Yes, all soy sauce contains glutamate, the compound that gives MSG its flavor. Naturally brewed soy sauce produces glutamate through fermentation, while some commercial soy sauces also add manufactured MSG as a separate ingredient. Either way, the savory “umami” taste you associate with soy sauce comes from the same molecule found in MSG.
How Fermentation Creates Natural Glutamate
Traditional soy sauce is made by fermenting soybeans and wheat with specific molds, then aging the mixture in brine for months. During this process, enzymes break down soy proteins into their building blocks: individual amino acids and small protein fragments called peptides. Glutamic acid, the amino acid responsible for umami taste, is one of the most abundant amino acids released.
The breakdown happens in stages. First, enzymes slice large soy proteins into smaller chunks. Then a second wave of enzymes chops those chunks into individual amino acids. A separate enzyme converts a related compound into glutamic acid specifically, which intensifies the savory flavor. This is the same molecule that makes up monosodium glutamate, just produced by microbes instead of a factory. Naturally brewed soy sauce with no added MSG typically contains between 9 and 35 milligrams of glutamic acid per milliliter. A single tablespoon holds roughly 15 milliliters, so even a modest splash delivers a significant dose of natural glutamate.
Added MSG in Commercial Soy Sauce
Some brands go a step further and add manufactured MSG on top of the glutamate already produced by fermentation. This is most common in cheaper soy sauces that use a faster chemical process (acid hydrolysis) instead of months-long brewing. Because fermentation wasn’t doing the work of building flavor, manufacturers compensate by adding MSG directly.
Research comparing the two types found that soy sauces with added MSG had higher glutamic acid concentrations than naturally brewed versions, but lower levels of other amino acids. In other words, the added-MSG products taste more one-dimensionally savory, while traditionally brewed soy sauce has a broader, more complex flavor profile because it contains a wider range of amino acids and peptides.
The quickest way to know which type you’re buying is to check the ingredient list. If MSG is added, it must be listed as “monosodium glutamate.” Brands like Kikkoman’s naturally brewed soy sauce typically contain only soybeans, wheat, salt, and water, with no added MSG. Many store-brand and budget options do include it.
Your Body Handles Both the Same Way
Chemically, the glutamate in naturally brewed soy sauce and the glutamate in a packet of MSG are identical. Your digestive system processes them the same way, and your taste receptors respond to them the same way. There is no physiological difference between “natural” and “added” glutamate once it reaches your bloodstream.
This matters because some people avoid soy sauce specifically to dodge MSG. The concern traces back to a 1968 letter in the New England Journal of Medicine describing symptoms after eating Chinese food. Since then, multiple controlled studies have failed to find a consistent link between MSG and the reported symptoms, which include headaches, flushing, and tingling. The FDA rates MSG as generally recognized as safe. In one FDA review, minor reactions only appeared when people consumed 3 or more grams of MSG alone, without food. Most foods with added MSG contain less than 0.5 grams.
A tablespoon of soy sauce, even one with added MSG, falls well below that 3-gram threshold. If you feel off after eating soy sauce-heavy meals, the sodium content (a single tablespoon packs around 900 milligrams of sodium) is a more likely culprit than the glutamate.
What “No MSG” Labels Actually Mean
FDA labeling rules require that added MSG appear on the ingredient list. But the agency also states that foods containing any ingredient that naturally contains MSG cannot carry a “No MSG” or “No added MSG” claim on the packaging. Since soy sauce inherently contains glutamate from fermentation, this creates an odd gray area. A naturally brewed soy sauce has no added MSG, yet technically shouldn’t advertise itself as MSG-free either, because the glutamate is already there.
For practical purposes, if you’re trying to minimize glutamate intake, switching from one soy sauce brand to another won’t make a dramatic difference. The glutamate is baked into what soy sauce fundamentally is. Reducing portion size or using a low-sodium version (which also tends to have slightly less glutamate) is a more effective strategy than hunting for an MSG-free label.