Sunday, March 4, 2018

Oolong aroma and taste: processing or variety and terroir?

Found a paper comparing five oolongs each from Yunnan and Fujian, and comparing these to samples of Chinese green, black and puer teas.* The focus of the paper was on the oolongs, to determine whether it was Camellia variety and terroir, or the processing that most affected the sensory qualities of the resulting tea.

The Yunnan oolongs were made from Camellia sinensis var. assamica and the Fujian oolongs from Camellia sinensis var. sinensis, all from the spring 2015 harvest. Here's a picture of the teas from the article:

The teas described in the article. The authors noted that the Yunnan oolong was paler than the Fujian oolong, consistent with differences in polyphenol content.

What fascinated me was that the aromas of the two different types of oolongs were very similar and their volatile chemistry (which provides for the teas’ aromas) were virtually identical. The aromas were significantly different from the aromas of the other teas. What these reslts suggest is that it is processing that influences the aromas these teas.

By contrast, the tastes of the two different kinds of oolongs were noticeabley different, with the Yunnan being less sweet and noticeably more bitter than the Fujian teas. 

I’ve graphed the concentratiions of epigallocatechin gallate (EGCG) and total polysaccharides: 

ECGC and polysaccharide content (in
mg/g) of Yunnan and Fujian oolongs. The differences in content are statistically significant.

What you notice is that the Fujian tea has more ECGC—the most bitter compound in an oolong. So why was the Fujian less bitter than the Yunnan? My guess is that the sweetness of the polysaccharides in the Fujian tea inhibits the perception of the bitterness. 

And the other important conclusion from this paper: terroir and/or variety influenced the polysaccharide content of the teas as well as the catechin content. 

Tea leaves produce catechins in response to sunlight—these chemicals act like sunscreen—so environmental conditons can be expected to make a difference in catechin content. In fact one of the consequences of global climate change has been a decrease in spring rains with the development of droughts in both Yunnan and Fujian provinces, a problem for first flush leaves.**

Friend of Pairteas Selena Ahmed and her colleagues have documented the effects of the increase in spring droughts in Yunnan on catechin content and sensory qualties of the region’s teas.*** With drought and increased sun exposure, catechin content of the teas increased over the past several years, and local tea famers have noticed both a decrease in the sensory quality of the teas and a decrease in the price they recieve for their teas.

* Wang Chen, Lv Shidong, Wu Yuanshuang, Gao Xuemei, Li Jiangbing, Zhang Wenrui, Meng Qingxiong. Oolong tea made from tea plants from different locations in Yunnan and Fujian, China showed similar aroma but different taste characteristics.  SpringerPlus (2016) 5:576 DOI10.1186/s40064-016-2229-y.

**Chen Huo-Po, Sun Jian-Qi. Drought Response to Air Temperature Change over China on the Centennial Scale. Atmospheric and Oceanic Science Letters, 8(3): 113-119. 

***Ahmed S, Stepp JR, Orians C, Griffin T, Matyas C, Robbat A, et al. (2014) Effects of Extreme Climate Events on Tea (Camellia sinensis) Functional Quality Validate Indigenous Farmer Knowledge and Sensory Preferences in Tropical China. PLoS ONE 9(10): e109126.'

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