Storing After Opening (開封後の保存)
One page for the fridge door: how each family in this guide keeps once opened, and what changes are normal.
| Miso | Refrigerate after opening. Smooth the surface flat; colour will deepen over weeks - normal |
|---|---|
| Shoyu | Cap tightly; refrigerate to keep aroma (the maker's label governs). Use opened bottles within the maker's stated period |
| Shio koji / shoyu koji | Refrigerate after opening, clean spoon each time |
| Pickles, commercial packs | Refrigerate after opening and eat soon - days for asazuke-style packs, longer for salt-heavy traditional types; the pack's date rules |
| Dried koji | Seal against moisture; cool and dark, or refrigerate for long keeping |
The pattern behind the table: salt and acidity preserve these foods, oxygen and warmth undo their aroma. Almost every 'went wrong' story is an opened bottle kept warm for months - the ferment had finished its work, and oxidation did the rest.
Freezing works for miso (it stays scoopable, being too salty to freeze solid) and for natto (its standard export form). It does not suit shoyu in glass or fresh pickles, whose texture is the point.
See also
Storage and best-before datesRelated page in this guide.Reading a miso label
Related page in this guide.
Sources: Ministry of Agriculture, Forestry and Fisheries (MAFF), 'Traditional Foods in Japan'; JAS soy sauce standards; Umami Information Center; Kikkoman official information; Wikipedia (CC BY-SA 4.0). Checked 6 November 2026.