Suppose a tea vendor or processor somewhere in China or Taiwan is going through his storage room and finds a container of tea that has been sitting there for more years than he can remember. Knowing that tea cost him something, and looking to recover that cost, he comes up with an idea: “I’ll call it aged tea, and sell it for a higher price!”
Many people, even tea professionals have no clear understanding of what happens when teas like wulongs are aged. Some believe aged wulongs are a gimmick. Others are convinced time is solely responsible for the changes in oolongs. Others would say it is a matter of relative exposure (or lack of expose) to air, humidity, or roasting.
But there is actual lab research that can shed light on how aged tea changes, and how those changes can create a superior aged wulong.
What Actually Changes In Aged Oolongs?
Studies suggest that aged wulong does have different components than newer wulongs – when the tea is aged in certain ways. A sample of Taiwanese oolongs ranging in age from approximately 3 to 6 years were re-heated every 3 – 4 months for periods of approximately 10 hours each time. The key contributor to differences in the aged wulongs was exposure to heat. The research showed that heat, much more than time, changed the chemical components of aged wulong.
One of the original purposes of re-firing wulongs was to remove moisture that the tea had re-absorbed from the air. Re-firing the tea gave it a longer shelf-life. It turns out that heating process was doing more. It was responsible for breaking down EGCG into simpler compounds and contributed to greater proportions of the flavonols kaempferol, myricetin, and quercetin. The presence of these flavonols MAY give some credence to the belief that aged oolongs offer superior health benefits.
A second study showed that flavor compounds changed too. Long straight chains of alcohols and acids were broken down, and nitrogen-containing pyrrole and pyridine compounds were created.
At least one of the studies also looked at teas that were stored but not re-fired, or were re-heated less often or less intensely. Storage alone was found to cause much less alteration in the teas. In fact, they more closely resembled fresh wulongs in chemical composition.
What This Means
For people who want to buy aged wulongs, but are uncertain of what to expect, or how to evaluate aged oolongs, the studies offer a few tips.
1. The re-roasting associated with aged wulongs contributes more than time. When determining which aged tea to buy, it may be more useful to know how the tea was re-roasted than how old it is.
2. Re-heated oolongs had darker colored leaves and liquor. The studies noted how the dry leaves of the re-roasted tea were nearly black, and could not unfurl as easily as stored teas that were not re-roasted. In the particular Taiwan oolongs used in the study, stored oolong that was not re-heated had liquor color much closer to fresh tea liquor, and their leaves more easily and more fully unfurled during steeping.
3. Re-heated oolongs will taste different. The re-heating process creates or alters chemical compounds in such a way that develops a more sour taste, caramel, sweet corn, and baked aromas. As with color, the stored teas that were not re-heated did not significantly exhibit these characteristics, and exhibited aromas more similar to fresh wulong teas.
Changes In Volatile Compounds Upon Aging And Drying In Oolong Tea Production. Kuo et al. J Sci Food Agric 2011; 91: 293-301.
Massive Accumulation of Gallic Acid and Unique Occurrence of Myricetin, Quercetin, and Kaempferol In Preparing Old Oolong Tea. Lee et al. J. Agric. Food Chem. 2008, 56, 7950-7956.
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