Is it safe to reuse loose tea leaves the next day? What precautions need to be taken for storing tea for reuse?

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.

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.

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.

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.

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.

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.

In my experience, it can last for up to 24 hours, but it must be stored correctly. I hope this infographic helps.