Oxidation & Fermentation in Teas

Tea leaves undergo oxidation and fermentation to bring out their unique aromas and flavours. What is the difference between oxidation and fermentation in teas?

All teas originate from the camellia sinensis plant. Through years of grafting, unique flavours and aromas are discovered. Before the leaves become tea leaves that are consumed, they undergo carefully timed processes of oxidation and fermentation to produce the different types of teas that we enjoy – white, green, black, oolong.

Oxidation in teas is a process where tea leaves are exposed to the air to darken and dry, similar to how apples turn brown when left exposed to air. Green tea is barely oxidised, while black and dark teas are full oxidised. Oolong teas are semi-oxidised, this category ranges from lighter green (5% oxidation) to darker brown.

Fermentation involves microbial activity that breaks down the tea leave, much like yogurt, beers, and kombucha, temperature and humidity are carefully introduced during the process of tea fermentation. Aged pu-erh tea is an example of tea that undergoes aging and fermentation after oxidation. Similar to wine, the flavour of pu-erh grows in complexity and depth as it ages, so does the price of matured tea correspond to its rarity.