You already know that miso(味噌) is used to make miso soup, a staple in Japanese cuisine. But do you know the expiration date of miso, how to store it, or how to know if your miso has gone bad?
Author: Asami Goto is a certified miso expert and bilingual Japanese food writer based in Tokyo. (edited and photos by Matt Eisenhauer)
Good news! In this post, you'll learn everything you need to know about miso's best-by date.
You'll also learn the best way to store miso in the fridge or freezer so it lasts a really long time and doesn't go to waste.
What is miso paste?
Miso is a typical Japanese fermented product (発酵食品 hakkō shokuhin).
Essentially, miso is fermented soybean paste.
It's made by fermenting soybeans, rice, wheat, and other grains with salt and a culture called koji (KOH-gee).
On par with soy sauce, miso is one of the key ingredients in Japanese home cooking. Many Japanese people grab their container of miso out of the fridge almost daily.
Because of its high salt content, miso lasts a long time if stored properly in the refrigerator or freezer.
Below, I'll go into detail about just how long miso will last in the fridge.
How long does miso last in the fridge after opening?
Generally speaking, miso has an expiration date of 3 to 12 months.
There are different types of miso pastes, such as soy miso (豆味噌), rice miso (米味噌) and barley miso(麦味噌). The expiration dates will vary depending on the type of miso.
I recommend that you check the expiration or best before date when you purchase miso.
The package of Hikari Miso I just bought at the end of October is labeled "best if used by" March. This does not mean my miso will expire in three months.
The label indicates that the taste and other qualities should remain consistent until this date. It will still be possible to safely consume the miso after three months, within reason.
Similar to pickles, miso is a "preservative food" (保存食 hozon-shoku).
According to Hikari Miso, "If kept in your refrigerator, miso itself does not go bad. In terms of the quality of the taste, miso should remain relatively consistent for up to one year."
But be aware that processed miso products, such as the dashi-filled(出汁入り味噌) and low-sodium miso (減塩味噌) products. These products have become common in Japanese grocery stores in recent years. They are more prone to spoilage than traditional miso.
How to store unopened miso
At the supermarket in Japan, you'll often find the miso on the shelf. It's not kept refrigerated.
Unopened miso paste can be stored at room temperature outside the fridge or in a dark, cool place away from direct sunlight.
The best place is where the humidity is low and the fluctuation of temperature is minimal.
Find a dry place, such as inside your kitchen cabinets, food pantry, or closet. Ideally, choose a storage space that doesn't get hit by direct sunlight from a window.
Does miso paste need to be refrigerated after opening?
Yes, miso is a perishable product.
Miso stored at room temperature after opening the package can change its flavor, and in some cases, mold may grow. It should be refrigerated or chilled immediately after opening the package.
When storing, seal tightly inside an airtight container to prevent exposure to air and store in the refrigerator.
In Japan, most people store miso in its original container. It's convenient and airtight.
How do you know when miso goes bad?
Miso that has been stored for a long time after opening or past the expiration date will change in color, smell, and flavor.
There are a couple of telltale signs of spoilage.
1. Darker Color, Dark Liquid, or White Mold
The first sign to recognize spoiled miso is its looks.
If dark liquid appears on the surface of miso, there is a possibility that mold has formed.
2. Sour Smell
When miso goes bad, it may develop a twangy smell in the back of your nose similar to paint thinner or alcohol or a strange odor like natto (fermented soybeans).
Take a good sniff! If miso doesn't pass the smell test, I don't bother tasting even a small amount. To me, this is already enough indication that I should toss it.
3. Sour Taste
When miso goes bad, its flavor also changes. It becomes more sour and astringent.
If the taste has changed from when you purchased it, it is evidence that it has gone bad and you should stop eating it.
To avoid food poisoning, do not eat miso that has a sour smell, sour taste, or mold growth.
Tip to Avoid Expired Miso
Unless you cook Japanese food for your family every week, I recommend buying the smaller size containers of miso.
If you can't find the smaller size at Asian grocery stores, you can find some options online.
How to store miso paste after opening the package
These are my storage tips to minimize miso's exposure to air:
Storing miso in its original plastic container
When miso is exposed to air, it oxidizes, turning darker brown. It loses its smell and flavor.
When putting miso in the fridge after opening the package, close the lid of the airtight storage container tightly.
You can also cover it with plastic wrap to prevent the miso from being exposed to the air.
It's a good idea to flatten any uneven surfaces of the miso and tightly seal the surface with plastic wrap before putting the lid on the storage container.
Storing miso in a bag
If you are storing miso in a bag directly in the fridge, lightly pound the entire bag on your kitchen counter a few times before putting it in the fridge. This will release the air in the space between the miso paste and the bag's opening, creating an airtight seal.
Seal the opening of the bag tightly with a rubber band before putting it in the refrigerator.
What is the key to making miso taste better for longer?
People think of miso as a preserved food with a long shelf life. But if stored improperly, miso can go rancid or change its flavor, making it unappetizing.
The key to making miso last longer is to be careful about temperature changes and the environment in which it is stored. It's important to store miso at low temperatures.
When storing miso in the fridge, make sure the surface of the miso is not exposed to air. Keep it at a low temperature to stabilize the miso and keep it tasting fresh for a long time.
Can you freeze miso paste?
Although miso can be stored at room temperature before opening the package, it is recommended that you keep it in the freezer if it will not be used for a while. This is especially the case during the summer months when the temperature is high.
The fermentation by yeast bacteria continues when stored at room temperature or refrigerated, the freezer has the effect of preserving quality. The activity of the yeast bacteria is suppressed by the cold temperature.
When freezing miso, the temperature of your freezer must stay higher than 25F or -5C.
Since miso contains many components other than water, including salt, it will not freeze or solidify at the temperature of a home freezer.
Can I eat expired miso paste?
Yes, if you've kept it in the freezer. An unopened container of frozen miso can be stored for 1 to 2 years. It can be eaten even after the expiration date listed on the container, as long as the flavor has not been lost.
When you remove the miso from the freezer, it should be refrigerated and used up within 2 to 3 months.
Miso that’s been in your refrigerator past its expiration date can often still be consumed safely. To avoid food poisoning, be sure to read the above sections on knowing when miso has gone bad.
When in doubt, throw it out. It’s not worth you getting sick.
Try these delicious miso recipes:
Once you try out some of these recipes, the leftover miso in your fridge will never go to waste again!
ABOUT THE AUTHOR
Asami Goto Miso Expert (Japan Safe Food Cooking Association (JSFCA))
Asami is currently developing miso recipes based on her knowledge, including its role in Japanese cuisine, how to select the right miso, the colors and flavors of various types of miso, and how to make miso at home. She is also conducting research on regional miso flavors, characteristics, history, and local miso cuisine to promote the appeal of traditional miso handed down in each region of Japan globally.