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,” notes Francl. “What many people don’t realise is how complex the chemistry behind it truly is.”
While her book explores the molecular magic in the Camellia sinensis plant – the source of black, green, oolong and white teas, for South Africans, the real intrigue lies in how Rooibos (Aspalathus linearis), our proudly local herbal infusion, compares.
“Perhaps the biggest difference between Camellia sinensis and Rooibos is the type of alkaloids they produce,” says Francl.
Camellia sinensis is a source of caffeine, along with theobromine and theophylline – all stimulating compounds that give tea its characteristic kick and slight bitterness. Rooibos, on the other hand, is naturally caffeine-free and instead produces trigonelline, an alkaloid also found in coffee and fenugreek. “Trigonelline is not a stimulant, but studies suggest it may help regulate blood sugar,” Francl explains.
This difference gives Rooibos its mellow, calming character. It’s also less astringent than traditional teas, because it contains fewer tannins – the polyphenols that create that dry, puckering feeling on the tongue.
“Overall, Rooibos is a calming beverage, with a sweet rather than bitter or astringent taste,” notes Francl.
Another fascinating fact is that teas, including herbal tisanes like Rooibos, contain a host of fragrant compounds like linalool, which gives tea its floral scent, as well as geraniol – a compound also found in roses and lemongrass. “These molecules are highly volatile, which is why freshly brewed tea smells more fragrant than one that has cooled.”
The colour of your brew also depends on pH. Francl says Rooibos, being lower in tannins and higher in flavonoids, shows less dramatic colour shifts than black tea, but by adding lemon juice (which lowers pH) it can brighten the reddish hue.
The art and science of steeping
Francl is quick to point out that steeping time and temperature affect what ends up in your cup – both chemically and sensorially.
“The longer you let anything steep, the more compounds will be extracted. Lighter, more water-soluble molecules come out first. Over time, larger polyphenols are drawn into the infusion, building a more complex flavour, but also increasing astringency.”
She also highlights that brewing temperature can influence the release of other compounds like theanine, which contributes to black and green tea’s umami flavour and calming effect. Though unlike black or green tea, Rooibos doesn’t contain theanine, steeping it properly still maximises the release of other potentially soothing compounds like aspalathin and quercetin.
So, how long is just right for Rooibos?
“For optimal antioxidant extraction, research shows using boiling water (100°C) and steeping for 10 minutes is best,” advises Francl.
Beyond that, however, the antioxidants begin to degrade due to oxygen exposure. So, timing really is everything.
Red vs Green Rooibos: A matter of oxidation
Unfermented, green Rooibos (left) and fermented red Rooibos (right)
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.”
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.”
Minerals and “tea scum”
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.”
Why long-steeped Rooibos tastes sweeter
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.”
A science-based recipe for Rooibos perfection
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.