Tea - Fermentation vs. Oxidation

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Tea - Fermentation vs. Oxidation

Postby Jon Brudvig on Tue Jul 08, 2008 1:21 pm

It seems there is a whole lot of conflicting tea info online. Some sources say that fermentation and oxidation (in reference to tea processing) are interchageable terms, and others say that they are definately different and should not be confused with each other.

Which is it?

And can someone point me to a good, definitive tea resource?

Thanks!
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Re: Tea - Fermentation vs. Oxidation

Postby Matt Milletto on Tue Jul 08, 2008 1:44 pm

I built the website www.planet-tea.com a few years ago, and there is some good information on there. Not sure how detailed it gets into oxidation vs. fermentation. From what I understand, oxidation, and the amount of oxidation is what defines teas as White, Green, Oolong and Black ... the longer the leaves oxidize or are rolled means the darker the tea, and more caffeine there is. From the below chart, it seems that oxidation and fermentation are separate, but closely connected ... Here is a flow chart I built for different tea processing methods that may be of some help:

Image

Two weeks ago, Chris Rosen from Pekoe Sip House in Boulder, CO attended our 4 day class at the school, and we spent our spare time discussing tea and how complex it is. I learned a lot from him, and his company is on the cutting edge of the tea industry. They travel to farms and create direct trade relationships with many countries, similar to direct trade coffee relationships.

Chris would be a valuable resource to the board for sure, Alistair email me and I can get you his info.

- Matt

Image
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Re: Tea - Fermentation vs. Oxidation

Postby John P on Tue Jul 08, 2008 4:32 pm

I would add that Oolong tea is not just a particular oxidation and process of tea.
Oolong is a specific varietal, or cultivar, of tea that is specific to the Fujian province of China, and Taiwan. The more highly regarded Oolongs come from Taiwan.

Oolong is referred to as a "Qing Cha". (blue-green tea). Qing Cha cultivar, as best as I know, came from the Wuyi Mountain area in the Fujian province of China. When those from southern Fujian left China to form a better life in Taiwan, they took some of the tea trees with them as well.

In Taiwan Oolong, as a Qing Cha, grows above 1200 meters and ranges in oxidation from almost zero to nearly 70%. After that it is how it is processed... dry, pan roast, dry... It is the combination of the Qing Cha cultivar and the process that makes it an Oolong tea.
You can have 'White Oolong', 'Green Oolong', and 'Oolong' based on the specific fermentation of the Qing Cha.

This is off the top of my head so I may have missed something.

...My wife is Taiwanese and one of the most prized teas, "High Mountain Tea" grown on Mount Ali, hails from Chiayi, the same city/county her family lives. This is what was explained to us in Taiwan where we source many of our teas directly.
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Re: Tea - Fermentation vs. Oxidation

Postby Peter G on Tue Jul 08, 2008 7:05 pm

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.

Peter G
Last edited by Peter G on Tue Jul 08, 2008 7:46 pm, edited 1 time in total.
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Re: Tea - Fermentation vs. Oxidation

Postby Ric Rhinehart on Tue Jul 08, 2008 7:38 pm

One of the other things that the "fermentation" processes described above have in common is the production of alcohols, esters and notably, CO2. In tea, while there may be some minimal production of CO2, this is not a definitive byproduct of the process. The better defining term is oxidation, especially since the presence of oxidase enzymes in the dermal layer of the tea leaf is the driver of the color change, flavor change and creation of the complex melanoidans and polyphenolic chains that contribute so much to flavor in oolong and black teas.

To suggest that oolong teas are specific to Taiwanese varieties would probably make some Formosa manufacturers happy, but would be wildly innaccurate. Ti Quan Yen, the iron goddess, probably developed in mainland China and was exported to Taiwan. The mountain cultivars of camellia sinensis grown there make exceptional oolongs, but they are not alone in claiming the name. The best answers for the name game are going to come from chinese linguists, not from tea makers.
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Re: Tea - Fermentation vs. Oxidation

Postby John P on Wed Jul 09, 2008 3:22 pm

Ric,

you are correct. Tie Guan Yin came about in the 15th Century, and the tea cultivating culture did not begin to really shape itself in Taiwan until the 18th century.

But in overall terms of oolong tea. It is Taiwan's unique geographic position and it's mountainous topography coupled with their improvement in the cultivation and processing that gives Taiwan's oolong teas unmistakable character and flavor from nuanced fruits, to honey, to golden raisin. Taiwan's prized "extra fancy" oolong tea is known for its light buttery mouthfeel and its disinctive sweet peach and floral notes.

Fujian oolong tea and Taiwan oolong tea are really two different animals... sort of like Guatemala Antigua Yellow Bourbon and Brazil Cachoeira Yellow Bourbon. Different climate, different processing, and although both are enjoyable, the result in the cup is quite different.

For the Fujian teas, I prefer the Silver needles. And if you hop over to the Yunnan area, there are some of the world's best teas in those mountains.

I think I'll go have some coffee. :D
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