Unfortunately, scientists get lazy sometimes too sometimes. In the past, studies have sought to compare chemical profiles of two or more different tea types, but in doing so they used tea samples from entirely different backgrounds. For example, people often ask whether black tea has more caffeine than green tea or vice versa. In a poorly designed study, the researchers might try to answer this question by measuring caffeine content in a green tea from Japan and a black tea from Kenya. This study would tell us next to nothing about whether the processes required to make green teas leads to more or less caffeine compared to processes required for black tea production. The caffeine contents of the Japanese green and the Kenyan black tea almost certainly will vary from one another, but not because of their mere processing into green or black tea. Their cultivation style and genetics explain most of the variation in caffeine content (cultivar, terroir, growing season, vintage, fertilizer, the list goes on, all ultimately determine caffeine content more than processing).
So, below we have the recipe for conducting a proper experiment to measure the effects of tea processing:
To most accurately measure the effects of tea processing (and only tea processing), we must use the same batch of fresh tea leaves, then split up that single batch evenly, and then process each subgroup into their respective tea types (green, black, oolong, etc). Only after all of that can you measure compounds in those final tea products and accurately assess if tea type X has more of whatever compound (caffeine, L-theanine, EGCG, etc.) than tea type Y or tea type Z (but not tea type LMNOP).
Thankfully, this is precisely the style of experiment conducted by our friends at the Tea Research Institute in Hangzhou in order to test what is happening during white tea withering on a molecular level [1].
In this study, a single batch of fresh leaves was split evenly into three groups, and processed into green, black, or white tea. Examine figure 1, and notice the color of the leaves and the liquor. Nothing all too white about the white tea, except for the silver hairs on the buds (how white tea originally got its name). The liquor is far less light in color than that of green tea. And under the microscope…
“Catechins, including EGCG […] were at lower levels in white tea and had the lowest levels in black tea when compared with those in green tea. This result is consistent with the fermentation degree in that black, white, and green tea is fully fermented, slightly fermented, and non-fermented, respectively. However, these results are different from Santana-Rios’s findings [2], who reported that white tea had higher contents of [catechins] compared with green tea. This contrast might be due to the inclusion of different varieties of white tea and green tea in Santana-Rios’s work, whereas the same batch of tea leaves was included in this study.”
We see here that holding all other variables constant (by using the same batch of leaves to start with), white tea processing meets at least one criterion of ‘fermentation’, being that catechin content drops. Ok, what about black tea theaflavins?
“Theaflavins […] were at significantly high concentrations in white tea because of the slight fermentation, but levels were much lower than those in black tea.”
Our friends in Hangzhou have found lower green tea catechins, and more black tea theaflavins in white tea than green tea. There is yet another relevant factor… the case of methylated catechins. Methylated catechins are sort of like ‘super-catechins,’ reportedly capable of stronger anti-allergic [3,4] anti-hypertensive [5], anti-oxidant [6], anti-obesity [7], and probiotic [8] effects than normal green tea catechins, such as EGCG. Methylated catechins are particularly present in oolong teas, but not in black tea, since these catechin derivatives are consumed in the process of heavy fermentation required for black tea processing [9,12].
Several types of methylated catechins have only been able to be isolated from oolong teas [10], because methylation happens as a result of bioactive processes involved in ‘semi-fermentation.’ Methylated catechins increase with some fermentation, but then decrease with too much fermentation, taking on a bell curve shape in relation to increasing fermentation. As for the methylated ‘super-catechin’ content in the study we are reviewing;
“methylated catechins […] exhibited highest contents in white tea compared with green tea and black tea. Because methylated catechins are consumed during [heavy] fermentation, […] it is assumed that the methylation of catechins may occur during the prolonged withering process of white tea [1].”
Although total catechin content drops during white tea production, methylated catechin content increases. This means a lower total antioxidant capacity for white tea compared to green tea (as more total catechins generally means more antioxidant power in tea [12,13,14]), but this fermentation-driven change also leads to the creation of methylated ‘super-catechins,’ and methylated catechins are sweet… (figuratively speaking. their real taste profile is highly bitter and astringent. But, you know, sweet as in, “dude, my hypertension is so alleviated right now, these methylated catechins are sweeeet”).
The shift of tea polyphenols, both in type and quantity, can explain much of the variation in health effects observed among different tea types.
To recap our review of the Hangzhou study so far, we have seen that white tea withering lead to:
- Green tea catechins down
- Black tea theaflavins up
- Oolong methylated catechins up
These are all signs indicative of semi-fermentation, which makes sense, looking at white tea’s darker liquor color, sweeter, less astringent taste, and floral/fruity aromas, as opposed to grassy/green notes in a truly non-fermented tea.
TO BE CONTINUED… in part 3 we talk about how white tea develops it’s sweet and savory profile as a result of withering…