How is lactic acid bacteria used in soy sauce?

Lactic acid bacteria (LAB) play a vital role in the production of soy sauce, a traditional fermented condiment originating from East Asia. LAB are responsible for the fermentation process that transforms soybeans and wheat into soy sauce. Their metabolic activities contribute to the development of soy sauce's characteristic flavor, aroma, and texture.

Here's how lactic acid bacteria are used in soy sauce production:

1. Preparation of Koji:

The first step in soy sauce production involves preparing koji, a fermented mold culture. Soybeans are steamed and mixed with roasted wheat, and then inoculated with a koji starter culture containing Aspergillus oryzae or Aspergillus sojae spores. LAB are present naturally on these koji molds and start growing alongside them.

2. Fermentation:

The koji mixture undergoes fermentation, where LAB and koji enzymes work synergistically. LAB ferment the carbohydrates present in soybeans and wheat, converting them into lactic acid and other organic acids. This process gives soy sauce its characteristic sour flavor and helps preserve it.

3. Mashing and Extraction:

After fermentation, the koji mixture is mashed with brine and left to continue fermentation for several months. LAB and other microorganisms continue to break down proteins and carbohydrates, releasing amino acids, peptides, and sugars that contribute to soy sauce's rich flavor and umami taste.

4. Pressing:

The fermented mash is then pressed to separate the liquid (moromi) from the solids. LAB and other microorganisms remain in the moromi, contributing to its continued fermentation and flavor development during the aging process.

5. Aging and Maturation:

The moromi undergoes a prolonged aging period, typically lasting several months to years, in wooden barrels or stainless steel tanks. During aging, LAB continue to produce lactic acid and other compounds, further enhancing soy sauce's flavor complexity and mellowing its taste.

6. Refining and Packaging:

Once the soy sauce has aged and reached its desired flavor profile, it undergoes clarification, filtration, and pasteurization to remove any remaining microorganisms and ensure its stability and shelf life. After these final steps, the soy sauce is bottled and ready for distribution and consumption.

By utilizing the metabolic activities of lactic acid bacteria, soy sauce producers achieve the desired flavor, acidity, and preservation qualities that make soy sauce a versatile and flavorful condiment enjoyed worldwide.