Soy sauce: How it's made, benefits, and potential health risks

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 is used widely across the rest of the world.

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How it’s produced can vary significantly, causing significant changes in flavor and texture and health risks.

This article investigates how soy sauce is produced and its potential health risks and benefits.

In this article

What is soy sauce?

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 Southeast Asia.

It first came to Europe in the 1600s through Dutch and Japanese trading.

The word “soy” comes from the Japanese word for soy sauce, “shoyu.” The soybean itself was named after soy sauce.

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.

How is soy sauce made?

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 production

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 to develop for two to three days.

Next, water and salt are added, and the 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.

After aging, the mixture is laid out onto a cloth and pressed to release the liquid. This liquid is then pasteurized to kill any bacteria. Finally, it’s bottled.

High-quality soy sauce uses only natural fermentation. These varieties are often labeled “naturally brewed.” The ingredients list usually only contains water, wheat, soy, and salt.

Summary: Traditional soy sauce is made with a mixture of soybeans, roasted wheat, mold, and salt water, aged five to eight months. The resulting mash is pressed, and the soy sauce liquid is pasteurized and bottled.

Chemical soy sauce production

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 regarding taste and aroma since many substances produced during traditional fermentation are missing. Therefore, extra color, flavor, and salt are added.

Additionally, this process produces some undesirable compounds not present in naturally fermented soy sauce, including carcinogens.

In Japan, soy sauce 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 soy sauce in the small packets with takeaway meals.

Regional differences

In Japan, there are many different types of soy sauce.

Dark soy sauce: Also known as “koikuchi shoyu,” the most common type sold in Japan and overseas. It’s reddish-brown and has a strong aroma.
Light soy sauce: Also called “usukuchi,” this is made from more soybeans and less wheat, with a lighter appearance and milder aroma.
Tamari: Made from mostly soybeans with 10% or less wheat, it lacks aroma and is darker in color.
Shiro: Made almost only with wheat and very few soybeans, it’s very light in color.
Saishikomi: Made by breaking down the soybeans and wheat with enzymes in a solution of unheated soy sauce instead of salt water. It tastes heavier, and many enjoy it as a dipping sauce.

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 three weeks instead of several months. This method produces a very different flavor than traditionally produced soy sauce.

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 is 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 is mainly used in soup and vegetable dishes.

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.

Suggested read: 6 brilliant oyster sauce substitutes

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.

The nutrient content of soy sauce

Below is the nutritional breakdown for 1 tablespoon (15 ml) of traditionally fermented soy sauce.

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. While soy sauce has a relatively high amount of protein and carbohydrates by volume, it’s not a significant source of those nutrients.

In addition, the fermentation, aging, and pasteurization processes result in a highly complex mix of more than 300 substances that contribute to soy sauce’s aroma, flavor, and color.

These include alcohols, sugars, amino acids like glutamic acid, and organic acids like lactic acid.

The amounts of these substances change significantly depending on the base ingredients, the mold strain, and the production method.

These compounds in soy sauce are often linked with their health risks and benefits.

Summary: Soy sauce is high in salt, providing 38% of the recommended daily intake 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.

What are the health risks of soy sauce?

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.

Soy sauce is high in sodium

Soy sauce is high in sodium, commonly known as salt, an essential nutrient your body requires to function properly.

However, high intakes of sodium are linked to increased blood pressure, especially in salt-sensitive people. They may contribute to the risk of heart disease and other diseases such as stomach cancer.

Reducing your sodium intake results in a modest decrease in blood pressure and can be part of a treatment strategy for people with high blood pressure.

However, it is unclear if reduction directly lowers the incidence of heart disease in healthy people.

Most dietary organizations recommend 1,500–2,300 mg of sodium daily to reduce the risk of high blood pressure.

One tablespoon of soy sauce contributes 38% of the recommended daily intake. However, the same amount of table salt would contribute 291% of the recommended daily sodium intake.

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.

Despite its high sodium content, soy sauce can still be enjoyed as part of a healthy diet, especially if you limit processed food and consume fresh, whole foods with plenty of fruits and vegetables.

If limiting your salt intake, try a salt-reduced variety or use less.

Summary: Soy sauce is high in sodium, 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 in a healthy diet rich in whole foods.

Soy sauce can be high in monosodium glutamate

Monosodium glutamate (MSG) is a flavor enhancer. It’s found naturally in some foods and often used as a food additive.

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 “savory” food.

Glutamic acid is produced naturally in soy sauce during fermentation and is thought to be a significant contributor to its appealing flavor. Additionally, monosodium glutamate is often added to chemically produced soy sauce to enhance flavor.

In 1968, monosodium glutamate became associated with a phenomenon known as MSG symptom complex.

Symptoms included headaches, numbness, weakness, and heart palpitations after eating Chinese food, often high in MSG.

However, a 2015 review of all studies on monosodium glutamate and headaches did not find significant evidence to suggest that MSG causes headaches.

Therefore, the presence of glutamic acid or even added monosodium glutamate in soy sauce is probably no cause for concern.

Summary: Monosodium glutamate 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.

Soy sauce may contain cancer-causing substances

A group of toxic substances called chloropropanols can be produced during food processing, including soy sauce production.

One type, 3-MCPD, is found in acid-hydrolyzed vegetable protein, which is found in chemically produced soy sauce.

Animal studies have found 3-MCPD to be a toxic substance. It was found to damage the kidneys, decrease fertility and cause tumors.

Due to these problems, the European Union set a limit of 0.02 mg of 3-MCPD per kg (2.2 lbs) of soy sauce. In the US, the limit is higher at 1 mg per kg (2.2 lbs).

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 worldwide, 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.

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 the safe limits of the substance. It’s best to stick to naturally fermented soy sauce.

Soy sauce contains amines

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.

Soy sauce contains significant amounts of amines, including histamine and tyramine.

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.

It has been suggested that some reports of soy sauce allergy may be due to a histamine reaction.

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.

If you are sensitive to amines and experience symptoms after eating soy sauce, it may be better to avoid it.

Additionally, people taking a class of medication known as monoamine oxidase inhibitors need to restrict their tyramine intake and should avoid soy sauce.

Summary: People sensitive to amines, including histamine, may want to reduce their intake of soy sauce or avoid it altogether. If you take monoamine oxidase inhibitors, you should avoid soy sauce due to its tyramine content.

Soy sauce contains wheat and gluten

Many people are unaware that soy sauce can contain both wheat and gluten. For people with wheat allergies or celiac disease, this could be problematic.

Studies have found that soy and wheat allergens completely degrade in the soy sauce fermentation process. That said, if you are unsure how your soy sauce has been produced, you cannot be sure it is free from allergens.

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 those used in other soy sauce types.

It is important to check the ingredients label for wheat and look for soy sauce products labeled 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, choosing a dish not cooked with soy sauce may be better.

Summary: Soy sauce contains wheat and gluten; 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.

Soy sauce is also linked to some health benefits

Research on soy sauce and its components has found some potential health benefits, including:

Soy sauce 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.
Soy sauce 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.
Gut health: Some isolated sugars in soy sauce has been found to have a positive prebiotic effect on certain types of bacteria found in the gut. This could be beneficial for gut health.
Soy sauce is a great 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.
Soy sauce could promote the immune system: Two studies found that giving mice polysaccharides, a carbohydrate type, improved immune system responses.
Soy sauce 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 also exist in humans.
Soy sauce 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.

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 the immune system, gut health, cancer, and blood pressure. However, more research on humans is needed since most studies have used animals or small sample sizes.

Summary

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 are associated with chemically produced varieties and can be avoided 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.

Like most foods, soy sauce can be enjoyed in moderation as part of a healthy diet.