The word "fermentation" is a problematic term. In beer, wine, and spirits-making, it refers to a period where a fungus called saccharomyces (spp.) is encouraged to consume the sugars in a sweet liquid, converting these sugars to alcohol and other chemicals. In miso- and natto- making, "fermentation" refers to a period where certain bacteria (bacillus subtillis) or fungi are allowed to work on the food to create certain substances, byproducts, and flavors. In coffee, fermentation describes a period where various wild yeasts and bacteria are allowed to settle on the mucilage, having the effect of dissolving it. All of these are very dissimilar processes. The micro-organisms are different, the techniques are different.... in fact these types of "fermentation" have only one thing in common: the food is allowed to sit around for awhile, during which certain microorganisms and substances transform the food at a microscopic level. Therefore, the most appropriate and accurate definition of "fermentation" might be "letting food sit around for awhile while it rots just a little bit". "Fermentation" is used in this sense when making yogurt, cheese, bread, vinegar, buttermilk, kimchee, sauerkraut, soy sauce, and when curing tobacco.
What happens during the tea process fits this broad definition of fermentation, in that the tea is allowed to sit around for awhile after being rolled or crushed. During this time, a number of interesting things happen. One of these involves polyphenol oxidase, an enzyme that oxidizes and creates melanins, turning the tea leaves brown or black (this happens in many plants. This is the enzyme responsible for apples turning brown, aging coffee turning brown, and cut vegetables of all types turning brown or black). This is related to the creation of theoflavins, the compounds partially responsible for black and oolong tea flavor. This kind of enzymatic browning relies on oxygen to happen. The crushing of the tea exposes plant materials to oxygen, allowing the melanins, theoflavins, and other compounds to be created.
So, in my opinion, oxidation is probably a more accurate term than fermentation, although you could say that oxidation happens during the fermentation (tea sitting around and rotting a little bit) period.
Last edited by Peter G
on Tue Jul 08, 2008 7:46 pm, edited 1 time in total.
Specialty Coffee Association of America