If you’ve ever used a tea bag, chances are that you’ve squeezed the last bit of liquid out of it and into your cup after the tea has finished steeping – and possibly burned your fingertips doing it if you don’t have some ind of tea bag strainer. You might also have heard that squeezing a tea bag, once brewed, into a cup of tea will turn the tea bitter and that you should never, under any circumstances, do this.
If you put this to the test, you’ll probably find that it’s true, to some extent. Tea, especially black tea, contains tannins, a plant polyphenol that is known to have a bitter, astringent taste to it. It is not the same as tannic acid, a chemical present in different types of wood (such as oak) that is, among other things, used to tan leather. This astringency is more noticeable when your tea is stronger, and often squeezing the bag after steeping will release an extra little burst of well-steeped liquid from within the tea bag – and this can add a slight bitterness to the tea. That being said, if you are steeping your tea for a reasonable amount of time, you’re not going to notice a huge change.
It’s worth noting that herbal teas, as well as white and green teas, contain little to no tannins depending on the makeup of each individual tea. Those tea bags can be squeezed to your hearts content without any worry about adding unwanted bitterness to an otherwise good cuppa.