Oxidation

I briefly mentioned oxidation in my getting sorted post when I was talking about the different categories of tea and thought it might be worth talking about a little more.

Oxidation is basically what causes the leaves of the tea plant (that are green when they grow) to turn brown. It is a biochemical reaction which involves the absorption of oxygen (like when an apple is cut). Black tea is generally close to fully oxidised, Green teas are usually non-oxidised and Oolongs tend to be partially oxidised to varying degrees. Oxidation is pivotal to the processing of tea and will change its colour, smell and flavour.

Oxidation Chart

Oxidation Chart (Source)

Oxidised teas, are bruised (from lightly to extensively)  to break the  cell walls and allow the enzymes in the leaves to cause natural oxidation reactions. Heating the leaves stops oxidation by deactivating the enzymes. In this way the tea producer can decide on the extent of oxidation by introducing heat. Green teas are non-oxidised and so are heated early in the production process so that the oxidation process is skipped.

Sometimes tea-oxidation is called fermentation but no microorganisms are used so this is a misnomer. Generally when people talk about tea-fermentation they are talking about oxidation.

However, just to complicate matters, the proper micororganism fermentation does take place with pu-erhs.

There are exceptions to this, but here are the usual oxidation and fermentation levels:

Black tea – almost fully oxidised

Oolong tea – partialy oxidised (ranging from 12% – 80%)

White tea – minimal oxidation

Green tea – No oxidation

Yellow tea – No oxidation

Pu-erh – fermented (sheng pu-erh is not oxidised but shou pu-erh is)

Ti Kuan Yin – Iron Goddess Tea

I seem to be on an Oolong kick at the moment and this Ti Kuan Yin (aka Iron Goddess or Tieguanyin) is my tea-of-the-minute. I love it because it has a clean, fresh taste and sweet after-taste that is both strong and gentle at the same time. This tea is a variety of Oolong tea and comes from Fujian Province in China (this type of tea is also produced in Taiwan). Judging by the look and colour, the one I have is not a high grade Tieguanyin but it still gives a good idea why this tea is so popular. Apart from the taste, I like seeing the dark green semiball-rolled leaves expand out after it has steeped a few times but again, because this is not a high grade the leaves are chewy and broken rather than full green leaves when it is steeped.

Tieguanyin (5g) before and after steeping

Tieguanyin (5g) before and after steeping

This Tieguanyin is described as “old style” and is darker so it had medium to heavy oxidation (oxidation being the process that causes the tea leaves to turn brown).

Second brew of Tieguanyin

Amber colour of the second brew of Tieguanyin

Preparation: To prepare this tea, I put 5g of the tea in a warmed clay teapot (one that I keep for Oolongs). I add a little water that is just below boiling (when it makes the rumbling sound) to rinse the leaves. This water is poured off and disposed of, not drank. Then I add about 175ml of the hot water which is about the size of the teapot and let it rest for 30 seconds. This is the first brew and is pale yellow in color and has that lovely sweet smell but the second and third steeping are  even better with the colour turning to a deeper amber.  I usually leave these to steep for about 40 seconds each. The steeping time increases for each subsequent steeping and I find that I can get 4-5 steepings from this tea. The taste is clear and refreshing with a deeply sweet aftertaste.

If you don’t have a clay teapot or a gaiwan, don’t worry. Steeping this tea works just as well with a brew basket but if ever there is a tea that can’t be used with a metal tea ball, it is this one. The leaf expands so impressively, it would be a real shame to keep it in a confined space.

I bought this tea from Tea Palace, London and it was a reasonable £10 for 100g.