Fermented foods
Practical Action
example, one design has a slowly rotating basket that is fitted with internal baffles to mix
the substrate. The slow rotation equalises the temperature and aerates the food with air to
provide oxygen for cell growth and to control moisture loss by evaporation.
Fermented cereals, legumes and root crops
Leavened breads are produced by first mixing the yeast, Saccharomyces cerevisiae, with flour,
water and other ingredients to form a dough (see Technical Brief: Baking). This is then
fermented in a proving cabinet to produce carbon dioxide, which leavens the dough. Ethanol is
also produced in small amounts but it is evaporated when the dough is baked. In sour dough
fermentations, lactic acid bacteria and yeasts are used to ferment different cereal/legume
mixtures using similar equipment. The proving cabinet has a controlled temperature of 35-
43oC and humidity of ≈ 85%. Commercial proving cabinets are made from stainless steel, with
humidifiers and thermostatically controlled electric heaters to control the temperature and
humidity. A simple low-cost prover can be made using a wooden or metal framework covered in
polythene sheeting with a flap to gain entry (Fig. 1). Dough is placed on shelves inside the
prover and the raised temperature and humidity are created by gently boiling a pan of water in
the cabinet. A larger prover can be made from a steel container of the type that is used to
carry goods aboard ships and on trucks. It is converted to a prover by fitting it with an
insulated pipe to supply steam from an external boiler. This raises the temperature and
humidity. The dough is loaded into the prover on wheeled trolleys and the container doors are
closed while proving takes place.
Batters made using a variety of cereal and legume floursare
fermented by lactic acid bacteria without control of the
temperature or humidity and heated on a griddle to produce
leavened pancakes, including idli from lentils and rice in India,
and injera from tef in Ethiopia (Table 1). In all products, the
baking stage destroys the fermentation micro-organisms.
Fermented porridges are made from milled maize, millet,
sorghum, cassava and yam. Examples include gari, a creamy-
white, granular flour, made in West Africa from fermented
cassava. The tubers are washed, peeled and grated and the
grated cassava is fermented by a mixture of naturally occurring
bacteria by packing it into baskets and leaving it at ambient
temperature for 5 days. The fermentation both removes toxic
cyanide compounds and produces the desirable flavours. After
fermentation, the cassava is pressed to remove water and then
roasted using a hot pan. Roasting destroys enzymes and micro-
organisms; drives off the cyanide gas; causes partial
gelatinisation of the starch; and dries the product. Fufu is
another West African fermented cassava product that is produced
by soaking peeled whole or sliced cassava roots in vats for 3-4
days. During soaking, a natural fermentation increases the acidity,
softens the tubers, and reduces the concentration of cyanide
Figure 1: Low-cost dough
prover. Photo: Pete
Fellows.
compounds. After fermentation, the softened tubers are grated to
a paste and sieved to remove larger fibres. This is mixed with water, allowed to settle for 24
hours and the water is then poured off and the sediment pressed to dewater it. The resulting
cake is sieved and dried. When properly packaged and stored, dried fufu and gari flours have a
shelf life of six months or more.
In Ghana, kenkey is prepared from maize flour mixed with warm water to make a dough. A
natural fermentation takes place for 2-3 days at ambient temperatures, and the fermented
dough is then kneaded until it is slightly stiffened. It is divided into two equal parts: one part
(named ‘aflata’) is partially boiled in water for ≈10 minutes, stirring constantly and vigorously.
This is then mixed with the remaining uncooked dough and the aflata-dough mixture is divided
into portions and wrapped tightly in banana leaves, cornhusks, or foil. These are steamed for
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