The whole concept of aged white tea cakes is sort of a curious thing.
To make a tea cake, white tea leaves—a finished product that is already relatively rare and fairly pricy—are reprocessed. This process, in which the tea leaves are steamed and then compressed into a mold, "destroys the bud and leaf tissue of white tea" (Zhihui Wang et al. 2022). The cake then sits around for years while microorganisms go to work.
Why would anyone do this?
Well, if a tea producer has so-so white tea leaves, they could sell them as a middling grade of tea. Or, they could compress and age them, ideally ending up with a superior—and lucrative—product.
My last post introduced white tea cakes and looked at the various reasons, including the above, that they exist. But now we move on to the next question.
DO tea cakes improve with age?
White tea leaves are the least processed of teas. During harvest, withering, and packaging, great care is taken so that the leaves are not damaged. High-quality white tea buds and leaves remain mostly intact, and are fluffy due to the retained fine hairs on the buds and immature leaves.
These teas are valued for their high polyphenol (antioxidant) content and their floral, fruity, fresh, and clean aroma/flavor, which is due to their alcohol and aldehyde composition.
When white tea leaves are heated by steam and forced into molds, plant cells are crushed and their walls broken, allowing cell contents to interact with each other and with air. This interaction continues while the compressed leaves age, and the balance of components changes, altering aroma/flavor.
Zhihui Wang et al. (2022) determined that over storage time:
- alcohols decrease
- hydrocarbons increase
- aldehydes initially increase and then drop
- the elements that cause floral and fruity aromas decrease, sometimes substantially or totally
- unsaturated alkenes increase
The amount of alcohols, hydrocarbons, aldehydes, esters, and other components are continually in flux as the cakes age, which is why you'll have a different tea each year that you sample a cake. Overall, alcohols peak in the first years, esters during 7–13 years, and aldehydes after 16 years.
These changes cause this progression (Zhihui Wang et al. 2022):
- "sweet, fruity, and floral (1 year)"
- "sweet, fruity, and stale flavor (3–5 years)"
- "stale flavor, fruity, and woody (7–13 years)"
- "herbal (16 years)" (Note that others may describe aged white tea as mature, sweet, mellow, thick.)
During storage, bacteria and other microorganisms work on metabolites in the leaves. Zhuihui's team continued to examine this phenomenon:
Our research group previously reported the bacterial diversity in white tea (white peony) during storage for the first time, and claimed that the diversity and relative abundance of bacteria in white tea in different years were high, with the diversity tending to increase with the number of storage years. (Zhihui Wang, et al. 2023)
Note that bacteria do not work methodically in a linear fashion. Rather, they may be very active in some years and less active in others.
Polyphenols also come into play here. Powerful antioxidants, polyphenols are also antibacterial. Thus, in the first years of aging, the leaves seem to contain enough polyphenols to inhibit bacteria. However, polyphenol levels decrease over time, which means antioxidant capacity drops, and bacterial activity increases.
Zhihui Wang's team found that ten years is a tipping point of sorts, the point when polyphenol levels drop and bacteria proliferate, both in number and type. They also showed that the primary bacteria types change at around eleven years, and again at seventeen years. All bacteria were akin to those on loose white tea leaves, but were different from those found in pu-erh raw or ripe tea or fu brick tea (Zhihui Wang et al. 2023).
The potential health benefits of tea are largely due to its high polyphenol content. Since aged white tea contains fewer polyphenols than loose white tea, does that mean it's also less healthy for us? Not sure.
Caffeine levels also decrease as compressed white tea ages (and by the way, caffeine provides flavor as well as potential health benefits). Loose white tea, especially when composed of buds and the immature leaves, inherently contains the most caffeine. However, because the tender leaves must be brewed at lower temperatures (e.g., 158°F), less caffeine is extracted into the liquid.
Aged tea cakes contain less caffeine but are brewed at higher temperatures (e.g., 194°F), which extracts more caffeine. If caffeine levels matter to you, it's probably a draw. (Note that the only way to really know how much caffeine any tea has when it's brewed is to test that liquid in a lab.)
The above photo is the second brew from a white tea cake. My next post will consider additional drawbacks to compressing white tea leaves.
Sources:
–Zhihui Wang, et al., "Identification of characteristic aroma and bacteria related to aroma evolution during long-term storage of compressed white tea," Front. Nutr. 9. December 2022.
–Zhihui Wang, et al., "The relationship between bacterial dynamics, phenols and antioxidant capability during compressed white tea storage," LWT 74. January 2023.
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