Learn the science behind:
Tea should be as sharp as a two-edged sword and as bitter as wormwood.
It’s a well known saying about British tea, but too be honest, not very applicable to me, which is why in my last post in the mini-series on a British afternoon tea, we’ll be discussing tea!
Who doesn’t like having a high tea (or, the proper British name: afternoon tea)? A stack of small sweets and savoury snacks together with a big pot of tea. I recently enjoyed one at the Bel and the Dragon when visiting the UK. However, one of the main disadvantages for me in the UK is the tea itself, as strange as it might sound. I don’t really like the very strong bitter teas often served with a high tea.
So I generally ‘save’ my tea by removing the tea bag or leaves as soon as I can, but sometimes it’s just too late (do you dunk or steep your tea?)… Why add three big tea bags to a small pot of tea? I don’t see the necessity, but I guess I’m just not ‘tough’ enough ;-). Since tea is such an important part (after the scones, jam and clotted cream of course…) I decided to dive into tea science. What makes tea so bitter?
Making tea, its origins
Let’s start at the beginning of tea. Tea is made from the leaves of the tea plant (its scientific name is Camellia sinensis). The leaves are plucked from the plant during the harvest (which might be year-round, depending on the region).
This tea itself tastes bitter and astringent. Phenolics components (which play a role in so many chemical processes) cause this bitter taste and it serves to keep away animals.
Tea doesn’t have to be processed a lot before it can be used. The main step is drying the leaf actually so it can be kept for longer. What happens before drying is what actually determines the main flavour characteristics of the tea.
Enzymes and tea
As you might have read in my post on enzymes, enzymes are proteins which can catalyze certain chemical reactions. In other words, it can speed up reactions. Often an enyzme is specialized in one specific (type of) chemical reaction.
In tea the enzymes cause browning of the tea leaves as well as the formation of various aromatic components. The main enzymes playing a role in tea are polyphenoloxidase (PPO) and peroxidase. You might have read about PPO in my post about the browning of bananas, it’s the same enzyme!
Tea by itself contains a lot of polyphenols. Polyphenols are large molecular structures built from phenols. Phenols are a very basic type of molecules: a benzene group (this is a ring of 6 carbon atoms with 3 double bonds) and at least one oxygen side group. The high number of double bonds gives them some very special properties since these double bonds can move and jump around easily in chemical reactions.
The enzymes in tea will initiate reactions with these polyphenols which will react together and form larger and larger molecules. For those reactions they need oxygen. They are oxidation reactions, a type we’ve come by before. So many different molecules are formed that it’s hard to name several specific ones, but they generally belong to the theaflavins, theasinensins and thearubigins. The last group contains the most complex molecules which also have the darkest colour and are very soluble in water.
It is also the polyphenols (not necessarily the very large ones though) that give black tea its astringency and particular taste sensation.
Difference between green and black tea
Not in all types of tea will the enzymes actually be able to catalyze the oxidation reactions. That’s the main difference between green and black tea. Black tea is left to react with all the enzymes. In green tea the tea leaves are heated to deactivate the enzymes. Enzymes, as most proteins, as very sensitive to heat and will become deactivated.
Last but not least the (number of) tea bags
Tea bags in the Netherlands are relatively small and don’t contain by far as much tea as the British tea bags do. Furthermore, British tea is often made with 2 or 3 tea bags for just 2 or 3 cups of tea. This will allow the concentration of bitter and dark components to dissolve in the water very well and give the tea its strong bitter and astringent flavor.