Fermented foods
Practical Action
1-3 hours, depending on the size of the portions and the final product is consumed on the
same day that it is produced.
Different types of light and dark soy sauce, tamari and similar products are made by a two-
stage fermentation: in the first stage a mixture of cooked soybeans and roasted wheat flour is
fermented by the moulds Aspergillus oryzae and A. soyae for 3 days at 30°C. The fungal
enzymes break down starch and proteins, and these form the substrate for the second
fermentation. The fermenting mixture (named ‘koji’) is transferred to 18-20% brine in deep
tanks and lactic acid bacteria are inoculated. The fermenting mixture is kept at 15oC for the
first month, allowing the pH to fall from 6.5 to 5.0. Then cultures of the yeasts
Zygosaccharomyces sp. and Candida sp. are added and the temperature is increased slowly to
25-28°C to allow an alcoholic fermentation to take place for 3-6 months. During this time the
sauce develops its characteristic flavour. The liquid is collected, filtered, pasteurised and
bottled. The final product has a pH of 3.3-5.3 and is preserved by the salt and a low
concentration (≈2.5%) of ethanol.
Tempeh is another fermented soybean product, made by soaking beans at 25°C, removing the
seed coats and steaming the split beans for 0.5-2 hours. These are inoculated with spores of
the fungus, Rhizopus sp., packed into trays or rolled in banana leaves, and incubated at 32°C
for 20 hours. The fungus softens the beans and binds the bean mass to form a solid cake. The
fermentation changes the texture and flavour of the soybeans but has little preservative effect.
The product is sliced, dipped in salt water and fried within a few days, or preserved for longer
periods by chilling or freezing. In Japan, sake is an alcoholic beverage with an alcohol content
of 13-17%, produced by first growing Aspergillus oryzae on steamed rice mash to produce
koji. This is then mixed with more rice mash and the starch is converted to sugars by enzymes
in the koji. A mixture of yeasts produce an alcoholic fermentation and the liquor is separated
from the fermented mash after 10-13 days and distilled. Other fermented cereal and legume
products include dhokla (chickpeas), brem (rice), miso (rice and soybeans), dosa (rice) and idli
(rice and black gram) in Table 1.
Fermentation is also used in the processing of coffee and cocoa beans: after removal of the
outer skin, coffee berries are soaked in water and allowed to ferment. Bacteria first break down
the berry pulp, followed by a lactic acid fermentation that increases the acidity and develops
flavour compounds that contribute to the final coffee flavour after the beans have been dried
and roasted. Similarly, in cocoa fermentation, yeasts and lactic acid bacteria break down the
pulp around the beans and contribute to the aroma, flavour and colour of the cocoa.
Fermented vegetables
Important fermented vegetables include sauerkraut from cabbage, kimchi from cabbage,
radish and green onion, atchara from mixed fruits and vegetables, gundruk from leafy
vegetables, and zha cai from mustard plant stems (Table 1). These are produced by dry
salting, in which alternate layers of chopped or shredded vegetables and salt are packed into
sealed jars, barrels or tanks. Juice is extracted from the vegetables by the salt to form a sweet
brine, which is then fermented by lactic acid bacteria. The natural fermentation involves a
succession of different lactic acid bacteria, each more tolerant of the increasing acidity.
Further details are given in the technical briefs listed in the introduction.
Fermented meat and fish products
Fermented sausages are described in Technical Brief: Fresh and Cured Sausages. There are a
large number of fish or seafood sauces made from fermented whole raw fish, dried fish or
shellfish, or from the blood or viscera of different species (e.g. shiokara and bagoong in Table
1). Some sauces contain only fish and salt, whereas others are flavoured with a variety of
herbs and spices. A short fermentation results in a pronounced fishy taste, whereas longer
fermentation times produce nuttier and cheesier flavours. These sauces are popular in
Southeast Asian countries, where they are used as cooking ingredients, condiments,
flavourings or dipping sauces. For example, sauce made from anchovies is produced by
layering the fish and salt in wooden boxes. The fish are slowly pressed as they ferment, to
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