Tea Science 101: Oxidation, Not Fermentation

While sitting inside the loveliest tea house I had ever been in, I read their tea guide which explained that the difference between green and black tea was fermentation.

“What? No!” I exclaimed loudly to my friends, who were trying to enjoy their beverages. “Regular black tea is oxidized, not fermented! How can a tea house get it wrong!” My friends shushed me and didn’t think it was a big deal. But I wrote a long explanation on a comment card when we left.

In another tea house bathroom, they had a wall display that also stated this fallacy. I took my pen and boldly crossed out “fermentation” and wrote “oxidation” in its place. There. At least the ladies would be informed of the truth in that establishment.

Green, black, white, oolong, and pu-ehr tea all come from the same plant: camellia sinesis. Yet the tastes are different depending on the growing location, harvesting techniques, and most importantly, how they are processed after picking.

Most teas are dried in different ways with different levels of oxidation happening. There are teas that undergo fermentation, like pu-erh. Who cares? I do. If a book, company, or shop is going to bother explaining the science behind their product, get it right!

So what is the difference between oxidation and fermentation? I’m going to step away from tea for a moment to explain, since the tea videos I found are boring and/or interchange “oxidation” and “fermentation” as if they were the same thing. If I leave my metal bike outside in the rain, it will rust. That’s oxidation.

If I coat my bike with sugar and let some wild bacteria start to grow…then I have a bad example. Nevermind. Back to drinks.

Fermentation involves bacteria or yeast that eat sugars to produce carbon dioxide, and in the case of yeast—alcohol. Beer is made with fermentation. If you let beer oxidize, sadness. The difference is important! Here’s a video about fermentation and an example of making soda.

They are two completely different chemical processes and anyone who is in the tea business should make it their business to get the science correct. Science literacy and delicious tea forever!