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【English Name】Lactic Acid Fermentation

Lactic fermentation (nyusan-hakko) is a metabolic reaction in which microorganisms or animal cells break down sugars in an oxygen-free environment to produce lactic acid. Chemically, two molecules of lactic acid are generated from one molecule of glucose.

In the history of sushi, lactic fermentation plays an extremely important role. Narezushi is a food in which salt-cured fish is pickled together with rice and gains tartness and preservability from the lactic acid produced by lactic-acid bacteria, and it is regarded as the prototype of present-day nigiri sushi. The funazushi of Shiga Prefecture is a representative example.

Lactic-acid bacteria are broadly classified by their mode of fermentation into two types: homofermentative bacteria, which produce lactic acid as their sole end product, and heterofermentative bacteria, which simultaneously produce alcohol, acetic acid, and other compounds. The complex flavor of narezushi is thought to involve such diverse fermentation products.

Lactic fermentation is widely used in food cultures around the world, including pickles, yogurt, sauerkraut, menma, and amazake. A common feature is that the lactic acid produced turns the surrounding environment acidic, suppressing the growth of spoilage bacteria and improving preservability. In the kimoto method of sake brewing as well, there is a process that uses acidification by lactic-acid bacteria to prevent the proliferation of unwanted microbes.