Tuesday, February 15, 2011

Cuppa tea

I’m a big fan of black tea due to my English heritage, where you weren’t supposed to leave the breakfast table if there was still tea in the pot. For one of my badges in Cubs I had to prove at the age of seven that I could brew the perfect cup of tea: pre-warm the pot, add x teaspoons of leaves (x = one teaspoon per person + one for the pot), add boiling water, stir, leave to brew for five minutes, pour into cup through tea strainer. Haven’t lost the art.

Why does tea contain caffeine?

It is quite natural for you to assume the caffeine in tea is there just to give you a lift. The tea bush in China was producing caffeine long before humans came by. Its caffeine is to dissuade bugs from nibbling on the leaves. You are drinking a form of pesticide! Don’t worry, all plant foods produce compounds to try and keep the bugs at bay. Some produce compounds to keep humans at bay. For example, chokoes, which are sometimes passed off as edible.

Making your tea leaf

There are different ways to prepare the tea leaf. For black tea, leaves are macerated, allowing the enzyme phenolase within leaf cells to mix with polyphenolic compounds, and left for a few hours to ferment. The leaves are then heated to halt the action of phenolase (enzymes, being proteins, are denatured by heat). Voila! You have black tea, a favourite in the UK, NZ and Australia.

Green tea, an Asian favourite, and white tea (from the youngest bud and two top leaves) are heated before any fermentation occurs. Oolong tea is fermented for only 30 minutes before being heated. All four teas come from the same plant, Camellia sinensis. All four teas have flavonoids, those antioxidant compounds that have created an excited stir in the science world for the last 20 years.

The type and amount of flavonoid polyphenols in tea differ depending on the type of tea and area it is grown. Right now it is impossible to suggest that one type flavonoid had an advantage over another; they probably have multiple positive actions. Thearubigins are the main pigments in black tea. They contribute most of the colour, as well as the astringency and “body”, of the tea.

Caffeine

All four teas also contain caffeine. Love to have a nice bottle of Grange Hermitage for every time someone said to me that they take green tea because they are avoiding caffeine. The caffeine levels of each tea are similar at the leaf level, with white tea being the lowest, around 15mg per brew, because it is usually steeped for a short period. Green tea has around 40mg/cup after three minutes brewing, while a strong cup of black tea may have 60mg of caffeine.

How much caffeine will be present in your cuppa will depend on how long you brew the tea, type of tea, how much tea you brew and possibly even the region the tea was grown (Assam in north east India had the highest leaf level of caffeine in one study).

What does it all mean?

For a long time both tea and coffee unfairly had a bad name, mainly due to their caffeine content. Herbal teas were seen as a “healthy” substitute because they don’t contain caffeine. The consensus is that 300-500 mg of caffeine a day is no threat to healthy adults, although for some even 150 mg of caffeine can disrupt sleep.

Tea is the second most widely consumed drink in the world. No, Coke is not the first, it’s water. Being so popular, tea has attracted a lot of research, some of it showing that tea drinkers have less risk of heart disease, Parkinson’s Disease, type 2 diabetes and even have stronger bones. It is way too early to say that every cuppa will definitely help you to avoid disease, but the comforting thing to me is that nothing suggests that having a few cuppas a day is a problem.

You want to hear a number don’t you? OK, there is broad agreement that up to five cups a day is healthy. Just do what I do – choose big cups.


Reference: Coultate T. Food: The Chemistry of its Components, RSC Publishing 2009

2 comments:

Chris said...

Glenn - another great post. Loved the comment about chokos being passed off as edible. I once said to someone that life was too short to eat chokos, no matter how healthy they are....

Glenn Cardwell said...

Can only agree Chris. Great for compost though.