The story and science of soy sauce

The original predecessors of soy sauce began to appear in China more than 2,500 years ago.  Salt was scarce and expensive at the time, and a method to extend salt was discovered by fermenting it with soy beans and fish.  During the Han dynasty around 220 BCE, Buddhism was beginning to expand into China from India.  One of the precepts for Buddhists includes refraining from harming living beings, and so the original fermented sauce was split into two different fermentation products to prevent monastic and lay practitioners from eating foods produced from animals – fish sauce, and soy sauce as the vegetarian alternative.

Soy sauce became prominent in Chinese Buddhist cuisine, as it was one of the few strong flavoring agents available that could be used to enhance the flavors of an otherwise relatively bland vegetarian diet.  Interestingly, highly pungent vegetables that are typically used to spice up cuisine, including onions, leeks, garlic, and shallots, were also abstained by monastics as they are said to overexcite the senses and increase sexual desire.  Near the end of the 7th century, Japanese Buddhist priests studying in China returned home and brought with them methods of soy sauce production along with the Buddhist teachings.  While accepted by the Japanese ruling class, these first groups of Buddhists were not particularly popular with the common people at the time due to its complexity.

Even though soy sauce arrived around the 7th century it has been cited that the popularity of soy sauce only arose in Japan after 1254 AD. That was when a Japanese Zen priest returned from China after learning to make a fermented miso-like soybean paste at a Chinese Zen temple and settled in the town of Yuasa, Japan.  He discovered that the liquid dredges of the miso made excellent cooking and dipping sauce, which was unique from the previous versions of soy sauce brought over centuries before.  The production method was shared and became the basis for modern Japanese soy sauces with their distinctive flavor.  At the same time, Buddhism began to flourish after less complex forms of the tradition were propagated to the common people.  Soy sauce development and production became an important activity conducted at these Buddhist temples.

Soy sauce is traditionally made using salt, water, soybeans, and wheat.  The soybeans are first steamed and the wheat toasted to provide the major foundations for soy sauce flavor.  The treated ingredients are crushed, boiled, and mashed together in equal proportions with water, cooled down to about 80 degrees Fahrenheit, then inoculated with a special edible filamentous mold known as koji.  Koji is composed primarily of Aspergillus oryzae, but most koji cultures contain some amount of other benign molds which add distinctive flavors to the soy sauce as well.  Different regions are known for their different koji strains, which impart flavors that reflect those areas of Japan.  The koji releases a suite of protease and amylase enzymes into the raw material mixture. The proteases cause the soy and wheat proteins to hydrolyze into amino acids and small peptides.  The amylases convert starches in the wheat into simple sugars, which provide energy for the koji to live and imparts sweetness to the soy sauce. 

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