Soy sauce is a very flavorful ingredient made from fermented soybeans and wheat.
It originated in China and has been used in cooking for over 1,000 years.
Today, it’s one of the best-known soy products worldwide. It is a staple ingredient in many Asian countries and used widely across the rest of the world.
The way it's produced can vary significantly, causing significant changes in flavor and texture, as well as health risks.
This article investigates how soy sauce is produced and its potential health risks and benefits.
Soy sauce is a salty liquid condiment traditionally produced by fermenting soybeans and wheat.
It is thought to have originated from a Chinese product called “chiang” over 3,000 years ago. Similar products were developed in Japan, Korea, Indonesia and across Southeast Asia.
The word “soy” comes from the Japanese word for soy sauce, “shoyu.” In fact, the soybean itself was named from soy sauce (1).
The four basic ingredients in soy sauce are soybeans, wheat, salt and fermenting agents like mold or yeast.
Regional varieties of soy sauce may have varying amounts of these ingredients, resulting in different colors and flavors.
Summary Soy sauce is a salty condiment produced through the fermentation of soybeans and wheat. It originated in China and is now produced in many Asian countries.
Many different types of soy sauce are available. They can be grouped based on their production methods, regional variations, color and taste differences.
Traditional soy sauce is made by soaking soybeans in water and roasting and crushing the wheat. Then the soybeans and wheat are mixed with a culturing mold, most commonly Aspergillus, and left for two to three days to develop.
Next, water and salt are added, and the entire mixture is left in a fermenting tank for five to eight months, though some types may age longer.
During fermentation, enzymes from the mold act on the soy and wheat proteins, gradually breaking them down into amino acids. The starches are converted to simple sugars, then fermented to lactic acid and alcohol.
High-quality soy sauce uses only natural fermentation. These varieties are often labeled “naturally brewed.” The ingredients list will usually only contain water, wheat, soy and salt.
Summary Traditional soy sauce is made with a mixture of soybeans, roasted wheat, mold and salt water, which is aged for five to eight months. The resulting mash is then pressed, and the soy sauce liquid is pasteurized and bottled.
Chemical production is a much faster and cheaper method of making soy sauce. This method is known as acid hydrolysis, and it can produce soy sauce in a few days instead of many months .
In this process, soybeans are heated to 176°F (80°C) and mixed with hydrochloric acid. This process breaks down the proteins in the soybeans and wheat.
However, the resulting product is less attractive in terms of taste and aroma, since many substances produced during traditional fermentation are missing. Therefore, extra color, flavor and salt are added (4).
Additionally, this process produces some undesirable compounds that are not present in naturally fermented soy sauce, including some carcinogens (2).
In Japan, soy sauce that is brewed in a purely chemical process is not considered soy sauce and cannot be labeled as such. However, it may be mixed with traditional soy sauce to lower costs.
In other countries, chemically produced soy sauce may be sold as-is. This is often the type of soy sauce you’ll find in the small packets given with take-away meals.
The label will list “hydrolyzed soy protein” or “hydrolyzed vegetable protein” if it contains chemically produced soy sauce.
Summary Chemically manufactured soy sauce is made by hydrolyzing soy proteins with acid and heat. This method is quick and cheap, but the resulting soy sauce tastes inferior, contains some toxic compounds and may require extra colors and flavors.
In Japan there are many different types of soy sauce.
- Dark soy sauce: Also known as “koikuchi shoyu,” this is the most common type sold in Japan and overseas. It’s reddish brown and has a strong aroma (2, 3, 5).
- Light soy sauce: Also called “usukuchi,” this is made from more soybeans and less wheat, and it has a lighter appearance and milder aroma (2, 3, 5).
- Tamari: Made from mostly soybeans with 10% or less wheat, it lacks aroma and is darker in color (3, 5).
- Shiro: Made almost only with wheat and very few soybeans, it's very light in color (3).
- Saishikomi: Made by breaking down the soybeans and wheat with enzymes in a solution of unheated soy sauce instead of salt water. It has a heavier taste, and many enjoy it as a dipping sauce (2, 3, 5).
In China, the tamari-style soybean-only soy sauce is the most common type.
However, today a more modern production method is most common. Soybean meal and wheat bran are fermented for just three weeks instead of several months. This method results in a very different flavor compared to traditionally produced soy sauce (2, 3, 6).
Chinese soy sauces are often listed as “dark” or “light” in English. Dark soy sauce is thicker, older and sweeter and used in cooking. Light soy sauce is thinner, younger and saltier, and it's more often used in dipping sauces.
In Korea, the most common type of soy sauce is similar to the dark koikuchi type in Japan.
However, there is also a traditional Korean soy sauce called hansik ganjang. It’s made only from soybeans and mainly used in soup and vegetable dishes (3).
In Southeast Asian countries like Indonesia, Malaysia, the Philippines, Singapore and Thailand, the tamari-style sauce is most commonly produced, but many local variations exist (2).
Other varieties include sauces thickened with sugar, such as kecap manis in Indonesia, or those with additional flavors added, such as shrimp soy sauce in China.
Summary There is a great variety of soy sauces across Asia, each with different ingredients, flavors and aromas. The most common type is Japanese dark soy, called koikuchi shoyu, which is made from naturally fermented wheat and soybeans.
Below is the nutritional breakdown for 1 tablespoon (15 ml) of traditionally fermented soy sauce (7).
- Calories: 8
- Carbohydrates: 1 gram
- Fat: 0 grams
- Protein: 1 gram
- Sodium: 902 mg
This makes it high in salt, providing 38% of the Recommended Daily Intake (RDI). While soy sauce has a relatively high amount of protein and carbohydrates by volume, it’s not a significant source of those nutrients.
It is these compounds in soy sauce that are often linked with its health risks and benefits.
Summary Soy sauce is high in salt, providing 38% of the RDI in 1 tablespoon. It contains more than 300 compounds that contribute to flavor and aroma. These compounds may also be associated with health risks and benefits.
Health concerns are often raised regarding soy sauce, including its salt content, presence of cancer-causing compounds and specific reactions to components like MSG and amines.
It Is High in Sodium
Soy sauce is high in sodium, commonly known as salt, which is an essential nutrient that your body requires to function properly.
However, high intakes of sodium are linked to increased blood pressure, especially in salt-sensitive people, and may contribute to the risk of heart disease and other diseases such as stomach cancer (8, 9, 10, 11).
For those looking to reduce their sodium intake, salt-reduced varieties of soy sauce, which contain up to 50% less salt than the original products, have been developed (2).
Despite its high sodium content, soy sauce can still be enjoyed as part of a healthy diet, especially if you are limiting processed food and mostly consuming fresh, whole foods with plenty of fruits and vegetables.
If you are limiting your salt intake, try a salt-reduced variety or simply use less.
Summary Soy sauce is high in sodium, which is associated with an increased risk of high blood pressure. However, it is lower in sodium than table salt, and sodium-reduced varieties are available. Soy sauce can be included as part of a healthy diet rich in whole foods.
Can Be High in MSG
It is a form of glutamic acid, an amino acid that contributes significantly to the umami flavor of foods. Umami is one of the five basic flavors in food, often found in what is called “savory” food (24, 25).
Glutamic acid is produced naturally in soy sauce during fermentation and thought to be a significant contributor to its appealing flavor. Additionally, MSG is often added to chemically produced soy sauce to enhance its flavor (2, 5, 26, 27).
In 1968, MSG became associated with a phenomenon known as “Chinese restaurant syndrome.”
Therefore, the presence of glutamic acid or even added MSG in soy sauce is probably no cause for concern.
Summary MSG and its free form, glutamic acid, are an important part of the appealing umami taste of soy sauce. Although MSG was once thought to cause headaches, recent reviews suggest this isn’t the case.
May Contain Cancer-Causing Substances
A group of toxic substances called chloropropanols can be produced during food processing, including the production of soy sauce.
This equates to a legal limit of 0.032–1.6 mcg per tablespoon of soy sauce, depending on where you live.
However, in recent years, investigations of soy sauce imports across the world, including in the US, UK, Australia and Europe, have found products significantly over the limits, with up to 1.4 mg per tablespoon (876 mg per kg), resulting in product recalls (30, 31, 33).
Overall, it is safer to choose naturally fermented soy sauce, which has much lower levels or no 3-MCPD at all.
Summary Chemically produced soy sauce contains a toxic substance called 3-MCPD. Across the globe, there have been multiple recalls of soy sauce products that exceed safe limits of the substance. It’s best to stick to naturally fermented soy sauce.
Amines are naturally occurring chemicals found in plants and animals.
They are often found in higher concentrations in aged foods, such as meats, fish, cheeses and some condiments (34).
Too much histamine is known to cause toxic effects when eaten in high quantities. Symptoms include headaches, sweating, dizziness, itching, rashes, stomach problems and changes in blood pressure (34, 36).
In fact, it has been suggested that some reports of soy sauce allergy may be due to a histamine reaction (37).
In most people, the other amines in soy sauce don’t appear to cause problems. However, some people can be sensitive to them. This is usually diagnosed through a supervised elimination diet. Symptoms of intolerance include nausea, headaches and rashes (34).
If you are sensitive to amines and experience symptoms after eating soy sauce, it may be better to avoid it.
Summary People who are sensitive to amines, including histamine, may want to reduce their intake of soy sauce or avoid it altogether. If you are taking an MAOI, you should avoid soy sauce due to its tyramine content.
Contains Wheat and Gluten
Studies have found that both soy and wheat allergens are completely degraded in the soy sauce fermentation process. That said, if you are not sure how your soy sauce has been produced, you cannot be sure it is free from allergens (40).
The Japanese soy sauce tamari is often regarded as a wheat- and gluten-free soy sauce alternative. While this can be true, some types of tamari may still be made with wheat, though with smaller amounts than are used in other types of soy sauce (3).
It is important to check the ingredients label for wheat and look for soy sauce products that are specifically labeled as gluten-free. Most major brands carry a gluten-free variety.
When you’re eating out, it’s best to double check what brand of soy sauce the restaurant is cooking with and ask if they have a gluten-free variety.
If you are unsure, it may be better to choose a dish not cooked with soy sauce.
Summary Soy sauce contains wheat and gluten, and even the tamari type may still contain some wheat. If you are allergic to wheat or have celiac disease, look for gluten-free soy sauce and always check the ingredients list.
Research on soy sauce and its components has found some potential health benefits, including:
- May reduce allergies: 76 patients with seasonal allergies took 600 mg of a soy sauce component per day and showed improved symptoms. The amount they consumed corresponds to 60 ml of soy sauce per day (40, 41).
- Promotes digestion: A soy sauce broth was given to 15 people, resulting in increased stomach juice secretion, similar to the levels that can occur after ingesting caffeine. Increased stomach juice secretion is thought to help digestion (42).
- Gut health: Some isolated sugars in soy sauce have been found to have a positive prebiotic effect on certain types of bacteria found in the gut. This could be beneficial for gut health (43).
- Source of antioxidants: Dark soy sauce has been found to contain several strong antioxidants. It is unclear what the benefits may be in humans, though one study found positive effects on heart health (44, 45, 46, 47).
- Could promote the immune system: Two studies found that giving mice polysaccharides, a type of carbohydrate found in soy sauce, improved immune system responses (48, 49).
- May have anticancer effects: Multiple experiments on mice have shown soy sauce may have cancer- and tumor-inhibiting effects. More research is needed to see if these effects are also present in humans (44, 50).
- May reduce blood pressure: Some varieties of soy sauce, such as salt-reduced or Korean ganjang, have been found to decrease blood pressure in mice. Studies in humans are still needed (44, 51, 52).
It should be noted that much of this research has only been done in animals or very small studies in people and used large doses of soy sauce or its components.
Therefore, while some of these results sound promising, it is too early to say whether soy sauce can contribute truly significant health benefits when it’s consumed at the level found in the average diet.
Summary Research on soy sauce has found promising potential health benefits, including for the immune system, gut health, cancer and blood pressure. However, since most studies have used animals or small sample sizes, more research in humans is needed.
Soy sauce is a flavorful condiment that is used in a wide variety of dishes and cuisines.
It can be produced through natural fermentation or chemical hydrolysis. Each production method leads to quite different flavor and health profiles.
Eating soy sauce may involve some health risks. However, the worst of these are associated with chemically produced varieties and can be avoided by using naturally fermented soy sauce.
Soy sauce may also have some health benefits, but more research is needed to confirm whether they apply to humans.
Overall, like most foods, soy sauce can be enjoyed in moderation as part of a healthy diet.