'Pickled' Tea: Awa Bancha — The Science of Post-Fermented Tea Made by Lactic Acid Bacteria

Explanation

Much of the tea we drink is either 'non-fermented tea (green tea),' in which the picked leaves are heated to stop fermentation, or 'fermented tea (black tea, oolong tea),' in which the leaves are oxidized by enzymes. However, 'Awa bancha,' produced in the mountainous areas of Tokushima Prefecture, is made using an entirely different and rare method called 'post-fermented tea.'

The distinctive feature of post-fermented tea is that it uses the power of 'microorganisms' rather than enzymes. Boiled tea leaves are packed into tubs, and under airtight (anaerobic) conditions, 'lactic acid bacteria (such as Lactiplantibacillus)' break down sugars to produce lactic acid. This is the same 'lactic acid fermentation' used in pickles and yogurt, and it is the source of Awa bancha's refreshing sourness and umami. It is also notable for containing very little caffeine.

Recent research has reported that components contained in Awa bancha may affect the activity of 'disease susceptibility genes' related to allergies, making this traditional food a subject of cutting-edge molecular biology research as well. In 2021, it was registered as a National Important Intangible Folk Cultural Property.

'Fermentation' is an important theme in science (biology and chemistry). Organizing the differences among green tea, black tea, and Awa bancha by 'who (enzymes or microorganisms)' causes the reaction and 'under what conditions (aerobic or anaerobic)' makes the distinction between fermentation and oxidation easy to understand.