Characterizing Soy Sauce

Brewed soy sauce has almost 300 identifiable constituents. These constituents work together as a team to create flavor and aroma. They are the direct result of several reactions that take place concurrently during the extended fermentation step.

Salt: The brine added at the beginning of fermentation contributes saltiness. The finished salt concentration of regular traditionally brewed soy sauces range from 12.0 to 18.0%. But the salt isn't only there for flavor -- it is essential to the process. If, for example, the added salt level was reduced, the lactic acid bacteria and yeast in the moromi would act differently, resulting in a product with a very different flavor profile. The salt concentration is also necessary to help protect the finished sauce from spoilage.

Amino Acids: Enzymes denature the soybean protein into amino acids such as glutamic acid, aspartic acid, lysine, alanine, glycine, tryptophan and peptides. These acids and peptides not only contribute a full, robust flavor, but many can also act as flavor potentiators. Brewed soy sauce contains between 1.5% and 1.65% total nitrogen (weight per volume), with glutamic acid being the predominant one.

Sugar: The moromi enzymes also convert the wheat starch into sugars. Adequate sugar development is important to the finished soy sauce because it subdues the saltiness. Although glucose is the primary sugar, more than 10 others have been isolated. Yeast acts upon a portion of the sugars to form alcohol. Ethanol is the predominant of these and imparts many flavoring and aromatic characteristics. It also indicates the presence of other aromatic compounds produced by fermentation. However, ethanol content varies depending on the type of soy sauce. In tamari sauce, for example, the lower levels of wheat don't contribute enough starch to create ethanol, so its flavor profile is entirely different.

Color: Some of the amino acids and some of the sugar subsequently undergo a Maillard reaction to develop the sauce's characteristic reddish-brown color during fermentation. If finished soy sauce is exposed to oxygen, its color will darken undesirably. To protect both the flavor and color, opened containers of soy sauce should be sealed and refrigerated to control this reaction.

Acids: Part of the alcohols and an additional portion of the sugar react to produce acids. Finished soy sauce has a pH of about 4.8 and contains around 1.0% lactic acid. This contributes refined, rounded tartness that is believed to be one of the keys to good soy sauce flavor. In addition to lactic acid, more than 10 other organic acids may also be identified, including succinic. The acids act both as flavorings and as natural preservatives.

Aromatic Esters: Ethanol, once again, is critical because it combines with some of these organic acids to form esters; the same esters that give wines their bouquets. Without this reaction, virtually all of the aroma component of the soy sauce would be missing. Because the sense of smell is so critical to taste, the importance of the alcohol content is clear.

Post-Fermentation Development: While much of brewed soy sauce's unique flavor can be attributed to the extended fermentation process, the refining process is also critical. The heat of pasteurization further develops large numbers of compounds that contribute to aroma and flavor. At the same time, this step deepens the sauce's reddish-brown color. Of course, pasteurization improves stability by inactivating most of the enzymes and by producing organic acids and phenols to inhibit the growth of microorganisms.