Fermented foods
Practical Action
produce the liquid sauce. Semi-solid fish pastes (prahok in Cambodia, trasi in Indonesia and
belacan in Malaysia) are other variations of the sauce. Also in Malaysia, fresh small prawns or
krill are mixed with salt and rice and sealed in jars to ferment for three days and produce the
condiment cincalok. In Europe, Worcester sauce is made from a fermented mixture of
molasses, sugar, salt, anchovies, vinegar, tamarind extract, onions, garlic, spices, and other
flavourings. The ingredients are sealed in barrels and allowed to ferment for several weeks and
the liquor is drawn off to make the sauce.
Liquid (or submerged) fermentations
At a small scale, the most important fermentations using liquid substrates are:
• Alcohol production, including wines made from fruits, honey, tree saps, rice and vegetable
pods. Beers are produced from malted (partly germinated) barley and other cereals,
including wheat in temperate climates, and maize, sorghum and millet in tropical
countries.
• Dairy fermentations, including lactic acid fermentations of milk to make acidified milks,
yoghurts and cheeses.
• Pickled vegetables and
• Vinegar production, which is a two-stage process that involves an alcohol fermentation
followed by a fermentation using acetic acid bacteria that convert the alcohol to vinegar
(acetic acid).
For small-scale production, the equipment for fermentation of beers, pickles and fermented
dairy products usually consists of a covered container, such as plastic, aluminium or stainless
steel buckets, drums or tanks. Note: some producers use jerrycans that are intended to carry
fuel or water, but this should be discouraged because they are more difficult to inspect to
ensure that they are properly cleaned, and some types are made from plastics that are not
food-grade. Likewise, re-used steel oil drums should be avoided due to the risk of
contamination, or corrosion of the steel by acidic products. Stainless steel batch fermenters
are commercially available in sizes that are suitable for small-scale operation, but they are
relatively expensive, mostly because of the systems that are used to control the fermentation
process (i.e. the temperature, acidity, dissolved oxygen, degree of agitation and foaming).
In outline, liquid fermentations involve preparing the liquid substrate, pasteurisation,
inoculation with the required micro-organism(s), fermentation, followed for some products by
sedimentation or filtration and separation of the fermented product. The following section
gives an outline of fermentation processes used to make beers and wines. Processes for
vinegar, dairy products and pickled vegetables are described in Technical Briefs listed in the
introduction.
Beers and wines
Note: In some countries a special licence is needed to produce and sell any alcoholic
products, whereas in others it is only distilled spirits that need a licence. Alcohol production is
not permitted in some Muslim countries. Producers should ensure that they have the correct
licences or permits to avoid the risk of prosecution.
Beer ‘wort’ is produced by boiling malted cereal grains to release sugars, which are then
fermented by the yeast, Saccharomyces cerevisiae. Some have added hops to produce
bitterness in the beer. Variations in the composition of the wort, the strains of yeast and the
fermentation time and temperature, each result in the hundreds of different types of beers
that are produced. ‘Top-fermenting’ yeast strains are used at temperatures from 12-25°C and
rise to the surface during fermentation, creating a thick ‘head’. They produce high levels of
flavour compounds that give the distinctive character to beers, ales, porters and stouts. For
example, wheat beers have a lighter colour and more delicate flavour than beers made with
barley and other grains, and many wheat beers are cloudy. Lager yeast (S. carlesbergensis) is a
bottom-fermenting yeast that is used at temperatures from 7-15°C. This yeast grows less
rapidly than top-fermenting yeast; produces less surface foam, and settles out to the bottom of
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