Deja brew: chemistry professor’s latest advice on tea drinking – try grapefruit | Tea

If you find yourself feeling the energising effect of your morning cuppa has worn off before the bus arrives, the scientist behind controversial advice to put salt in tea has some more palatable advice: try some grapefruit.

Michelle Francl, a professor of chemistry at Bryn Mawr College, caused an international storm in a teacup last month after suggesting a pinch of salt would create the perfect brew.

Now she has a tip far less likely to reignite the biggest transatlantic row over tea since the American revolution: ways to prolong the pick-me-up. Speaking at an online webinar hosted by the Chemistry World magazine, she revealed fruit and vegetables can prolong, or shorten, the caffeine rush.

“If you eat a lot of grapefruit you can increase the time the caffeine remains in the system,” Francl said. “And if you add cabbage, broccoli and brussels sprouts to your diet you can clear caffeine more quickly.”

She said the reaction to the advice given in her book Steeped: the Chemistry of Tea had left her “bowled over” – especially the diplomatic interventions that ensued – and that the American approach to making a brew was not to her taste.

Her advice caused an outcry, and led the US embassy to London to post on X that “the unthinkable notion of adding salt to Britain’s national drink is not official United States policy. And never will be.” However, the otherwise reassuring post ended: “The US embassy will continue to make tea in the proper way – by microwaving it.”

Francl has taken issue with the American habit of using a microwave for their brew. She said the approach promoted the formation of a cloudy material, known as tea scum, composed of organic substances with calcium and magnesium carbonates.

“It happens when you microwave tea because you bring things to the boiling point so quickly, you do not remove the oxygen and the carbon dioxide. So you have more carbonates in the water and oxygen also promotes the development of the organics that lead to this raft of floating stuff.”

Francl said consternation over a previous comment – that milk should be warmed – was something of a misunderstanding, noting she did not mean it should be heated up.

“But really cold milk from the fridge dumped into hot tea can in fact curdle,” she said.

Francl said the size and material of teabags mattered, but not their shape, while it was important to warm a teapot before use to ensure water was not cooled when added.

“At 60C the total caffeine extracted is roughly half that from 90C,” she said. “[If] the water [you are] using to make your tea is not hot enough, you’re not getting the caffeine dose you think you’re getting.”

For those who like a calming cup, Francl said earl grey might be best as it had higher levels of a substance called linalool because of the citrus oil it contained.

“It turns out that linalool activates the same pain relief pathways as opioids,” said Francl. Inhalation of the aroma has been shown to reduce pain perception in mice and anxiety in humans.

“Earl grey tea with that characteristic scent is something that can reduce anxiety in humans. So when my husband has that cup of tea before his departmental meeting, he’s on to something.”

Scientists have revealed there is another important ingredient to the perfect-tasting cuppa: microbes.

In the journal Current Biology, researchers reported that different varieties of tea are associated with different soil microbes, and that varieties associated with microbes involved in nitrogen metabolism contain higher levels of the amino acid theanine – a substance that shapes the flavour of the drink.

“Our results show that the flavours of tea can be affected by soil microbes as we showed that the microbes affect the level of theanine,” said Zhenbiao Yang, a co-author from the Fujian Agriculture and Forestry University in China.

“However the microbes are unlikely to have an impact on the types of teas, which is mostly determined by cultivars and processing procedures.”