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I'm a fan of green tea and I find myself reusing the tea leaves 2-3 times a day. Sometimes I'll just store the leaves and reuse them the next day but it got me thinking if what I'm doing is actually "safe", I know that the taste isn't the same.

So my questions are:

  • What's the best way of storing tea for reuse? Currently I drain the leaves and put them in a small sealed glass jar.
  • Is it safe to store tea to reuse the next day? Bonus point for an actual reference/research proving that it has bad or no side effects whatsoever.
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I generally leave mine in the mesh container inside my (emptied) teapot, but I brew a small pot and then pour into a travel mug. Depending on the tea, we've gotten as much as three or four pots out of one batch of leaves. I have no idea if this is safe, but I do it regularly. I'd be interested to see any actual studies. –  Yamikuronue Jun 25 '12 at 12:28
    
I would rather (and do) just use new leaves after each cup or two. –  Kim Nov 14 '13 at 6:41
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6 Answers

up vote 7 down vote accepted

Here in China, it is normal to reuse tea again and again. Typically the first cup from the tea is bitter. Chinese people commonly pour one cup and then throw it away and drink the second cup from the same leaves. Workers here can be seen with a large mug or jar of tea. When drunk, they top up the water again with hot (but not boiling) water. This will go on all day.

The next day, however, they will not reuse the tea. My Chinese wife always tells me off if I reuse the previous days tea leaves. She says they are bad for you, though I have never had any problem myself.

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that's what I heard too but I haven't found anything saying why they're actually bad for you –  Serge Oct 14 '11 at 22:25
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I don't think Chinese medical advice needs any references. It's bad for you because your Grandmonther's Grandmother's Great Grandmother, going back 5000 years, said so. And you can argue with her. –  Rincewind42 Oct 15 '11 at 14:50
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As I understand it, the wet leaves are prone to fostering pathogens, so you should discard it because of food safety reasons, not potency reasons –  Ray Oct 21 '11 at 2:36
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I made this comment on a similar question: Doesn't pouring off the first cup get rid of most of the caffeine? I've read that if you want to reduce caffeine that's the way to do it. Not that green tea has much caffeine, but some of us like the small boost of it. –  Marplesoft Oct 27 '11 at 17:52
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I actually found a source that says you should store them in a MOIST medium in the refrigerator to inhibit the growth of pathogens. apartmenttherapy.com/reusing-tea-bags-the-good-the-128466 –  scientifics Jun 25 '12 at 14:55
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The question of how safe it is to store wet tea leaves is related to the question of how safe it is to store iced tea; after all, drained or not, the used tea leaves are still bathed in cold liquid tea.* That being the case:

CDC - Memo on Bacterial Contamination of Iced Tea (1996) (following quotes come from link)

Regular tea is hot brewed, and "studies conducted at T.J. Lipton showed that iced tea brewed at 175°F or higher and stored at room temperature had no detecteble coliform counts during the first 16 hours of storage." So the issue is "primarily one of storage conditions of the tea" (or in this case, wet leaves). CDC claims the "theoretical risk of disease transmission would be minimized if tea is brewed hot, and stored in clean urn and stored for no longer than 8 hours." Also, regularly clean and sanitize your equipment.

An eight hour limit seems too stringent me, but they are trying to eliminate a theoretical risk. Real world risks are often less persnickety.

See also Iced Tea Safety (2010) for a slightly less techy version of the information.

*and the liquid tea always contains bits of tea leaves.

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I'm Canadian Chinese; my parents have always reused tea leaves. Supposedly it's fine to reuse tea in the same day. However, my Chinese co-workers told me it becomes poisonous to reuse tea longer than that.

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I don't know about "poisonous", but certainly something that's been soaked in hot water then left out at room temperature for longer than several hours is not a good thing food-safety wise. –  Jefromi Jul 31 '12 at 22:01
    
Without refrigeration, it could be dangerous. All it takes is one mold spore to land on the moist leaves and they've got a great playground. If you refrigerate immediately after finishing, that really shouldn't be an issue (even if spores happen to hit them, the cold temperature should retard any growth). Beyond that, almost no spores will survive near boiling water. –  Matthew Jan 11 '13 at 1:44
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I reuse the leaves the next day as well. As far as the food safety issues go, keep in mind that you are submerging the leaves in boiling water. Contrary to popular belief it doesn't take 15 minutes to purify water. As far as I know brewing the tea would be sufficient kill anything dangerous, forgetting for a moment how unlikely it is that some sort of pathogen would develop in the first place.

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According to Golden Moon Teas, the composition of wet tea leaves encourages bacterial growth, and they don't recommend reusing used leaves after three hours.

That said, they also suggest that drying out the tea leaves will dramatically increase their remaining life. They suggest removing as much moisture as possible, and then spreading the leaves out on a platter in a well ventilated room to dry. My intuition tells me that this process could be slightly improved by using a clean towel to press them, and then placing a different towel below them while drying.

Regardless of method, the recommendation is that re-dried tea should be used the next day, and that any delay furthers the chances of dangerous bacterial growth. I would expect that the drying process itself, however, can also encourage said bacterial growth. Using an oven, a dehydrator or just having a fan blowing on the leaves would reduce the drying time, which would therefore reduce the risk of growth.

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While I appreciate your answer, the 3 hour rule just can't have any truth to it. If it would be unsafe to drink, all these tea drinking Chinese people Rincewind42 is talking about, user15144 and myself would have gotten sick a lot of times. I've been reusing tea leaves for at least up to 10 hours (without steeping during this time), stored in room temperature in a ceramic tea infuser. I can see the rule apply to areas where you have very bad water though, but not in most developed countries. –  citizen Jan 10 '13 at 23:36
    
I'd certainly agree that 3 hours is very conservative, but current food safety practices usually aim for very conservative risk levels. As a result, I doubt there is research or official documentation covering the extended reuse of tea leaves. For the sake of argument, tea reuse after 10 hours could still entail relatively low risk, but there's almost certainly not enough interest in such reuse to justify any meaningful research to back that up. Also, there's the question of if "low risk" means a 1 in 10 or 1 in 1000 chance. This could be a situation where the only choice is amateur research. –  OmniaFaciat Jan 11 '13 at 2:39
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If you are making hot tea, you shouldn't have an issue. Remember, to pasteurize you only have to raise core temperatures up to 155 degrees fahrenheit and hold for a few minutes (a few seconds in the case of flash pasteurization). Assuming you are going to steep your tea in water just under boiling (or you are going to just let the tea leaves sit in the beverage) you should far exceed the amount of time required to thoroughly kill any nasties.

At that point the only concern is that, if nasties have a chance to start growing between uses, they could produce chemicals which are dangerous. This is common with some molds and fungi. If you put your used leaves in the refrigerator after use and keep them there, this shouldn't be an issue at all (the cool temperatures will either kill or highly retard the ability of the bacteria to go about their metabolic business). I wouldn't go using the same leaves every day for a week, but I can't think of a legitimate reason that an item that is being darn near sterilized every time it is being used, or at the very least pasteurized, would be dangerous.

Now, taste is another story. That may get nasty. But hey, one person's nasty flavor is the next person's gourmet so give it a shot.

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When pasteurizing you choose temperature and time depending on what pathogens you want to kill, so to categorically say that you only need 155˚F/69˚C for a few minutes is not correct. You will need to know which microorganism are prone to grow in the tea leaves you are using and how to kill them, before choosing time and temperature. And, as you mention, killing spores and killing toxins can require (very) different temperatures. Some pathogens need well above 212˚F/100˚C to be inactivated. –  citizen Jan 11 '13 at 2:36
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