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.
It's hard to know exactly what you're referring to without any context of the event, location, or what you remember it tasting like, so I'll give you my best educated guesses.
- If your pink tea sweet and fruity or floral, it was an herbal tea - tisane, and not true tea. ("Tea" actually refers to the plant whose leaves are used the beverage. Anything that is not made from the tea tree is usually called a tisane.) Some varieties of tisanes that produce a pink liquid include hibiscus, rose petals, rose hips, strawberry.
- If the above is not the case, I suspect you're referring to Kashmiri pink tea, sometimes called noon chai.
Disclaimer: I can't find any authoritative sources about Kashmiri online; my knowledge of the subject is anecdotal from my own travels in India as well as stories from people I know who have lived or traveled in South Asia. My understanding is that, like masala chai throughout South Asia, pink tea has some general guidelines but everyone customizes it according to taste or local custom.
The basic distinguishing factors of Kashmiri pink tea compared to a "regular" black, green, oolong, or white tea are twofold: color and taste. As you mentioned, this tea is pink in color, which other beverages made from the tea tree are not. The pink color comes from the addition of baking soda. As for taste, pink tea tends to elicit mixed opinions about taste because it is salty; most people around the world typically drink tea unadulterated, or sweetened, but rarely with the addition of salt.
Pink tea shares many ingredients with masala chai, often including some or all of the following:
- Ginger
- Cardamom
- Cinnamon
- Peppercorns
- Milk or cream
- Sugar (or other sweetener)
Unlike masala chai, which is normally prepared with black tea, Kashmiri pink tea uses green or oolong tea leaves.
Ingredients included in Kashmiri chai that are not included in most other chai recipes:
- baking soda (just a pinch)
- ground pistachios and/or almonds
- salt
- white poppy seeds
The final major difference is in the method of preparation. Masala chai can be made in a matter of minutes by boiling the water, then adding tea, milk, spices and boiling it all together for a few minutes before straining and serving. Kashmiri chai, on the other hand, takes 1-2 hours to prepare (I believe the long boiling time is required for the baking soda to accomplish its task of turning the tea pink). I don't know the exact process and couldn't find any sources that seemed reliable.
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The descriptions of grape leaf tea I have seen don't mention a specific age to pick the leaves at - so leaves of most any age are likely to be fine, it probably isn't necessary to only pick those of a certain age, say, the newest leaves or anything. Grape leaves are also edible (stuffed grape leaves, or pickled ones) so you may not need to worry about toxicity, either. However, some sites do mention medicinal value, which means you should be careful about dosages until you're sure about the effects drinking the tea will have on you.
In general, I would expect the tea to be made from mature, medium-sized leaves, since that's the type picked for cooking with (and so most likely to be on hand when someone goes, "what if we made it into tea?"). Older leaves may have less flavor, since that (along with texture) is one of the reasons they're not preferred for cooking with. New leaves might not have enough flavor to be apparent, or might take more effort to get enough of them to make a difference, or smaller size per leaf means an equivalent volume might have an adverse effect on the vines.
Grape leaves are usually harvested late spring to early summer, though if you look at sites dedicated to the harvesting of grape leaves for other culinary purposes, you may find more specific information including harvesting dates or locations for your particular area. The type of grape vine (green, red, wild) may also make a difference to your tea and its effects, though all of them should be nontoxic.