How to make the perfect cup of tea: Read a scientist’s five-step plan that was three years in the making for the ultimate cuppa (which includes a few surprises)

Michelle Francl never expected her book to cause such a stir. The 65-year-old chemistry professor at Bryn Mawr College in Pennsylvania had written a scientific exploration of tea entitled Infused: The Chemistry of Tea.

It ran to about 200 pages and was published by the Royal Society of Chemistry at the end of January.

‘I got up in the morning. I had a nice note from my editor congratulating me on the book launch. When I arrived at my office, there was a note from my publisher’s press group saying, “Would you like to respond to the U.S. Embassy’s statement?” I thought, “What statement from the American embassy?”

A little context. In Francl’s book, in a small paragraph on page 168, she suggests that drinkers should add a dash of salt to save over-brewed tea. Somehow the internet found out about this and by the morning of publication, Francl’s advice had gone somewhat viral.

The US Embassy issued a funny press release on Twitter, saying: ‘Today’s media reports about an American professor’s recipe for the ‘perfect’ cup of tea have put our special bond with the United Kingdom in hot water… We want to assure (sic) the good people of Great Britain that the unthinkable idea of ​​adding salt to Great Britain’s national drink is not an official policy of the United States. And that will never be the case.’ The post received 74,000 likes.

“It was funny and a bit overwhelming,” says Francl, smiling, as she sits in her office with a large mug of (unsalted) tea.

‘I really didn’t recommend adding salt as part of the general tea brewing process. It’s more of a rescue operation. And boy, I saw people on TikToks putting in a teaspoon of salt. Of course that’s going to taste terrible!’ Still, all press is good press, and after Francl and I disconnect from Zoom, I purposely make too much tea and carefully add a pinch of salt. To be honest, I can’t really taste it. (And the tea actually seems fine.)

Francl’s book was the result of three years of research. She read more than 500 scientific articles about tea; she fitted her mugs with thermometers to calculate the rate at which certain concoctions lost heat; She used a method using silicone balls – typically used to determine the volumes of meteorites – to determine the capacity of tea eggs.

She drank a lot of tea. According to Francl, the perfect cup is made as follows.

1 While the kettle is boiling, preheat your mug or teapot by filling it with hot water from the tap. Tea added to an already warm container stays hotter longer and the heat releases more caffeine and antioxidants.

2 Ideal mug? Something short and sturdy (‘almost spherical’), because this has less surface area and therefore retains heat longer. Francl uses porcelain mugs ‘with a nice thin rim’, but double-walled glasses also work.

3 Pour the hot water from your pot or mug and pour the boiling water over loose leaves or a tea bag. (Francl prefers loose, but if you use a bag, choose the largest size so the leaves can get more movement. The shape of the bag doesn’t matter.)

4 Francl warns against steeping too long: most tea loses all its caffeine and antioxidants within a minute of steeping. (For decaf, she recommends steeping a regular tea bag in boiling water for 30 seconds, pouring out the water and reusing the tea bag in fresh boiling water.) Stirring is also critical, especially if you’re using tea bags. Submerge and squeeze them while brewing as it reduces the sour-tasting tannins.

5 Then milk. Francl takes hers without, but science suggests it’s best to add milk last. It reduces the chance of curdling. For the same reason, she says the milk needs to be warmed slightly. Just enough so that it is not chilled, but not so much that it is frothy.

While I talk to Francl, I also have a cup of tea – my fifth or sixth of the day – with a biscuit. What does she think about the dunking, I wonder? “Oh no,” she says firmly. “I don’t like crumbs.”

Other Francl-approved tea tricks include eating grapefruit with your cup of tea (this increases the time caffeine stays in the system) and adding a small squeeze of lemon juice to remove any ‘foam’ from the surface. Francl drinks about four cups of tea a day. In fact, the day the US Embassy tweeted about her book was the first time she had given up tea in about fifty years. “I was too busy!”

She brews them herself – “I don’t trust my wife of 31 years to make me a cup” – but dreams of “someone appearing at my bedside every morning with the perfect cup of tea on a tray.” But I haven’t been able to train the cat to do it.’

Infused: The Chemistry of Tea by Michelle Francl is published by The Royal Society of Chemistry, £20. To order a copy for £17 until April 7, visit mailshop.co.uk/books or call 020 3176 2937. Free UK delivery on orders over £25.