An expert chemist’s guide to brewing the perfect cup of tea

When it comes to crafting the perfect cup of tea, lovers of the brew know it’s as much about flavour and ritual as it is about comfort and connection. From black to green, oolong to herbal, every cup tells a story. But what if we told you that behind the soothing steam and fragrant leaves lies a world of chemistry – one that can actually help you brew a better, more flavourful cup?  

According to Michelle Francl, professor of chemistry at Bryn Mawr College in Pennsylvania, USA and author of Steeped: The Chemistry of Tea, brewing tea is a rich chemical process involving hundreds of compounds that influence the colour, aroma, taste and even health benefits of every cup.  

“Tea is the world’s most popular beverage. What many people don’t realise is how complex the chemistry behind it truly is,” she said. 

While most South Africans reach for red Rooibos, the green, unfermented version actually has higher antioxidant levels.  

“Fermented Rooibos has fewer antioxidants, because the fermentation process is essentially an oxidation process. Antioxidants act like little sponges soaking up oxygen. Once they’ve reacted, they can’t function as antioxidants anymore,” Francl,added.  

Green Rooibos retains more aspalathin, a rare and potent antioxidant unique to the plant, but one that degrades with time and oxygen. Her advice? “Drink it fresh.” 

Francl also cautions against using mineral-heavy water. In teas made from Camellia sinensis, it can result in “tea scum” – a layer of compounds floating on top of your brew. She suspects something similar may occur with Rooibos if the water is particularly hard.

“These mineral-polyphenol interactions can dull flavour, while filtered water can help preserve the taste profile.”  

Many Rooibos drinkers report that longer steeping enhances sweetness. Though there’s no formal analysis to confirm this, Francl says it's plausible.  

“Longer steep times increase the presence of maltol, a natural flavour enhancer and vanillin, the same compound that gives vanilla its signature sweetness.”

To brew the ultimate cup of Rooibos, Francl recommends the following:

•       Use green Rooibos if your goal is to maximise antioxidant intake
•       Choose fresh Rooibos to retain aspalathin content
•       Use boiling water (100°C)
•       Steep for 10 minutes
•       If possible, opt for filtered water to avoid flavour-dulling minerals

Whether you're sipping Rooibos to unwind after a long day or seeking its health benefits, knowing the science behind the steep can elevate your tea ritual.  As Francl so elegantly puts it, “Brewing tea is not just an art. It’s a beautifully balanced act of chemistry.” So next time you brew a cup, give it the full ten minutes and let science do the rest.