What are the common misunderstandings about keeping barley tea and other cold-brewed drinks safe?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
A jug of cold tea in the fridge is part of every Japanese summer. Barley tea (mugicha) is the classic, and as cold brewing spreads abroad, "how long does it keep?" is asked more and more often. The answer surprises many people: mugicha spoils faster than you would expect.
What to look for
| Drink | Guide (refrigerated) | Why |
|---|---|---|
| Mugicha (cold-brewed or boiled) | 1–2 days | Contains starch and sugars that feed bacteria |
| Green tea (cold-brewed) | 1 day | Catechins are antibacterial, but it must not be left at room temperature |
| Black tea, rooibos (cold-brewed) | 1–2 days | As above |
| Tap water (stored) | 2–3 days refrigerated (deteriorates once the chlorine is gone) | Tokyo Metropolitan Waterworks Bureau guidance |
- A Tokyo Metropolitan Government study reported that mugicha left at room temperature showed a large increase in bacterial counts within a few hours.
- The Tokyo Metropolitan Waterworks Bureau gives 2–3 days refrigerated for stored tap water, and the same day at room temperature (the chlorine dissipates and the disinfecting effect is lost).
- The spout and gasket (パッキン, pakkin) of a bottle or jug are where grime lingers most.
[Verify] Check the figures from the Tokyo mugicha study in the published material of the Tokyo Metropolitan Institute of Public Health, and the stored-water guide in the Tokyo Metropolitan Waterworks Bureau Q&A.
Misunderstanding 1｜Boiling sterilises it, so it keeps longer
Just after boiling the bacterial count is low, but bacteria get in as it cools and every time you pour. Boiled mugicha is also 1–2 days in the fridge. Let it cool down first, rather than putting it in the fridge hot.
Misunderstanding 2｜Leaving the tea bag in makes it stronger
Left in, it produces off-flavours and cloudiness, and gives bacteria a foothold. Take the bag out once the brewing time is up.
Misunderstanding 3｜Rinsing the jug with water is enough
The starch in mugicha stays on the inside as a slimy film. Wash it every time with detergent and a sponge, taking off the lid, gasket and spout, then dry it. For narrow-necked bottles, a long-handled sponge is the standard tool.
Misunderstanding 4｜Drinking from the bottle is fine as long as it goes back in the fridge
Once you drink from the bottle, bacteria from your mouth get in, and if there is sugar they multiply fast. Anything you have drunk from should be finished the same day; better still, pour it into a glass.
Misunderstanding 5｜The cloudiness or sour taste is my imagination
Cloudiness, sourness, thickening or a change in smell are signs of spoilage. If in doubt, throw it out — that is the safe side.
---
Sources
- Tokyo Metropolitan Institute of Public Health, "Study on bacterial growth in barley tea" [麦茶の細菌増殖に関する調査]
https://www.tmiph.metro.tokyo.lg.jp/
- Tokyo Metropolitan Waterworks Bureau, "Precautions when storing tap water" [水道水をくみ置きする場合の注意]
https://www.waterworks.metro.tokyo.lg.jp/kurashi/shitsu/
- Ministry of Health, Labour and Welfare (MHLW), "Six Points for Preventing Food Poisoning at Home" [家庭でできる食中毒予防の6つのポイント]
https://www.mhlw.go.jp/www1/houdou/0903/h0331-1.html
⚠️ 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.
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