An unopened can of miso will not likely expire because the fermentation process will keep going.
However, at some point, the quality may gradually degrade. An opened miso may also unlikely expire if stored properly.
The more often you open the jar, the more prone it is for contamination and quality degradation. Eventually, you might need to throw it away.
How Long Can Miso Last
Miso can last long because it will keep on fermenting as long as the package is still sealed.
It does not even need chemical preservatives. Once you open it, miso will start degrading its quality and taste.
An unopened jar of miso can last about a year before starting to degrade. Most companies may put the “best before” label on the package to notify the estimated time when the miso would likely start degrading.
However, most of the time, miso would still be safe to consume even a few months after the date.
An opened miso is quicker to degrade, especially if the jar is opened too often or not properly sealed.
There is a chance the miso will get bacteria contamination that makes it get mold or smells bad.
In general, you only have three months to keep the miso once you open the package.
How to Store Miso
If you haven’t opened the miso jar, it can stay in a cold room temperature.
So, a kitchen cabinet is still fine. Avoid placing it near the stove or oven because heat will heavily affect its quality.
After you open the jar, the miso will start degrading. Move it into the fridge to slow down the process.
Make sure to close it well because even a little bit of air will affect the miso. Use a clean and dry spoon every time you scoop out the miso paste to avoid contamination.
How Miso Turns Bad
Once opened, miso will gradually lower its quality in terms of taste and smell. It is still normal and safe as long as there are no subtle differences in it.
However, if your miso has developed discoloration, it is best to throw it away.
When reopening your miso jar, see if it looks different than it should look. You can give it a little sniff to make sure it still smells fine before you use it for cooking.
If you are still unsure, you can scoop a tiny bit of it and try tasting it.
Miso has a low chance of expiring. But that doesn’t mean you can be reckless about it.
If you are not sure you can finish the miso in three months after opening it, you might better buy the smaller package. But while you have it, be sure to store it properly.
This is my favorite miso brand:
Japanese Miso Paste:
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Also, you can check out these miso substitutes if you don’t have it (or just had to throw it away after reading this).