Monthly Archives: September 2013

Some Notes on Oxidation

Back in the old days I wrote a post on Dobra Tea’s blog about tea and oxidation. This is an updated version of that post.

If you have learned a little about tea processing, you have doubtless come across the saying that Black tea is more “fermented” than Green tea. This is more than a little inaccurate, as you’ll see below.

When an apple or banana is cut open, its inside surface is generally white. Once exposed to air, however, the interior begins to change to brown and eventually black. The flavor of the fruit changes as well. This process is an enzymatic reaction called Oxidation. Many plants experience this darkening when parts of their cells are exposed to oxygen, including tea leaves.

Photo by Midori.

Photo by Midori.

When a tea leaf is bruised during the rolling process, the contact of the polyphenol oxidase in the cells of the leaf with other parts of the leaf’s chemistry begins a browning process. This process changes the leaf from what we know as Green Tea to what we call Oolong Tea, and eventually to Black (or, as the Chinese call it, Red) tea.

Gently rolling oolong tea to encourage oxidation.

Gently rolling oolong tea to encourage oxidation. San Lin Shi, Taiwan.

When an apple is cut, there are several options we can use to stop its oxidation and retain its white color and fresh flavor. Applesauce, for example, does not turn black. This is because when heat is applied, it deactivates the enzymes necessary for the reaction to continue. This principle was discovered by early tea producers and used to stabilize or “fix” the tea leaf at a desired stage of oxidation. For green tea, the leaf is heated almost immediately and no oxidation occurs.

The Chinese call this heating process “kill green” (Shāqīng, 殺青). When this technique was developed, tea producers didn’t understand the mechanism involved and it was assumed that the browning process was a form of fermentation. Even though scientific understanding has progressed in the thousands of years since, this term has remained in use and is still be quoted by many people in the tea industry, particularly in China.

Stopping the oxidation in Liu'An, Anhui.

Stopping the oxidation in Liu’An, Anhui.

Fermentation in Chinese is Fāxiào (發酵). Oxidation in Chinese is Yǎnghuà (氧化). Because it has become an industry term in its own right, Chinese articles discussing tea will use the term fāxiào, causing confusion for many Westerners. Making this more complicated is the actual bacterial fermentation involved in Puer tea, but that is another topic entirely.

So, to summarize, Green tea is less oxidized than Black tea, and neither are fermented. In addition, oxidation has basically no effect on the caffeine molecule, so green tea is likely to have roughly the same amount of caffeine per cup as a similarly infused black tea (but that is also a different article).

hong shui spring for fall

How to describe this tea experience? This spring 2010 Gao Shan Hong Shui (or Hung Shui) has the aroma and taste of plum and baked apricot. Caramelized layers surprise me, coming from a flaxen gold liquor. It doesn’t have nearly the darkness that I’d expect in a similarly aromatic Tie Guan Yin.

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The aroma is heavenly, especially in the mouth. I shared it with a friend in the teahouse and he pointed out, quite rightly, that while it’s undeniably roasted, it doesn’t have any hint of the sharp toast or charcoal flavors present in a Shui Xian. There’s a bit of the honey taste of a good Bai Hao, but it doesn’t come across as floral. The fruitiness is similar to a really delicious Mi Lan Dan Cong, but lighter in body.

What a wonderful mystery this tea holds!

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My heartfelt thanks to Stéphane from TeaMasters for introducing me to this tea. I suspect that I never would have heard of it otherwise. It doesn’t seem to be a popular style, and there’s still quite a lot that I don’t know about it. This particular leaf is from San Lin Shi on June 3rd, 2010 (another gift from Stéphane is knowing the exact date of harvest).

From what I know, Hong Shui (红水, literally, red water) is a process and not specific to cultivar, although as it is grown in Nantou province it probably is mostly Qingxin. The leaves are more oxidized than a standard Dong Ding style, and are then more deeply roasted. The roast is clearly done very carefully, though, to avoid any overly toasted taste creeping in.

All of this meshes nicely with what Stéphane has written, so if you’re interested in more on the topic, please read his blog.

Old Tea: 2010 Winter Alishan Jin Xuan

Another among the teas I decided to test in my grand (old) tea tasting experiment of this summer.

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Another Ali Shan Jin Xuan (I have a lot), these particular leaves are the last remnants of one of my favorite teas of all time. Unless I’m misremembering, I purchased this tea from DigniTea in Taipei, a family-run tea company specializing in different styles of tea from Ali Shan. Here’s my glowing review from 2011:

Golden straw liquor, aroma of fresh lillies with a slight hint of something richer: a gingerbread sweetness. Flavor is buttery sweet lightly grilled asparagus with a gentle dryness in the finish. The aroma in the mouth lingers for quite a while.

My friend and I had been wandering around the Guting station area of Taipei looking for a specific tea house we had read about when we came across this small shop. It looked promising, and within minutes of entering we were sitting at the rather modern bar inside and discussing tea styles and preparation with the wonderful proprietor. She told us about her family’s business and how all of their tea was from Ali Shan, although they had many different varieties.


For the sake of adventure, I brought back with me some winter Jin Xuan (Jin Xuan is a Taiwan-invented cultivar), spring Jin Xuan, Nitrogen-packed Qing Xin (apparently the nitrogen causes the leaves not to change as much after packaging as the standard vacuum-seal), a black Ali Shan, and an Ali Shan GABA tea (Nitrogen-flushed).

I have been extremely happy with all of them!

Now, oolongs of this style often reach their height after 6 months to 1 year of age (assuming good storage), and that definitely held true in my case. For over a year after bringing the packages back from Taiwan, I turned to my DigniTea when I was looking for something really special. As the supply of this Jin Xuan, my favorite, neared its end, I transferred the last leaves to a metal tin to (I thought) better preserve it.

This is always the danger with a beloved tea: you try to keep it alive long past its time. I’m not certain the reason for it, but after a good long life this tea has changed for the worst.

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My first infusion was for 1.5 minutes with near-boiling water, usually a good bet. The roasted aroma was present, but seemed very light and the color was pale. When I tasted it, though, I was very surprised by the taste. The best word I could come up with to describe it was “soapy”. The creamy delicious sweetness had become a sort of sour taste that was definitely not pleasant. Just in case, I made a second infusion, paying more careful attention to the leaves. The results were the same, soapy, in fact it became more pronounced. I didn’t even bother with a third.

Alas for the fine teas in our life! This is a lesson of impermanence in life, certainly. If you find something worth enjoying, enjoy it fully while it is here! If you hoard it, it may be lost, or changed into something else entirely different from the character you cherished. So it was with this tea. I humbly thank it for the lesson.

Old Tea: Pinglin Bao Zhong

This is the second tea I decided to test in my grand (old) tea tasting experiment of this summer.

Another from Taiwan in 2011, drinking this tea is always a step back to rural Pinglin. We had taken a bus to the town hoping to find a plethora of tea shops, but we were surprised at how quiet it all was.


Just next to our bus stop, we found one of the ubiquitous shops that occupies the bottom floor of a two-story house with a large garage door. When the garage doors are closed (and sometimes when they’re open!), you can never tell if it’s someone’s living room or a shop. In this case, it was a family tea business.

A husband and wife bustled around amid a hundred large plastic bags of tea that filled all available space, while the grandmother sorted some tea in the corner and kids ran about in back. The eldest of the children spoke some english, so when our intention was made clear, he was the one to serve us some tea on a beautiful tea table hidden behind some piles of dried Bao Zhong leaves. Not only was the table beautiful, but the family had quite a collection of teapots and gaiwans as well. The tannin-stained matte textures on the yixing showed quite clearly that they had seen many years of good use.


We had many good pots of tea at that shop, and purchased plenty to take back with us. My favorite was a roasted Bao Zhong which is the subject of this post.


What’s interesting about this tasting was that I had apparently saved the tea in several places. I have the original foil bag, still about one quarter full, and I had two different small tins which I use when traveling. The tins are good quality and both seal quite well and yet when I infused the tea from those, it was bland, and only a distant memory of that roasted oolong from which it came. I had planned to mark off the rest, but when I came across the bag, the tea inside had such a delightful aroma that I just had to try again.


I’m glad that I did! The aroma was the same that you smell walking around Pinglin or Maokong, sweet roasted tea. I can hardly explain what it’s like to be surrounded by it. It infuses you. If you’ve ever had the opportunity inhale the aroma of a pot of quickly heated roasted oolong, you’ll know what I mean. If not, the closest parallel that I can imagine is something like roasted chestnuts. Rich and comforting. In the mouth, the taste is flowery and actually seems to intensify as it cools. Bao Zhong is a lightly oxidized oolong and so it tends to do best at cooler temperatures.


The overall experience is light but correctly so for a tea of this style. I think one of the difficulties that I’ve had with Bao Zhong is using sufficient leaves in the gaiwan, since they are twisted in a way that makes it appear as though you’ve got more in there than there really is. It may be that when tasting the other packages of this tea, I simply didn’t use enough leaf and the resulting tea couldn’t generate enough body to seem worth considering. I also wonder if the typical foil pouch has some qualities that perhaps make it a better storage medium than even an airtight metal tin. Maybe this tea really needs to breathe. This definitely gives me something to experiment with in the future.


Altogether, this one’s a keeper. Really, it’s amazing that a lighter oolong such as this lasted longer than some of the rolled ones I’ve been trying. But that’s all just part of the mystery of tea, I suppose.

Note: I’ve written about this tea before.