Course:FNH200/Projects/2024/Japanese Shoyu

Japanese Shoyu (Traditional Shoyu)

Introduction and History

Japanese soy sauce, known as shoyu, spans many centuries and is an important part of Japan's food culture. It started in the Nara period (710-794 AD), evolving from a fermented seasoning called "hishio," which was a mix of grains, salt, and soybeans. This method likely came from China, where soy sauce had been used since the Han dynasty.

The state of soy sauce production, depicted in the “Koueki Kokusankou Kan-no-go” in the late Edo period (1603-1867). (National Diet Library, Japan)

During the Muromachi period (1336-1573), soy sauce became more popular. By the Edo period (1603-1868), production methods became more refined, involving the fermentation of boiled soybeans with roasted barley, salt, and water. This mixture was left to ferment then pressed to extract the liquid used as seasoning. In the Edo period, soy sauce production became a major industry, with different regions developing unique styles. The switch from barley to wheat in soy sauce production happened gradually during the Edo period. Wheat eventually became the preferred grain for better flavour production. By the 18th century, wheat had largely replaced barley. Soy sauce became an important export product in the Edo period. It was shipped to the Netherlands as early as 1668. European traders noted that Japanese soy sauce was of higher quality than Chinese versions, making it popular in Europe and other parts of Asia.

Ingredients and Nutrition

Shoyu is made using five basic ingredients:

1. Soybeans/soybean flakes - Protein: broken down by the protein-breaking enzyme protease from koji, produces amino acids that make the umami constituents.
2. Wheat/wheat flour - Carbohydrate: converted to glucose by amylase from koji, generating sweetness and depth.
3. Salt - Dissolved in water, base of the salty taste and suppresses putrefactive bacteria.
4. Koji mold (Aspergillus oryzae/sojae) - Fermentation starter.
5. Optional: Amino Acid Liquid and Alcohol - Using rice, umami seasonings such as amino acids or sweeteners and preservatives, flavor profiles can vary (e.g. sweeter, deeper etc.).

Shoyu is notably high in sodium, with 15 mL containing 960 mg which is 41.7% of the daily intake for sodium in Canada - which can pose health risks like high blood pressure which lead to stroke and heart disease if consumed in higher quantities. Though, sodium and acids constituents help food keep longer - they stop the proliferation of, or eliminate, E. coli bacteria. Shoyu also offers antioxidant properties, is low-calorie and provides essential amino acids.

KIKKOMAN Traditional Koikuchi Shoyu

Shoyu Nutritional table

Five Main Types of Shoyu

Koikuchi-shoyu Japanese dark soy sauce	Dark Shoyu	Shiro-shoyu White soy sauce (low soybean)	White Shoyu
Usukuchi-shoyu Japanese light soy sauce	Light Shoyu	Tamari-shoyu Tamari soy sauce (low wheat)	Tamari Shoyu
	Saishikomi-shoyu Double-fermented soy sauce	Saishikomi Shoyu

Uses

Shoyu is one of the main seasonings used in Japanese cuisine to add a salty and umami flavor. Commonly served as a dipping sauce for sushi, meat, vegetables and more. It is used to add flavor to soups, stews, and marinades or as a base for other Japanese sauces. Lighter soy sauces enhance the flavors of whitefish, simmered dishes, while umami-rich soy sauces pair better with meat and tuna.

Production Process for Shoyu

1. Inspect, wash, soak the soybeans

Dried beans are inspected for discoloration, mold and rocks. The beans are washed removing dust, debris or loose hulls then soaked to hydrate and accelerate subsequent cooking.

With soaking, the removal of natural fungal inhibitors is facilitated and a community of microorganisms including Lactobacillus casei grows, lowering pH to a 4.0-5.0 range.

2. Cook the soybeans

The wheat is roasted and crushed, then mixed in with the soybeans.

Soaked beans are drained and either pressured cooked, steamed or boiled to fully cooked. Aiming for beans that can be handled without crumbling but yields easily to a compression test.

Cooking hydrates starches and denatures proteins. Due to high heat the microorganism count is drastically reduced but the beans remain acidified.

3. Toast the wheat

Wheat kernels are inspected for debris or spoilage and toasted or roasted to a deep colour for most shoyu styles.

The toasting process creates new flavours, aroma and colouring impacting the profile of the final product. The heating also reduces the microorganism load of the wheat, which allows the inoculate to dominate during incubation.

4. Grind the wheat

The toasted kernels are crushed or ground exposing the germ and increasing surface area. The crushed wheat and cooled beans are mixed, with finer bits coating the beans.

5. Inoculate the mixture with koji spores

The soybean/wheat mixture is inoculated with koji mould spores, while gently stirred to improve dispersion. Dosing rates for the koji spores of 0.05-0.3% ensure that Aspegillus sojae or A. oryzae outcompete other microbes for dominance in the substrate.

6. Incubate the koji spores

Koji mold creates enzymes which help to change the proteins in soy beans to amino acids and the starch in wheat to glucose.

The inoculated substrate is kept warm and humid for typically 48-72 hours but ranging from 26h-7d. Koji spores will produce both amylase that begins breaking down polysaccharides into simple sugars and protease that begins hydrolyzing proteins into amino acids and peptides. The fungal growth of mycelia also generates heat. The beans are mixed periodically to ensure even growth, oxygenate the mould and disperse any heat pockets building up in the beds.

While the lowered pH of the beans initially limits the range of other microbes able to establish as part of the community, the fungal growth raises the pH to typically the 6.5-7.3 range. At this point koji should be established as a dominant microbe, suppressing the growth of many microorganisms.

7. Add koji mass to brine

Once sufficient fungal growth and growth of associated enzymes is achieved, the mass is transferred to a vessel and a brine solution of 18-22% NaCl is added. The mixture is carefully stirred to break up matted chunks and ensure relatively even hydration.

The high salt concentration and relatively low oxygen level of the brine solution ends the growth and enzymatic activity of the koji mould. Many microorganisms are unable to tolerate the new aqueous, low oxygen, high salt environment and die off.

8. Early ferment

The moromi (fermenting mash) is created by adding saline water to the koji.

During the first few weeks to months of fermentation, the mixture is stirred regularly and there is a shift in the microbial ecology of the moromi. Halotolerant lactic acid bacteria establish and begin lowering the pH down to a range of 4.0-5.0. Tetragenococcus halophilus has been determined to be a major contributor at this stage but other microbes including Lactobacillus raffinolactis, Weisella kimchii, Pediococcus acidilactici, Lactobacillus fermentum, Staphylococcus xylosus, and others may be present.

Despite non-sterile mash conditions, the dropping pH combined with the salt concentration and aqueous conditions limits the ability of many other microorganisms to propagate while creating a new environment favourable to others.

9. Later ferment

Later stages of the ferment occur under more acidic conditions. Yeasts, more easily grown in this environment, begin metabolising sugars into alcohols, negatively impacting conditions for bacteria, driving populations to decrease. Zygosaccharomyces rouxii is in antagonism with T. halophilus but other microbes making up the ecology may include Geotrichum silvicola, Wickerhamomyces anomalus, Trichosporon japonicum, Zygosaccharomyces pseudorouxii, Candida versatilis, Pichia anomala, and others. The overall diversity in moromi decreases as fewer organisms thrive in the aqueous, high salt, low pH and now alcoholic environment.

Extracting the soy sauce from the moromi in the Marushinhonke factory, fermented in cedar barrels.

10. Press the end product

Once a desired flavour profile is reached, moromi is transferred to a press and gradually increasing pressure is applied. Separating the shoyu from the solid moromi residue.

11. Filtration

The pressed liquid is filtered to remove any sediment, foreign material potentially introduced or soybean oil produced, as it will go rancid negatively impacting the flavour profile of the end product.

12. Pasteurization

The post filtration shoyu is heated to 70-80 C for 30 minutes. This increases the depth of colour via concentration, caramelization and Maillard browning. Additional aroma compounds such as 4-hydroxy-2, 5-dimethyl-3(2H)-furanone and 4-hydroxy-2-ethyl-5-methyl-3(2H)-furanone are generated during the Maillard reaction. Caramel or other additives may be added at this stage.

During the heating process pasteurises the product, eliminating both beneficial and harmful microorganisms, arresting the fermentation process.

13. Packaging

Following pasteurisation the cooked soy sauce is packaged in glass bottles, plastic or metal containers or individual serving packages. The packaging protects the soy sauce from oxygen until opening. After opening, it starts to oxidize due to contact with the air, so it must be kept closed and stored in a cool, dark place. This prevents yeast growth, at home it is best to refrigerate .

Exam Question

Prior to pasteurisation, what prevents spoilage of soy sauce?

(a.) High salt levels

(b.) Microbial antagonism

(c.) Lower pH

(d.) a&b

(e.) a&c

(f.) All of the above

Answer: (f.) All of the above

Explanation: Soy sauce's shelf stability is due to three key factors. The high salt levels in the brine inhibit the growth of most microorganisms. Microbial antagonism occurs as specific microbes dominate and out-compete others, preventing spoilage. Additionally, the fermentation process lowers the pH to a range of 4.0-5.0, which also helps stop harmful bacteria from growing. Together, these factors ensure that soy sauce remains stable and safe for a long time. This exam question touches on pH/acidic foods and bound water/water activity covered in Lesson 5, thermal processing/pasteurization covered in Lesson 6 and microbial antagonism covered in Lesson 9 on Biotechnology. It is a good question for bridging knowledge between multiple classes.