Fermented foods
Practical Action
the fermentation vessel. The flavour of the lager depends on the ingredients, the strain of
yeast and the fermentation temperature.
Other types of beer include maize beer (Chicha de jora) in Latin America and sorghum beer in
Eastern and Southern Africa. This is brownish-pink with a fruity, sour taste and an alcohol
content of 1-8%. It is not filtered and appears cloudy, and it may also contain small pieces of
grain. It is produced using malted sorghum mash, which is first soured by lactic acid bacteria
and then fermented by yeasts in a similar way to other beer fermentations. The lactic acid
bacteria may be added from yoghurt or a sour dough, or the bacterial that occur naturally on
the sorghum grain may be used. Commercial sorghum beer is packaged with the fermentation
still active and for this reason, special containers with vents are used to allow the gas to
escape.
After fermentation, most beers are allowed to clear, with the yeast and other materials settling
out as sediment in the fermentation tank. At larger scales of production, the beer is filtered
and/or centrifuged, often using filter aids to produce crystal-clear products. Beers may be
filtered and bottled directly if they are to be consumed within a few days. For a longer shelf
life, they may be pasteurised after filling into bottles, or at a larger scale they are pasteurised
before filling into bottles, cans or kegs. The alcohol content of beers and lagers is typically 2-
6%, measured using a hydrometer. If a standard alcohol content is required, beers from
different batches are blended, based on the hydrometer readings.
Wines may be produced from almost any plant material that contains sufficient amounts of
sugar, including most fruits and some types of tree sap (e.g. maple sap, or palm sap used to
make palm wine or ‘toddy’ - see Technical Brief Toddy and Palm Wine). Some types of
vegetables or young vegetable pods (e.g. pea pods) can also be fermented with added sugar.
Worldwide, grapes are the preferred fruits to make high quality wines (see Technical Brief:
Grape wine). The most popular non-grape wines in many countries are pineapple, papaya,
passion fruit, banana, melon and strawberry. ‘Fortified’ wines, such as sherry, port, ginger
wine etc., have alcohol contents of 15-20%.
The important factors for the production of good quality wines are: 1) a suitable wine yeast
that is added in sufficient amounts (e.g. 1-2%) to rapidly start a vigorous fermentation; 2)
strict attention to cleanliness and hygiene, with sterilisation of fermentation vessels and all
other equipment using sodium metabisulphite solution; 3) exclusion of air with an airlock to
prevent micro-organisms converting the alcohol to vinegar; 4) a fermentation temperature of
ideally 20-25oC, but ambient temperature usually is satisfactory if it is not below ≈ 18oC; 5)
sedimentation and filtration after the fermentation has finished to produce a crystal-clear
wine.
Glass ‘demijohns’ (Figure 2a) are popular fermentation vessels for micro-scale production of
wines because they are transparent to check that they are clean and to monitor the
fermentation, but any container made from food-grade material is suitable. All fermentation
vessels should be fitted with an airlock (Figure 2b) to prevent contamination by micro-
organisms from the air and to ensure that carbon dioxide from the fermentation replaces the
air above the fermenting liquor and so reduces the risk of oxidation of wine to vinegar.
7