What are the common misunderstandings about storing yoghurt and using it after opening?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Yoghurt is the classic example of a food people assume "is fermented, so the date does not matter." Japanese supermarkets sell it mostly in large 400 g tubs, which raises the question of how long it lasts once opened. Here is how to handle an opened tub, what the liquid on top is, and how to judge a passed date, based on how Japanese labelling works.
What to judge by
| Item | Details |
|---|---|
| Storage | Refrigerate (10°C or below). Avoid the door pocket, where the temperature rises easily |
| Best-before date while sealed | Usually 2–3 weeks from manufacture. If unopened and refrigerated, it is often still fine a few days past the date (check its condition) |
| Once opened (large 400 g tubs etc.) | 2–3 days. Serve with a clean spoon; do not eat straight from the tub |
| Liquid on the surface | Whey (乳清). Contains protein and calcium. Stir it back in |
| Signs to throw it away | Too sour, bitter, pink/black/green spots (mould), a bulging lid, a smell of alcohol |
| Freezing | Possible, but the texture changes (it separates). Eating it as frozen yoghurt is one option |
- Most yoghurt is labelled "fermented milk" (発酵乳, hakkō-nyū), defined in Japan's Ministerial Ordinance on Milk and Milk Products as non-fat milk solids of 8.0% or more and 10 million or more lactic acid bacteria per 1 mL.
- Claims such as "reaches the gut alive" are allowed only on products approved or notified as Foods with Function Claims or Foods for Specified Health Uses (FOSHU, トクホ), two Japanese regulated categories; ordinary yoghurt cannot carry them (Health Promotion Act; Act against Unjustifiable Premiums and Misleading Representations).
- A best-before date (賞味期限, shōmi kigen) is the limit for eating the food at its best; it differs from a use-by date (消費期限) (see the article on date labelling).
[Verify] The standard for fermented milk is in the Ministerial Ordinance on Milk and Milk Products Concerning Compositional Standards; check the after-opening guideline against makers' labels and Q&A pages.
Misunderstanding 1｜The liquid on top means it has gone off
It is whey. Pouring it away loses nutrients. Stir it in or eat it as it is. Cloudy liquid with a strong sour smell is a different matter.
Misunderstanding 2｜One day past the best-before date, throw it away
If unopened and refrigerated, it is often still fine a few days past the date. Judge by appearance, smell and taste. Once opened, 2–3 days regardless of the date.
Misunderstanding 3｜Eat from the tub with a spoon and put the rest back in the fridge
Bacteria from a spoon that has touched your mouth get in and speed up spoilage. Serve a portion first.
Misunderstanding 4｜It is fine to say that eating yoghurt sorts out your gut
Specific effects may only be stated on products that have been approved or notified. Within the law, ordinary yoghurt is positioned as "one of the fermented foods".
Misunderstanding 5｜All yoghurts contain the same bacteria
The strains differ from product to product (Lactobacillus bulgaricus, Streptococcus thermophilus, bifidobacteria, Lactobacillus gasseri, etc.). Which suits you varies from person to person; the practical approach is to choose one you can keep eating.
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Sources
- Ministry of Health, Labour and Welfare, "Ministerial Ordinance on Milk and Milk Products Concerning Compositional Standards" [乳及び乳製品の成分規格等に関する省令（乳等省令）]
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/shokuhin/
- Consumer Affairs Agency, "Foods with Function Claims" and "Foods for Specified Health Uses" [機能性表示食品について／特定保健用食品について]
https://www.caa.go.jp/policies/policy/food_labeling/foods_with_function_claims/
- Consumer Affairs Agency, "Date labelling of foods" [食品の期限表示について]
https://www.caa.go.jp/policies/policy/food_labeling/food_sanitation/expiration_date/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
Some ingredients need thorough cooking. Eat raw only foods that are sold for raw consumption. If you have allergies, check the ingredients.
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