⚙️ Processing
Oxidation
The step that makes black tea black. It is called fermentation, but no microbes are involved.
What the tea trade calls 'fermentation' is a reaction driven by the leaf's own oxidising enzymes. Unlike yoghurt or miso, no microorganisms are at work; strictly speaking it is oxidation. The older word has simply stuck.
During this stage colourless catechins turn into pigments such as theaflavins and thearubigins. The green leaf turns coppery, and the colour and character of black tea appear.
Related terms