A question came up the other day on our Facebook page: “If over steeping a tea can make the cup bitter, then why is the same not evidently also true for multiple steepings? Won’t the additional steepings be more bitter than the previous ones?” At the time, we gave a short and not very well thought out response but now want to take the time to post a longer and better response here. The question was a good one and really got the gears in our brain to creaking. Please bear in mind that we are not chemists and are presenting the information in as clear a way as possible for those of you who are also not chemists. Hopefully, the chemists out there will chime in wherever we go astray here.
The basic questions seems to be why a long infusion of a portion of tea leaves would yield one result and several short infusions of a portion of tea leaves would yield another. At least, that’s how we’re reading it here. Let’s take these one at a time.
Why a Long Infusion Turns Bitter
Let’s start by saying why tea is bitter in the first place and go from there. In a word, tannins. Camellia sinensis, the species of plants from which teas (not the herbal kind) are made. It has a naturally high tannin content. Tannins are released into the water during the infusion process. This is good due to the catechins and other flavonoids in the tannins. But too much can cause the tea flavor to turn overly tart or astringent.
A big mistake often made when infusing tea leaves is using too few leaves and infusing a longer time to get a stronger flavor, thus releasing too much of the tannins. Another mistake is using poor quality tea leaves or leaves from a cultivar that tends to be bitter (the assamica varietal comes to mind here, but the ones grown in India tend to be more bitter than those grown in Yunnan, Kenya, and elsewhere). Of course, the processing of those leaves can make a big difference in how they infuse. The Yunnan leaves are processed into máochá and then stored to ferment or they undergo wo dui (wet pile fermenting). The longer they are stored, the less likely they are to have any bitterness in the infusion. Some say 15 years is a minimum time.
Water quality can also contribute to bitterness, especially when infusing a tea for several minutes. Minerals and other elements in the water can make it “hard” and influence the tea flavor. Too few of these, though, makes the water “soft” and gives you a “flat” tasting tea. The right amount is needed. Plus, avoiding water that has chlorine or chloramine in it also helps.
All of these are factors that explain bitterness. But why a long infusion is more likely to be bitter than a number of shorter infusions is another matter. The longer you infuse the leaves, the more tannins are released from the leaves and go into the water. Too few will rob you of the benefits of drinking tea and/or give you a weak tea flavor. Too much will cause that bitterness. The longer you infuse, the more tannins are concentrated in the tea liquid.
Why Multiple Short Infusions Aren’t as Likely to Turn Bitter
A great thing about using a gaiwan or Yixing pot for infusing tea leaves is it encourages shorter infusion times. Just be sure to use a sufficient amount of tea leaves to get a good flavor from those short infusions (often less than a minute in duration). The main appeal of these shorter infusions is their tendency not to let tannins build up an overly intense concentration in the water. You may eventually experience some bitterness and can then decide whether to continue infusing the leaves or stop. Unlike one long infusion, therefore, you can get a number of good infusions before reaching that bitter stage.
The key is concentration of tannins in the liquid. Shorter infusions don’t build up that concentration. Longer infusions do. And now you know.