Why you might want to add salt to your tea

In Steeped, professor Michelle Francl explores the chemistry of the world’s most popular beverage

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For Bryn Mawr College chemistry professor Michelle Francl, the best cup of tea made with science involves ping pong balls and a sous vide machine. Agitating loose-leaf black Assam tea for four minutes in a 93.5 degrees Celsius constant temperature bath may be too fussy for the day-to-day. (“I just want my tea in the morning.”) But it produces a perfectly balanced cup: astringent and bitter, rounded out with some sugar.

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Francl drank at least 483 cups of tea while writing her new book, Steeped: The Chemistry of Tea, and read more than 500 papers while researching it. “One of the things I learned from doing this research is that temperature is so important, and keeping the temperature high (is important),” she says. Even if you pre-warm your mug or teapot, which she now does religiously, the temperature drops. And because she’s wired her teapots with sensors, Francl knows exactly how cool the tea gets and how quickly.

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“I sous vide stuff all the time. And I thought, maybe I could do the same thing I would do in the laboratory and use a constant temperature bath. So, I rigged up the sous vide and put the tea in, and, for me, it’s the perfect cup of tea.”

As enjoyable as this lab-inspired cup is, most often, Francl uses an electric kettle, pre-warming either a mug or teapot while waiting and pouring the water as soon as it comes to a boil. “It drives my husband nuts. If it’s been a minute, I bring it back to the boil. He’s like, ‘You know it’s still hot.’ I’m like, ‘But not hot enough.’ Now I have all the research to prove it.”

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Of the many chemistry-backed tips for a better brew Francl features in Steeped, one seemingly innocuous piece of advice caused an international incident, raising eyebrows among British tea lovers and eliciting a viral tweet from the U.S. Embassy in London.

As anyone who has enjoyed dark chocolate studded with sea salt or a miso chocolate chip cookie can attest, pairing salt with bitter foods often has delicious results. But to some, adding a pinch of salt to tea to cut the bitterness was a step too far. “I didn’t expect it to be the one that would set the British Isles afire,” says Francl.

Adding salt to tea is a long-established practice dating back to the Tang dynasty in China. You can experience it today in drinks such as Mongolian suutei tsai and Tibetan butter tea.

In his book Classic of Tea, Lu Yu suggests adding a pinch of salt to the water before infusing the tea leaves to reduce the bitterness. Bridging Lu Yu’s 8th-century treatise and the 21st-century chemistry literature was challenging, says Francl, since sodium and salt are ubiquitous terms. (She found what she was looking for in the coffee literature “because it’s the coffee people who really figured it out.”)

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Steeped: The Chemistry of Tea book cover
In Steeped, professor Michelle Francl explores the chemistry of the world’s most popular beverage. Photo by Royal Society of Chemistry

As a fan of tea’s inherent bitterness, Francl doesn’t regularly add salt to her cup. Instead, she considers it a rescue technique — a hack for when she’s over-steeped her tea on the way out the door and could use the caffeine. Just a pinch makes it palatable. The metal ions in salt reduce the perception of bitterness, similar to adding sweeteners or milk. The key is to add just enough salt — not so much that you taste it.

(I tried it with over-steeped Darjeeling tea; both cups were at the same temperature and concentration, one with salt, one without. The salted cup was noticeably less bitter without tasting salty. Interestingly, the astringency was just as intense.)

Armed with an understanding of the science, Francl hopes readers will experiment to figure out how to make their perfect cup of tea. Dunk the teabag and squeeze out the remaining tea if you want more antioxidants. If you’re after a little less bitterness, try adding salt.

The tea sommeliers I spoke with about the uproar agreed: The “proper” way to make tea depends on the drinker. “Adding a pinch of salt is down to personal preference. To me, there’s no right or wrong way to brew tea. Whatever works for you is the best,” says tea sommelier and Chinese tea master Claudia Tse, co-founder of Teakan Tea Co. in Vancouver.

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Tea may be Britain’s national drink, but it’s also the world’s most popular beverage. Who’s to say what people can or cannot do in their mug? “The British do not own the culture of tea,” says Toronto-based tea sommelier and writer Linda Gaylard. “They have no problem adding tons of milk and lots and lots of sugar to their tea. But they would react to the idea of putting a pinch of salt, not so much to improve the flavour, but to improve our sensation of the flavour on our tongue.”

Tea is a bitter beverage by definition, adds Gaylard, and you can play around with that bitterness to suit your palate. She suggests experimenting with 30-second increments when brewing (instead of setting a timer for three minutes, for example), using a small vessel to control the infusion, tasting after each increment and noting the details of cups you enjoy.

Tse appreciates the gong fu, or “brewing tea with skill” method, which uses a high ratio of tea leaves to water and short infusions (10 to 30 seconds). She says this method produces a more delicate aroma, though some bitterness is still central to the experience. In Chinese culture, many enjoy “return sweetness” (hui gan) after consuming something bitter, whether tea or bitter melon. “Some people like to brew their tea really, really strong so that it hits your face with this bitterness, and then the complexity will develop, and then you have all the sweetness, all the floralness. It’s quite an interesting sensation.”

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The bottom line, says Gaylard, is to enjoy tea as you like it: “Just be mindful when you make it. Try to make the best cup you can. Respect the cup, respect the leaf and enjoy your tea.”

Francl wrote Steeped for “tea-drinkers who may or may not be chemists.” The most fun part of the unexpected controversy has been seeing people engage with science. “I love that a radio host in South Africa told me about the experiment he did with three cups of tea, all brewed at the same temperature. It was really fun to see people trying to channel their inner scientist.”

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