Soy Sauce

Soy sauce was shipped in barrels within Asia over 500 years ago, and in bottles to Europe by the 1600s. Now soy sauce is used all over the world. About 5000 years ago in China, people grew soybean crops for food and animal feed. Because soybeans spoil easily, salt was added as a preservative. Over time the beans fermented much like pickles or sauerkraut. Unlike pickles, however the soy beans turn into a paste called miso as they ferment. The paste is easier to digest than the unfermented soy beans, and people have been eating it for centuries. About 500 years ago, someone discovered that instead of discarding the sauce at the bottom of the barrels, they could use it for cooking. Thus, soy sauce was invented.

Unlike making wine from grapes, soy sauce brewing is performed in two stages:

  1. First, the soy beans are steamed and mixed with toasted crushed wheat. Fungi Aspergillus oryzae and Aspergillus sojae are added to the mixture to make koji (the first step in the soy sauce-making process) that is then left uncovered for a couple of days.
  2. Next, salt and water are added to koji to form a mash called moromi. Moromi is then put in airtight containers where it is allowed to ferment for at least 6 months. The mash is then squeezed to get the liquid soy sauce. Finally, the sauce is filtered, pasteurized, and tightly bottled for distribution.

In the koji phase of soy sauce production, the contents of the bean/wheat paste undergo a number of fungi changes. Once Aspergillus has broken down the macromolecules in the soybeans and wheat into monomers, the koji phase ends. Moromi is then made by mixing koji with water and enough salt to make a 16-20% concentrated salt solution, or brine. When brine is added, the populations of microbes found in koji change. Both lactic acid and ethanol are found in soy sauce after the moromi phase is complete. Lactic acid results from reduction, while ethanol results from oxidation   In the making of Soy sauce fermentation easily occurs without human intervention. For example, tiny breaks on the skin of ripened grapes allow entry of microbes. Fermentative yeasts thrive in the interior of the grape, which provides both the high concentration of sugars and low pH. Yeasts metabolize the grape sugars for energy, and the waste products—carbon dioxide and ethanol—are rapidly transported out of the cell. In an artificial fermentation, such as making wine, the process is carried out in a manner that permits CO2 to escape while preventing the entry of O2. There, alcohol continues to build up until the alcohol tolerance level of the specific yeast population is reached, ending the fermentation cycle.


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