For the Perfect Cup of Tea, Add Salt, Says Chemist

Ask tea drinkers how to make the perfect cup and you're sure to get all kinds of responses. Use loose leaf. Steep extra long. Add milk last. Don't add milk at all. The best tea, after all, is subjective. Or is it? Michelle Francl, a professor of chemistry at Bryn Mawr College, thinks she's come up with the best recipe based on research papers, ancient texts, and her own experiments. And as the Guardian reports, it's somewhat controversial. Francl suggests adding a pinch of salt—not sugar—as the sodium ion blocks the chemical reaction that makes tea taste bitter. But that's only part of the perfect recipe Francl explores in her new book, Steeped: The Chemistry of Tea, out Wednesday.

For best results, use loose leaf tea. "You get more caffeine and more antioxidants" that way, Francl explained in a 2020 essay published in Nature Chemistry. If you do use tea bags, they should be fairly large to allow the leaves inside to move around, getting plenty of contact with the water, she tells the Guardian. "Tea leaves expand by maybe a factor of four or five, and if you don't give them enough space, there's not enough good access from the solvent," Francl says. She recommends a quick steep while squeezing the bag to reduce the amount of bitter-tasting tannins. With decaffeinated tea, Francl recommends a 30-second steep, after which the liquid is removed, followed by a five-minute steep with fresh water.

The vessel is important, too. Short, stout mugs with less surface area help keep the liquid hot, allowing for the release of more "beautiful aromatic compounds," Francl tells the Philadelphia Inquirer. "If you can, you want to warm up your cup by running a little hot water in it." And whatever you do, don't boil your water quickly in the microwave. "You don't get rid of the oxygen, and that helps precipitate this reaction with magnesium ions and carbonates, essentially the same stuff that makes bathtub scum," resulting in a "funny white film on the top of your tea," Francl says. A splash of lemon juice can remove this scum, per the Guardian. As for milk, it should be warmed and added after the tea is poured to reduce the chance of curdling. (More tea stories.)