Soy sauce

The history of soy sauce in Japan can be traced back some 3000 years: it probably arrived in Japan from China with the introduction of Buddhism. Although there is an acid-based chemical method for making the product, we focus only at the fermentative route to soy sauce.

Five types of soy sauces are recognised by the Japanese government (Table 14.2). The major types of soy sauce are Koikuchi, which accounts for some 90% of the total market and is a multi-purpose seasoning with a strong aroma and a dark red/brown colour, and Usukauchi, which is lighter and milder and is employed in cooking when the original food flavour and colour are paramount.

All soy sauces comprise 17-19% salt, seasoning and flavour enhancers.

The overall procedure involved in making soy sauce is given in Fig. 14.1. There are basically two different processes, namely the soaking and cooking of soybeans and the roasting and cracking of wheat.

The soybeans may be whole or the starting material may be de-fatted soybean meal or flakes. When whole beans are used, the oil must ultimately be removed to avoid the production of an unsatisfactory product.

The use of pressed or solvent-extracted meal is less costly and allows a faster, more efficient fermentation due to better access of the relevant enzymes and organisms.

Whole beans or meal are soaked at room temperature (ideally 30°C) for 12-15 h such that there is a doubling of their weight. The water either flows continuously over the beans or is added batch-wise with changes every 2-3 h. This prevents heat accumulation and the development of spore-forming bacteria.

The swollen material is drained, re-covered with water and steamed to induce softening and afford pasteurisation. This is followed by rapid cooling to less than 14°C on 30-cm trays over which air is forced to avoid spoilage.

Table 14.1 A selection of indigenous fermented foods (see also Chapter 18).



Ang kak Asian colorant based on Monascus purpureus growing on rice

Bouza Thick sour wheat-based drink from Egypt

Burukutu Creamy turbid drink in Nigeria made by fermentation of sorghum and cassava by Saccharomyces, Candida and lactic acid bacteria Chichwangue Bacterial fermentation of cassava root in Congo, eaten as a paste Dosai Indian spongy breakfast pancake from black gram flour and rice, fermented by yeasts and Leuconostoc mesenteroides Idli Indian bread substitute, also from black gram and rice with fermentation by

Leuconostoc mesenteroides, Torulopsis candida, Trichosporon pullulans Jalebies Indian confectionery from wheat flour by Saccharomyces bayanus

Kaanga-kopuwai Fermented maize - soft and slimy - eaten as a vegetable Ketjap Indonesian liquid condiment from fermentation of black soybean by

Aspergillus oryzae

Lao-chao Glutinous dessert in China from rice fermentation by Chlamydomucor oryzae,

Rhizopus chinensis, Rhizopus oryzae, Saccharomycopsis sp. Ogi Breakfast food in Nigeria and West Africa made from corn (maize) -

fermentation by lactic acid bacteria, Aspergillus, Candida, Cephalosporium, Penicillium, Saccharomyces Poi Hawaiian side dish to accompany meat and fish made from Taro corms.

Relevant organisms: Candida vini, Geotrichum candidum, Lactobacilli Rabdi Semi-solid mush eaten with vegetables in India and made by fermentation of corn and buttermilk

Tapé Soft solid staple fresh dish in Indonesia made from cassava or rice with the aid of Chlamydomucor oryzae, Emdomycopsisfibuliger, Hansenula anomala, Mucor sp., Rhizopus oryzae, Saccharomyces cerevisiae

Table 14.2 Soy sauces recognised by the Japanese Government.











(gper 1OOmL)

(gper 100 mL)







Deep brown






Dark brown












Dark brown






Light brown

All the soy sauces have a pH in the range 4.6-4.8 and salt levels between 17.6 and 19.3 g per 100 mL. Derived from Fukushima (1979).

All the soy sauces have a pH in the range 4.6-4.8 and salt levels between 17.6 and 19.3 g per 100 mL. Derived from Fukushima (1979).

At the same time, wheat (or wheat flour or bran) is roasted to generate the desired flavour characteristics. Products include vanillin and 4-ethylguaiacol from the degradation of lignin and glycosides (Fig. 14.2). The degree of roasting will also impact the colour.

The word 'koji' means 'bloom of mould'. Koji for soy sauce (known as tane) involves the culture of mixed strains of Aspergillus oryzae or Aspergillus sojae on either steamed polished rice or (less frequently and in China) a mix of wheat bran and soybean flour. It is added to the soybean/wheat mix at 0.1-0.2% to produce koji. Important characteristics of the selected strains


Inoculate with Aspergillus 25-30°C, 2-5 days



Pasteurise, bottle

Fig. 14.1 Soy sauce production.

Fig. 14.1 Soy sauce production.

are the ability to generate high levels of several enzymes (protease, amylase, lipase, cellulase and peptidase) and they should favourably contribute to the aroma and flavour of the final product.

A 1 :1 soybean: wheat mixture is spread in 5-cm layers on bamboo (or steel) trays and inoculated with the koji starter. The trays are stacked such that there is good circulation of air, with control of the temperature in the range 25-35°C. Moisture control is important - a high level at first allows mycelial growth, but lower later when the spores are being formed. This stage takes some 2-5 days. Incubation is sufficient for enzymes to be developed, but not too prolonged because otherwise, sporulation occurs, which is accompanied by the development of undesirable flavours.



170-180°C, 10 min crush


Tetragenococcus halophila, Zygosaccharomyces rouxii, 6-8 months, press

Mash (moromi) stage

When the koji is mature, it is mixed with an equal volume of saline, with the target sodium chloride level being 17-19%. Less than that allows the development of putrefactive organisms. If the salt content is too high, there is an inhibition of desirable osmophilic and halophilic organisms. The salt destroys the koji mycelium.

Originally (and still at the craft level) fermentation is not temperature regulated and can take 12-14 months. On a commercial scale in wood or concrete fermenters, the temperature is controlled to 35-40°C for a period of 2-4 months. The must is mixed from time to time with a wooden stick on the small scale or with compressed air on the large scale. The enzymes of the koji hydrolyse proteins early in the fermentation process to generate peptides and amino acids. Then the amylases release sugars from starch, these being fermented to lactic, glutamic and other acids, causing the pH to fall to 4.5-4.8. Carbon dioxide is also produced. If this is in excess, then there is too much opportunity for anaerobic organisms to develop, with attendant flavour difficulties. Conversely, if there is excessive oxygen, then the fermentation does not proceed according to the desirable course.

The microbiology of soy sauce production is not fully appreciated. In the earliest stages, halophilic Pediococcus halophilus predominates, converting sugars to lactic acid and dropping pH; followed by Zygosaccharomyces rouxii, Torulopsis and certain other yeasts.

Table 14.3 lists some of the compounds that contribute to the flavour of soy sauce. Yeasts make the biggest contribution to the flavour of soy sauce, generating inter alia 4-ethyl guiaicol, 4-ethylphenol, ethanol, pyrazones, fura-nones, ethyl acetate. Acids are generated by Pediococcus and perhaps lactic acid bacteria.

Table 14.3 Some of the compounds that contribute to the flavour of soy sauce.

Acetaldehyde Acetic acid Acetoin Acetone 2-Acetyl furan

2-Acetyl pyrrole Benzaldehyde Benzoic acid Benzyl alcohol Borneol Bornyl acetate Butanoic acid

1-Butanol Diethyl succinate 2,6-Dimethoxyphenol 2,3-Dimethylpyrazine 2,6-Dimethylpyrazine Ethanol

Ethyl acetate Ethyl benzoate


4-Ethylguaiacol Ethyl lactate

2-Ethyl-6-methylpyrazine Ethyl myristate 4-Ethylphenol

Ethyl phenylacetate

Furfural Furfuryl acetate Furfuryl alcohol Guaiacol 2,3-Hexanedione







3-Methylbutanal 3-Methylbutanoic acid 3-Methyl-1-butanol 3-Methylbutyl acetate 2-Methylpropanal 2-Methylpropanoic acid


3-Methylpyrazine 3-methyl-3-tetrahydrofuranone

4-Pentanolide Phenylacetaldehydee 2-Phenylethanol 2-Phenylethylacetate Propanal 2-Propanol

Liquid is removed from the mash by pressing (hydraulic presses are used in large-scale operations) and new salt water may be added to the residue. A second fermentation may proceed for 1-2 months generating a lower quality product. Oil is removed from filtrate by decantation.

Raw soy sauce is pasteurised at 70-80° C to kill vegetative cells and denature enzymes. Alum or kaolin may be added as clarifiers before the product is filtered and bottled. Para-hydroxybenzoate or sodium benzoate may be added as antimicrobials.

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  • paride pugliesi
    What type of fermentation occurs in soy sauce?
    9 months ago

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