If the mucilage can be washed off and the beans feel gritty rather than slippery,the beans are ready.
There is much debate about the fermentation of coffee beans. Someresearchers feel that the mucilage breakdown is caused by enzymatic breakdown. Forinstance Wellman has stated that enymatic fermentation starts immediately the beans havebeen squeezed from the fresh berries. If these pulped beans are piled up orput in a container and protected from any bacterial or other contamination thefermentation will progress. After a number of hours the enzymes of the pulp will haveacted on the torn tissues, gorged with starches, sugars and pectins, in such a mannerthat, without any microbial intervention, the remaining pulp will be easily detached fromthe beans and washed off in water (Wellman, 1961). However most investigators acknowledgethe necessity for the presence of micro-organisms for the depectinisation of the beans.
The following micro-organisms have been isolated: Leuconostocmesenteroides; Lactobacillus plantarum; Lactobacillus brevis, Streptococcusfaecalis, Aerobacter (Enterobacter) and Escherichia, pectinolyticspecies of Bacillus, Saccharomyces marscianus, S. bayanus and a Flavobacteriumsp., Erwinia dissolvens, Fusarium spp, Aspergillus spp and Penicillium.(Pedersen and Breed) (Vaughn et al., 1958) (Hilmer et al.,1965), (Agateand Bhat, 1966)
The beans should then be washed immediately as 'off' flavours developquickly. To prevent cracking the coffee beans should be dried slowly to 10% moisturecontent (wet basis). Drying should take place immediately after to prevent 'off' flavoursdeveloping. The same drying methods can be used for this as for the dry processed coffee.After drying the coffee should be rested for 8 hours in a well ventilated place. Thethin parchment around the coffee is removed either by hand, in a pestle and mortar or in asmall huller. The hulled coffee is cleaned by winnowing.
The final flavour of the coffee is heavily dependent on how the beansare roasted. Roasting is a time temperature dependent process. The roasting temperatureneeds to be about 200° C. The degree of roast is usuallyassessed visually. One method is to watch the thin white line between the two sides of thebean, when this starts to go brown the coffee is ready. As preferences vary considerablyfrom region to region, a lot of research will need to be done to find the locallyacceptable degree of roast. Coffee beans can be roasted in a saucepan as long as they arecontinually stirred. A small improvement is made by roasting the coffee in sand, as thisprovides a more even heat. A roaster will produce a higher quality product.
Grinding is a means of adding value to a product. However, it isfraught with difficulties. It is easy to make an assessment of an intact bean, while aground product presents some difficulty. The fear of adulteration and the use of lowquality produce is justified. Because of this there is a great deal of market resistanceto ground coffee. This market resistance can only be overcome by consistently producing agood product. There are basically two types of grinders - manual grinders and motorisedgrinders (anon, 1995).
Flow diagram
| Coffee cherry | |
| Sort the cherries | Select only mature undamaged beans |
| Pulp | Skin and pulp removed |
| Ferment | To remove mucilage |
| Dry the beans | Sun drying or artificial drying |
| Roast | |
| Grind | |
| Package |
Packaging and storage
Roasted beans can be stored in sacks. Milled beans need to be packaged quickly to prevent the loss of volatile flavour components. The packaging material should be airtight. Polythene is not suitable as it is a low barrier to loss of aroma (Fellows, 1997).
7.4 Other mixed fermentation products
Vanilla is produced in Madagascar, Indonesia and various South Pacific islands. Itis a dark brown pod about 20 cm in length. Vanilla is produced by fermenting the pods ofthe orchids of the genus vanilla. The pods are first sun dried for 24 to 36 hours and thenblanched in hot water (65° C) for two to three minutes. Thepods are then fermented in boxes and dried again.
Tabasco sauce is made in Mexico and Guatemala. The chilli pods areharvested, ground into a paste and placed in a container with salt. The hot and fierysauce develops.
In the production of tea, there is a process referred to as fermentation. However microbial activity is not involved in the so-called fermentation of tea. The chemical changes are effected by enzymes alone. Fermentation rooms are used where moisture and temperature can be controlled. During fermentation even further darkening of the leaf occurs and the typical aroma develops. By subjective judgement of the aromas intensity the period necessary for completion is gauged (Carr, 1985).
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