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Enjoying the Diversity of Oolongs

By Guang Chung Lee

Guang has a PhD. in Chemical Engineering. He has been passionate about tea culture and Yixing since he studied in Taiwan. Now he lives in Houston, TX, and is the proprietor of Hou De Fine Tea.

From the ethereally fragrant Bao Zhong, smartly caramelized Dong Ding, intoxicatingly fruity Oriental Beauty to the profoundly mellow Wuyi yan chas, the family of Oolong tea offers a unique experience to all tea lovers. During the warmer months I almost always find myself reaching for an Oolong to comfort me. The fresh spring Oolongs lend fragrance and grace to the day, while their roasted or aged cousins provide depth. Since this season is for me a time to enjoy Oolong, I thought I would discuss some of the aspects of this huge variety of tea and clarify some of the processing that leads to the differences and subtleties found in the many cups of Oolong tea. In this article, I will focus on the two factors of roasting and aging, and the relationship between them and the oxidation of Oolong teas in general.

In general, Oolong teas are categorizes as teas that are partially oxidized and shaken during processing. To fully realize the diversity of Oolong tea, you need to understand the oxidation that characterizes each one. You can see from the diagram of the oxidization spectrum below that Oolong teas are usually between 30% to 70%, with Taiwan's Bai Hao (Oriental Beauty) representing the highest point in the scale. However, nowadays the high mountain Oolongs (Li Shan, Shan Lin Shi, or Ali Shan Oolongs) may have oxidation degrees lower than 30%.

Modern experimentation has created more varieties than this traditional scale can cope with. Moreover, entering the world of Oolong through an understanding of oxidation forces us to recognize the importance roasting and aging can have in creating new categories of Oolong tea. The quality scale used to evaluate each Oolong tea will be different depending on the type of oxidation used in the processing. Of course, the cultivation of the tea plants also plays a decisive role in the overall quality of aroma/taste, but unless you have a knowledgeable and trustworthy source, information about the cultivation is not usually accessible to consumers.

In order to fully comprehend the role of aging and roasting in the oxidation of Oolong tea, you can use a 3-D graph like this to qualitatively identify each tea. As an example, I used a 10-year-old Dong Ding Oolong shown as a red dot:

Understanding where your tea is in terms of oxidation allows you to compare it to similar varieties. It would take a large book to go through all the shades of different oxidation in Oolong tea used over time in different regions. We may, however, come to understand a bit about roasting and aging in relation to oxidation.


In general, finished Oolong teas may undergo additional roasting for one of the following reasons:

1. In order to lower the moisture content in tea leaves to about 3%-4%, so that the aroma and taste remain consistent over a longer period of time.

2. To remove undesired smells, especially the grassiness which is usually caused by an insufficient "kill-green (sa chin)" frying.

3. The high temperature during roasting causes complex chemical reactions among components in tea leaves. Two major reactions are: the Mailliard Reaction in which the carbonyl group of sugars reacts with amino acids; and secondly the Caramelization Reaction that causes the oxidation of certain sugars. Both reactions result in brown-colored and aromatic changes in the tea. Properly roasted teas offer an amber-colored liquor with more complex aromas than un-roasted Oolongs.

As a general rule of thumb, the degree of roasting usually aligns with the oxidation level. For example, a highly-oxidized Oolong can undergo a higher roasting to develop really robust and complex aroma and taste; a lightly-oxidized Oolong, on the other hand, is better with light or even no roasting. Though the reasons for the roasting and the changes it brings about are explained easily, the process, in fact, requires a profound knowledge of tea, highly-trained skill and great patience. It is common for roasted Oolongs such as Dong Ding to undergo several days of roasting, and some Tie Guan Yin teas can even take several weeks. Constant attention to the tea is required. Even a small error or some negligence during these lengthy roastings may ruin the whole batch of tea.

The decision of whether or not to roast is largely affected by the consumer market. Take Tie Guan Yin for example: Anxi of Fujian province in China and Pin Lin in Taipei city, Taiwan, are both renowned for their Tie Guan Yin teas, but their styles are totally different. Anxi's Tie Guan Yin teas are usually lightly roasted or not at all, as the preference there is for the intoxicating floral aroma from the cultivar. However, that aroma is considered too overwhelming by Taiwan's consumers. As a result, Tie Guan Yin from Pin Lin is still made in the traditional way, with heavy-roasting to caramelize and mellow the aroma into a more mature and fruity taste.


Enjoying old Oolongs is a rather unfamiliar experience for most Western tea drinkers. Puerh teas are generally known to get better with age, but Oolongs? Actually, great transformations can happen to Oolong teas over time. And what's more, aging Oolongs may require more care from the owner.

Firstly, it is important that we distinguish between "aged" and "expired" Oolongs, the latter having gone past their shelf life, resulting in a flat aroma and flavor. If you just leave a bag of Oolong in your tea cabinet, six months later you will just have a bag of really lifeless and uninspiring tea. Conversely, an aged Oolong has been carefully selected, roasted, and stored by the owner so that its aroma and flavor will actually improve and develop over a long period of time (maybe even decades).

A certain degree of humidity is important in the aging of Puerh, but humidity is almost always not suitable for aging Oolong teas. The chemical changes that occur in aging Puerh and Oolong teas are also different. The aging of Puerh involves very complex biological, humidity-triggered Mailliard reactions that require the presence of ambient moisture, whereas the aging of Oolong is more like a series of roastings -quenching - caramelization processes that could be repeated several times by the owner during storage. While the aging or artificially fermenting ("cooking") of Puerh has received a lot of attention and scientific research, the aging of Oolong is still largely a "household" knowledge that some tea store owners have created to cater to a connoisseur-oriented niche in the market.

Preparing Oolong teas for aging is really not as daunting task as it may seem. As long as we have the proper tools, a willing heart to learn and experiment and plenty of patience, we all can successfully age Oolong tea. The things you will need are:

1. A tea roaster. A specially designed bamboo tea roaster is the most convenient choice. Although common household roasters could also be used, it is best to have a designated roaster just for tea, in order to avoid flavor contamination from other foods. (Perhaps I will demonstrate how to use a bamboo tea roaster in a future article.)

2. A storage container. An unglazed earthenware jar, such as those made of Yixing clay, are the best choice. If that kind of jar is difficult to find, a porcelain jar or even a metal can are also suitable. One trick when using a metal can is to first place a layer of clean, unbleached handmade paper inside the can. This layer of paper not only separates the tea from the metal, but also helps regulate the moisture content,

3. A clean and cool cabinet space for storage. As with most teas, container should be shielded from sunlight.

The tea is roasted and sealed tightly In the container afterwards. It is best if the container is completely full so that the oxygen level is kept to a minimum. The lid should be sealed extra tight, In fact, many experts will seal the lid with wax to ensure complete closure, Knowing when to open the container, and whether or not to periodically re-roast the tea is the most difficult aspect of the process and only really learned over time and the experience of trial and error.

In the 1990's, when the Puerh hype was just starting in Taiwan, aged Boo Zhong teas were sometimes sold as aged loose-leaf Puerh in order to fetch a better price. Now that the consumers' knowledge has improved, a niche market has been created for them. We are fortunate to live at a time when we are seeing more and more aged Oolongs unearthed and appreciated.

Oolong tea is an art, representing the highest refinement in tea processing, and as such should be appreciated with an artistic mind. Still, an analytic understanding can also enhance our appreciation of all the skill and labor that contributes to the production of this majestic class of tea, and perhaps nowhere is that skill as masterfully demonstrated as it is in the roasting and aging of special Oolong teas.