Ingredients and production types
Soy sauce is made using essentially five basic raw ingredients: soybeans or soybean flakes as the main protein source, wheat or wheat flour as the main carbohydrate source, salt, water, and Aspergillus oryzae or Aspergillus sojae together with salt-tolerant yeast and lactic acid bacteria. There are essentially two general production processes: traditional fermentation and acid hydrolysis. Acid-hydrolyzed soy sauce can be produced in just a few days.
Brewing styles
High-salt liquid-state fermentation is generally carried out at 15-30 °C and requires a long ageing period, usually from 90 to 180 days. A high salt concentration of 17-20% is required to selectively inhibit microbial activity. Low-salt solid-state fermentation employs pure cultures at a relatively higher temperature, 40-55 °C, and lower brine concentrations of 13-15%. Low-salt solid-state fermentation has a short aging period of 15-30 days.
Taste
The saltiness is largely attributed to the NaCl in the brine. Sugars hydrolyzed from starch add sweetness. Umami is largely caused by free amino acids, mainly glutamine and aspartic acid. Sodium from the brine and disodium ribonucleotides from the soy also add to the umami. Umami, or savoriness, is one of the five basic tastes. Soy sauce is among the foods rich in umami components.
Aroma chemistry
During brewing, the Aspergillus mold on the soy and wheat breaks down the grain proteins into free amino acids and protein fragments, and the starches into simple sugars. This amino-glycosidic reaction gives soy sauce its dark brown color. Lactic acid bacteria ferment the sugars into lactic acid and yeast makes ethanol, which through aging and secondary fermentation makes numerous flavor compounds typical of soy sauce. The yeast Zygosaccharomyces rouxii, used in the fermentation of soybeans for soy sauce and miso, is important to the development of aromas.
HEMF is considered an important flavor contributor to soy sauce and is very stable in it. HEMF has also been reported in cheese, coffee, wine and miso. Furanones such as HDMF and HEMF have been identified as intense caramel-like aroma compounds in soy sauce. These furanones can be formed through Maillard reactions involving pentoses upon heating. HDMF and HEMF also occur naturally in different yeast species and are mainly associated with carbohydrate metabolism in Z. rouxii. Maltol is another potent caramel aroma compound found frequently in soy sauce. It has been detected in steamed soybean but not in raw soybean, and is therefore considered to originate from heating the soybeans before koji fermentation.
More than 60 aroma-active compounds have been identified in Japanese soy sauces, and more than 50 in Chinese ones. Among the more than 60 aroma-active compounds found in Japanese soy sauces, some, including guaiacol, 4-ethylguaiacol, 2- and 3-methylbutanal, methional, DMHF and HEMF, have a higher detection frequency in the analyzed samples. Dimethyl trisulfide is among the substances identified as aroma-active in all the Chinese soy sauce samples examined. Alcohols and esters dominate the volatiles of traditionally fermented soy sauces, whereas heterocyclic compounds such as pyrazines and furans, and acids, are relatively abundant in acid-hydrolyzed ones. Esters such as ethyl acetate and phenols such as guaiacol and 4-ethylguaiacol were found at relatively high levels in Japanese soy sauces compared with Chinese ones. Japanese soy sauces also contained higher levels of ethanol, 2-phenylethanol and phenylacetaldehyde, whereas the Chinese low-salt solid-state type scored higher for 3-methylbutanal, methional, dimethyl disulfide and 5-methyl-2-furancarboxaldehyde. In a pure soy sauce sample, ethanol was the most abundant compound, at approximately 60% of the total volatiles.
History
Soy sauce took its current form about 2,200 years ago, during the Western Han dynasty of ancient China.
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Related: Acetyl Furan · Ambermax · Ambrofix · Egg · Ethyl Maltol · Flour · Furfural · Genepi
