Course:FNH200/Projects/2022/Soy Sauce

Introduction and History

Soy sauce is a salty condiment, made from fermented soybeans and wheat, that is very commonly found in many kitchens. It can be used as a dip for food, such as sushi, or can be added as a salty flavouring during cooking.

Soy sauce’s history dates back to over 3000 years ago in China during the Han dynasty, and later became popular also in Japan, Korea, Indonesia, and across Southeast Asia. Soy sauce was introduced to Japan from China in the 7th century. When Buddhism came to Japan, they also brought over many soy products, including soy sauce. Japan began to export soy sauce in 1647, and the product was introduced in Europe by the Dutch East India Company. Production of soy sauce in North America started in 1908, by the Hawaiian Yamajo Soy Company. Soy sauce is now a popular kitchen ingredient all across the world and it is used in all different types of cuisines.

The name soy sauce came from the Japanese name of the product, “shoyu”. There are two main types of soy sauce: dark and light. And their use and production are not entirely the same. This will be discussed in more detail in later sections.

Figure 1. Soy Sauce

Producing and Processing

There are two types of processing methods for producing soy sauce: the conventional and bioreactor methods. Traditionally, spores of Aspergillus species which act as starter culture are added to cooked soybeans and wheat to produce koji through fermentation for 2 days. Then salt water is added to make moromi, a solid culture that is further fermented to produce soy sauce. During fermentation of moromi, Pediococcus halophilus and Zygosaccharomyces rouxii grows. Pediococcus halophilus is a bacteria that produces lactic acid, which decreases the pH, whereas Zygosaccharomyces rouxii, a yeast, produces alcohol and many aroma components. The conventional method is time consuming and it takes about 6 to 8 months for the moromi mash to complete fermentation and aging.

In order to make the production more efficient, the bioreactor method is built to shorten the time and it only takes about 2 days for the fermentation process to be completed. The main differences between bioreactor and conventional methods are that a continuous culture of koji is used and the fermentation of moromi takes place in the liquid state. After filtration of the moromi mash, salt, immobilized glutaminase, P. halophilus, Z. rouxii, and C. versatilis will be added to the liquid mixture to assist the fermentation process. Glutaminase is used to produce glutamic acid which enhances the umami and savory flavor of soy sauce. Similar to Z. rouxii, C. versatillis also produces phenolic compounds such as 4-ethylguaiacol which helps with preservation as well as producing that distinctive aroma of soy sauce.

Figure 2. Soy Sauce Maturation

Differences in Processing Between Light and Dark Soy Sauce

Figure 3. A Visual Comparison Between Light and Dark Soy Sauce

Light Soy Sauce

Light soy sauce is commonly used in general cooking and seasoning, especially in lighter coloured dishes. The name comes from its thin, light reddish brown colour and its opaque appearance. Light soy sauce should not be confused with reduced-sodium soy sauce. Even though light soy sauce appears lighter in colour and thinner, it is actually saltier than dark soy sauce.

Light soy sauce is produced by the pressing of fermented soy beans (and wheat for Japanese soy sauces). A double-fermented light soy sauce can be produced where the initial batch of light soy sauce is used as the brine for the next batch of soy sauce. This produces a product with a deeper flavour without increasing the salinity and is commonly used for dipping and stir-frying. A Japanese light soy sauce called Usukuchi shoyu is distinct as it has an assertive salty flavour with a slight sweetness and acidity. The sweetness and acidity is due to additives such as mirin, corn syrup, and vinegar.

Dark Soy Sauce

Dark soy sauce is commonly used for adding a caramel colour to dishes near the end of its preparation. It is mainly used in dishes that require a darker colour such as red-braised pork or soy sauce chicken. It has a darker colour and a thicker texture compared to light soy sauce. In terms of flavour, it is less salty compared to light soy sauce but has a slight sweet flavour to it.

Dark soy sauce is produced by adding molasses or caramel to achieve that darker colour, thicker texture, and sweeter flavour. Compared to light soy sauce, dark soy sauce is usually fermented for longer.

Chemical Reactions

Traditional Method

Brewing is the traditional method of making soy sauce, which involves 3 steps - koji-making, brine fermentation and refinement. More about the traditional method is described above in the Producing and Processing section.

Chemical Method

Non-brewed methods involve the artificial breakdown of soy proteins instead of fermenting, through chemical hydrolysis. It is a method commonly used by manufactures as the process takes much shorter time compared to traditional methods of brewing.

Soybeans are boiled in HCl acid for 15-20 hours to remove the amino acids from the soybeans. The mixture is then cooled to stop the hydrolytic reaction. Then, sodium carbonate is added to the amino acid liquid to neutralize it. It will be pressed through a filter to be mixed with active carbon and purified by filtration. Other ingredients such as corn syrup, salt, caramel color are then added to the mixture, for the final mixture to be refined and packaged.

Chemical methods of making soy sauce creates harsher flavour than the traditional method because the conversion is more complete in the chemical method, most of the proteins stay in the amino acid form as opposed to more complete peptides/proteins in the traditional method, and thus a different flavour. Soy sauce made from the traditional method also has different aroma and mouthfeel due to other compounds such as alcohols and esters.

Maillard reaction

Maillard reactions, non-enzymatic browning reactions, occur between amino groups in protein and reducing sugars at high temperatures, contributing to the colour and flavour of soy sauce.

Amadori compounds, formed from Schiff base formation during Maillard reactions, helps contribute to the umami taste. Kokumi, a proposed sixth taste that is described as a hearty and long lasting taste, can be contributed to certain peptides and lipid metabolism products. These lipid metabolism products also react with products of the Maillard reaction to give soy sauce its unique aroma profile of malty, caramel-like, roasted, and nutty scent.

Health Risks and Benefits

15mL (about 1 tablespoon) of soy sauce contains:

• 10 calories
• 2 grams of proteins
• 0 grams of fat
• 0 grams of carbohydrates
• 920mg of sodium (which is 38% of daily value)

Soy sauce is very high in its salt content. It also contains many byproducts that are produced during the fermentation process, such as alcohol, sugar, and many different types of acids. The concern with consuming large amounts of sodium would be that it can increase blood pressure, and thereby also increase the risk of cardiovascular diseases, such as heart attack and stroke.

Additionally, the contaminant 3-MCPD can be made if rapid fermentation or a mixed method is used to process the soy sauce, versus the traditionally brewed method. It is not well studied, and is a potential carcinogen.

Possible health benefits

Soy products contain isoflavones which are compounds with possible benefits towards reducing menopause symptoms and cholesterol. However, since soy sauce is consumed in small quantities, alternative soy products such as soy milk or tofu may be better options.

One study examining the antioxidant activity of seasonings used in Asian cooking revealed that dark soy sauce had an exceptionally high amount of antioxidant activity. Antioxidants are known to delay or prevent cell damage from free radicals. However, the evidence surrounding the antioxidant activity in soy sauce is limited and more studies will need to be conducted to verify this claim.

Exam Question

Choose all the correct options about the differences between light and dark soy sauce. [A&B]

A. Light soy sauce is saltier than dark soy sauce

B. Dark soy sauce is thicker and sweeter

C. Light soy sauce is fermented for a longer period of time than dark soy sauce

D. Light soy sauce is the same as reduced-sodium soy sauce

Explanation: See the first paragraph under light soy sauce and dark soy sauce respectively:

"Even though light soy sauce appears lighter in colour and thinner, it is actually saltier than dark soy sauce."

"In terms of flavour, it is less salty compared to light soy sauce but has a slight sweet flavour to it."

Which of the following descriptions of the production process of soy sauce is/are correct? [C]

A. Bioreactor and conventional methods both take about 6 months to produce soy sauce

B. A solid moromi culture is used in bioreactor method, whereas a liquid culture is used in conventional method

C. A liquid culture is used in bioreactor method, whereas a solid moromi culture is used in conventional method

D. P. halophilus and Z. rouxii both produce phenolic compounds to help with preservation and production of the distinctive aroma of soy sauce

Explanation: See the 2nd paragraph under producing and processing

" The main differences between bioreactor and conventional methods are that a continuous culture of koji is used and the fermentation of moromi takes place in the liquid state. "