Miso and soy sauce have more qualities in common than they have differences, but the differences can affect how you use them. Ideally, you should have both in your kitchen. The SPICEography Showdown post below shows how they compare if you are trying to choose between them.
How does miso differ from soy sauce?
The first thing to consider is what goes into these two seasonings. Miso is mostly of soybeans but traditional producers may include other grains like rice, wheat, and millet. Most of the grain in modern Japanese miso is rice but non-traditional versions may contain corn or even chickpeas. Soy sauce also contains soybeans that are fermented along with grain, but the only grain used in the traditional versions is wheat.
Miso is not as salty as light soy sauce. There is also a very noticeable difference in consistency; miso is a paste while soy sauce is a liquid.
The three most common miso varieties are white, red, and mixed. Red miso is fermented for longer and contains more of the umami note along with higher salt content. White miso is sweeter and is not fermented for as long as red miso. Mixed miso is a combination of red and white varieties.
Most Chinese soy sauce that you find in the West can be broken down into three categories: light, dark and thick. Light soy sauce is the most common and has a reddish color and a very thin consistency. Dark soy sauce may have molasses added to give it a darker color along with cornstarch for extra body. Dark soy sauce may also have been aged for longer. Thick soy sauce will have additional sugar during fermentation along with more wheat. It may also be thickened with starch.
If your recipe calls for one, can you use the other?
Miso can provide the same umami flavor profile and saltiness that you would get from soy sauce, so it can make an excellent substitute in some contexts. Because soy sauce contains considerably more salt than miso, you will need to add more salt to your dish. How much salt you add depends on the type of soy sauce your dish requires. You will need to add more salt if you are using miso in place of light soy sauce than if you are substituting for dark.
The difference in texture is important as well. You will need to thin the miso out to get a liquid similar to soy sauce.
Soy sauce can make an effective miso substitute since it will provide the same umami and salty flavor. You will need to use less of the soy sauce since it is saltier than the miso. You should also use light soy sauce since it won’t affect the color of the dish as much as a darker variety.
The fact that the dish will be missing the creaminess of miso means that you will have to add something else to provide the body. Tahini is a good option.
When should you use miso and when should you use soy sauce?
Use miso for soups or mix it into batters for fried foods or salad dressings. Avoid boiling miso so that you preserve its probiotic benefits.
Use soy sauce in marinades and dipping sauces. You can also sprinkle it into soups and noodle dishes.