Monitoring Japanese Soy Sauce Color via Spectrophotometry


Posted on September 5, 2017

“My mother always kept a gallon of Kikkoman Soy Sauce in the kitchen cubby,” writes Jenny Lee-Adrian. Whether preparing marinades, dipping sauces, or fried rice, the Kikkoman was an ever-present part of cooking in Lee-Adrian’s household. It wasn’t until years later, when she began cooking for herself that she realized there was a world of Japanese soy sauces out there beyond her mother’s beloved Kikkoman and these sauces can “vary wildly in flavor, texture, and appearance.”1

Indeed, as Florence Fabricant wrote over 20 years ago, “Soy sauce has many personalities. Its saltiness can vary from breathtakingly intense to mellow and muted. Its consistency ranges from watery to viscous.”2 This diversity makes Japanese soy sauces ideally suited for a broad variety of uses, whether you’re looking for a dark saishikomi or a light usukuchi. The varied usability of soy sauces combined with an increased propensity of consumers to eat at home and a growing body of research confirming the health benefits of soy help to explain why the soy sauce market is forecasted to increase significantly in the coming years.3

As the soy sauce market expands and consumers become more informed about soy sauce options, manufacturers must remain vigilant in monitoring the quality of their products to ensure they meet both industry and customer standards. As such, integrating spectrophotometric color measurement is an increasingly vital part of soy sauce production, even for those companies using time-honored, traditional methods of manufacturing.

The Creation of Soy Sauce Color

Soy sauces come by their color in a variety of ways. Many American manufacturers, for example, eschew traditional manufacturing methods in favor of “mixing soy protein with water, corn syrup, salt, and caramel color.” This produces a harsh and unappealing products that have little in common with fine soy sauces produced by Japanese companies. The highest quality soy sauces, on the other hand, use no artificial colorants. Instead, their trademark hues are entirely the natural result of traditional ingredients and fermentation-based processing methods. According to Kikkoman, one of the most renowned producers of soy sauce in the world:

The superb color unique to soy sauce is the result of the Maillard Reaction, which begins two or three months after brewing starts. In this reaction, glucose and other sugars combine with amino acids to produce a brown pigment called melanoidin. which gives soy sauce its beautiful color.4  

In other words, soy sauce grows darker as oxidation occurs, which means that manufacturers must carefully monitor processing to reach the desired level of coloration naturally, without resorting to artificial colorants. Although raw ingredient ratios and processing methods vary depending on the type of soy sauce being produced, the Maillard reaction is a primary component of color production in all soy sauce types.

Soy Sauce Color as an Indication of Quality and Usability

The Maillard reaction, however, doesn’t just affect color; it also has a significant impact on taste and aroma. As such, color in high-quality soy sauces isn’t simply a matter of aesthetics, but also acts as an important indicator of overall quality and usability. In fact, color is so important that it is perhaps the most important criteria used by the Japanese Soy Sauce Association to determine soy sauce grade.

Soy sauce grade and color have a deep impact on consumer perception, saleability, and product use. While koikuchi, a darkly colored sauce, is by far the most popular soy sauce in Japan, the lighter-colored usukuchi sauce is preferred by many in the Kyoto region. As Makiko Itoh points out, “In traditional Kyo-ryori (Kyoto cuisine), which has its origins in refined imperial court cooking, dark colored koikuchi soy sauce is considered déclassé and ruins the flavor and appearance of food.”5 Manufacturers must adjust their processing methods to achieve the precise kind and quality of soy sauce they are seeking, whether they are looking to produce tamari, which gives dishes a “burnished reddish-brown color and shine” or shiro, which adds flavor but not color.

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