Value Village ／ Food & living
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Potatoes and onions are staples of the Japanese kitchen, but the same failures come up again and again: "it had sprouted before I noticed", "it had turned green", "the onion had gone soft from the inside". The sprouts and green parts of a potato contain a natural toxin, and mass food poisoning has occurred in Japanese school gardens. Here we sort out where to store each vegetable and where the line between "edible" and "throw it away" lies.
| Vegetable | Where | Rough keeping time | Notes |
|---|---|---|---|
| Potatoes | Dark, cool place (around 10°C), in a paper bag or cardboard box to keep out light. In summer, wrap in newspaper and use the fridge's vegetable drawer | Room temperature (spring, autumn) 1–2 months; fridge vegetable drawer 2–3 weeks | Light turns them green and raises solanine levels. One apple in the box slows sprouting (ethylene) |
| Onions | Room temperature with good airflow. Hang them in a net or an old pair of tights, or lay them out so they do not touch | 1–2 months | Moisture makes them rot. Never leave them in the plastic bag. Wrap cut onion in cling film and refrigerate, 3–4 days |
| New-season onions (shin-tamanegi) | Fridge vegetable drawer, wrapped in newspaper | 1 week | High in water; spoil within days at room temperature |
| Sweet potatoes | 13–15°C, room temperature. Refrigeration causes chilling injury | 1 month | Sensitive to cold |
[Verify] Check the number of solanine-poisoning cases and the symptoms against MAFF and Ministry of Health, Labour and Welfare (MHLW) materials, and the acrylamide explanation against the relevant MAFF page.
The green skin also contains a lot of toxin and needs to be peeled thickly. The safe choice is to discard potatoes that are green all over, taste bitter, or are small and immature.
Solanine-type toxins break down very little with heat. Removing them is the only countermeasure.
Cold increases the sugars, so fried and stir-fried potatoes burn more and produce more acrylamide. In spring and autumn, a dark place at room temperature; only in summer, the vegetable drawer, wrapped in newspaper.
The moisture inside a plastic bag makes them rot. Take them out and hang them in a net or lay them in a basket. One rotten onion spreads to its neighbours.
The moisture from the onions makes the potatoes spoil faster, and sprouting or rot on the potatoes spreads to the onions. Keep them in separate containers.
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https://www.maff.go.jp/j/syouan/seisaku/foodpoisoning/naturaltoxin/potato.html
https://www.maff.go.jp/j/syouan/seisaku/acryl_amide/
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/shokuhin/syokuchu/poison/
⚠️ 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.
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.
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