How Long Miso Lasts In The Fridge (And Why It Stays So Fresh)

Have you ever tried to make miso soup at home? This Japanese dish is relatively easy to prepare, but you need the right ingredients. Some recipes call for dried kombu kelp, daikon, and other foods that are not widely available in grocery stores. What they all have in common is miso, a fermented soybean paste.

Centuries ago, miso was considered a luxury food reserved for the wealthy, according to the Umami Information Center. Back then, it was served as a side dish or used as medicine. The original recipe called for soybeans, salt, and koji, a fungus that aids in fermentation, and these ingredients are still used today. However, some grocery stores are now offering white, yellow, or red miso and other varieties with distinct flavors. For example, red miso paste is higher in salt than white or yellow miso, which gives it a stronger flavor, notes Bon Appétit.

Just like honey or sugar, miso paste can last for years when stored in proper conditions. Its shelf-life also depends on the ingredients used, among other factors. The question is, how long does it last in the fridge? And what's the best way to keep it fresh? Let's find out. 

As mentioned earlier, miso paste has just a few ingredients, including salt. Depending on the recipe, a teaspoon of miso provides around 634 milligrams of sodium, or 1.5 grams of salt, per the U.S. Department of Agriculture. Similarly, a serving of miso soup contains anywhere between 1 and 2 grams of salt, reports a 2019 study published in the journal Hypertension Research. This ingredient acts as a preservative, keeping food from spoiling.

According to Michigan State University, preservatives inhibit the growth of bacteria, fungi, and other pathogens in food. Moreover, these compounds may help prevent or slow oxidation, maintaining food color, texture, and flavor. Think about canned tuna, pickles, or brined cheese. These foods can last for months or years because of their high sodium content, and the same goes for miso.

Bon Appétit claims that miso can be kept in the fridge indefinitely, but its color and texture may change over time. Alternatively, you can place it in the freezer to maintain its appearance and flavor. However, its shelf-life ultimately depends on the ingredients used, especially the amount of sodium.

For example, white rice miso and low-sodium varieties will last approximately six months, whereas homemade rice miso can be stored for a year or longer, per Chef JA Cooks. Soybean miso and barley miso last more or less, depending on their composition.

Miso paste can be stored in the fridge or freezer, but you should first transfer it to an airtight container. You can also keep it in a dark, cool place if you plan to consume it over the next few weeks. Marukome, a Japanese manufacturer of miso products, recommends using plastic wrap to prevent oxidation after opening a can of miso.

Apart from that, watch out for any signs of spoilage, such as a sour taste, foul odors, or mold growth, notes Chef JA Cooks. Its color may become darker over time, which is a sign of oxidation. In this case, you can still use the miso paste. Also, note that miso continues to ferment while in the fridge, which may change its flavor. If that happens, add the paste to salad dressings, pickled tofu, stir-fried dishes, or mayo to mask its sourness.

For example, you can prepare a quick and easy miso vinaigrette by mixing the paste with low-sodium soy sauce, grape seed oil, sesame chili oil, rice wine vinegar, and other ingredients. Spread this mixture over grilled fish, root vegetables, turkey, or salads for a spicy kick.