Background

Soy sauce is the most popular fermented food in China, Japan and much of the rest of Asia. It is regarded as an indispensable culinary component, being used as a flavouring for an enormous range of dishes. It is acidic, salty, amino acid-rich and mildly alcoholic. The predominant amino acid present is glutamic acid; it is this component which is mainly responsible for the flavour enhancing properties of the sauce.

The widely used flavour-enhancing food additive monosodium glutamate is the synthetically derived sodium salt of this amino acid, whose organoleptic properties were originally recognised following the identification of its presence and role within soy sauce.

Although, as with other foods, soy sauce production processes differ in detail, all incorporate fermentation principles similar to those involved in both yoghurt manufacture and also brewing. The product is nutritionally valuable, versatile and in widespread use.

Soya beans soaked, then pressure-cooked

Resulting mash mixed with flour derived from roasted wheat

Culture of the fungus Aspergillus oryzae added

STAGE 1: Incubated for 3 days at 30°C

Mixture heavily salted

STAGE 2: Incubated in deep tanks for 3-6 months at 15°C, rising to 25°C

Left to 'age' for another 4-5 months

Solids filtered off, liquid collected

Liquid pasteurised, filtered again, then soy sauce bottled

Students should have an understanding of the processes occurring during each of the two main fermentation processes, only along the following lines:

• Stage 1 Aspergillus oryzae grows under aerobic conditions, releasing the enzyme amylase. This breaks down starch molecules into (smaller) sugar molecules. Proteins are also digested, again yielding smaller molecules. The products of both processes are used as food by yeast and other microorganisms in the second stage.
  

• Stage 2 The conditions in the deep fermentation tanks are ideal for the growth and reproduction of lactic acid bacteria which, as in yoghurt production, produce lactic acid and cause the pH to drop. Also, yeasts are active, producing alcohol.