Pantry and shelf-stable reference

Does miso need to be refrigerated after opening?

Yes. Hikari Miso's instruction is plain: once the package is opened it should be refrigerated, and the date on the tub marks peak flavour rather than expiry.

Unopened and opened

A shelf-stable package has two different lives, and only one of them is printed on the label. These are the windows How to Store Miso Paste, Hikari Miso publishes, in its own units. Where it publishes none, this page says so rather than filling the gap.

Unopened: How to Store Miso Paste, Hikari Miso gives no unopened window for miso; go by the best-by date on the package.
After opening: How to Store Miso Paste, Hikari Miso gives no after-opening window for miso, only the storage instruction above.
Where to keep it once open: Refrigerator. Refrigeration is required here, not optional.

How to use this window

The after-opening window runs from the day the package was opened, not from the date printed on it, so that date is only useful if you wrote it down. Well Stockd does not know when this package was made, bought or opened: record the opened date, follow the package directions, keep your refrigerator at 40°F or below, and use the official item listing when food safety is in question.

Primary sources and limits

The windows above are quoted from How to Store Miso Paste, Hikari Miso. Storage times are guidelines: quality varies with packaging, temperature, and how the jar is handled between uses. Nothing here overrides a package instruction that says to refrigerate.