Making Black Tea - Stage 3 - Oxidisation

Welcome to the third stage of my explanation about how tea is produced. From Bush to Cup. 

So far, I have described how the leaf is first withered and then rolled. This week it is all about Oxidation. The oxidation process is important because it develops the flavour and aroma of the tea. It is a very important stage as it determines the tea’s core character. 

Oxidation occurs when the freshly rolled leaf, its juices and sap, reacts with the air and an enzyme chemical reaction takes place. Theaflavins and thearubigins are characteristic products formed from catechins during this oxidation process. In the past we have spoken of why selective hand-picking is very important, coarse leaf that is not from the top two leaves and bud will lack these theaflavins and thearubigins. 

  Selective hand picking is crucial to making good tea 

Freshly rolled leaf is spread onto a cement or steel table and during the oxidation the leaf appearance will change from a green, to orange and then to brown. The thickness of spread and the oxidation time will again depend on the conditions of the wither and the current and past days weather. The temperature in the oxidation area will also play a factor and tea estates will add humidity to this area to help release more flavour from the leaves. Achieving the right spread is crucial, too thick, and not enough oxygen will penetrate the leaf, to thin and you chance drying the leaf out and killing the flavour. 

Nosing oxidised teas 

For low grown teas like New Vithanakande, a general rule is that the thickness of spread will be between 2.5 to 3 inches, and tea will be left to oxidise for between 2 to 2.5hrs. For upcountry estates that produce the smaller leaf grades of teas like Planters’ Breakfast, they pass through a Rotorvane machine to chop the leaf into smaller particles. The thickness of spread will then be between 2 to 2.5inches and left to oxidise for between 1.5 to 2hrs. 

The decision about whether the oxidisation process is complete, again comes down to the experience of the tea maker. Whilst timers are set to track the batch oxidisation time, many tea makers will "nose" the tea and smell the leaf. By nosing the leaf, a skilled tea maker will know whether to stop oxidisation or carry on for a bit longer. A batch of tea that is ready for the next stage of drying smells of freshly cut apples and jasmine flowers. 

Oxidisation tables. Click here to see a video from New Vithanakande Factory