US League of Tea Growers and the aromas of tea

So excited about giving a talk via Skype about the development of tea aromas to the members of the US League of Tea Growers at their annual meeting in Mississippi. 

They will be hosted by Friend of Pairteas Jason McDonald of The Great Mississippi Tea Company. (Incidentally, their green tea won a silver medal among USA-grown teas at the Global Tea Championship last year, with a score of 93% in blind tasting!)

My talk will center around the aromas in teas and the processes by which they come into the cup. I'll emphasize time, temperature, and especially handling of the leaves as important for the development of the most delicious aromas. Here's one of the slides I prepared for the talk:

This slide shows compounds that emerge early in the processing of the tea leaves, and contribute to green tea flavor.

When a leaf is damaged, its cells immediately release hexanals—they give us the aroma of new-mown grass.

As injury and stress continue, leaves produce the three compounds in red—jasmonates, abscissic acid, and salicylic acid.  

Among its many functions, abcissic acid closes the stomata—the little "mouths"—on the underside of leaves that slow down water loss. You can easily imagine that large amounts of this compound are produced in the withering room! 

Notably, abscissic acid is also the precursor for the formation of nerolidol, the aroma compound that is the hallmark of high quality oolongs. The more punishment tea leaves experience when being transformed into oolongs, the more nerolidol is formed.*

Linalool and geraniol are normally stored as glycosides in the plant cell's central vacuole, far away from the enzymes that break up the glycosides. When the cell is damaged, the glycosides leak out of the central vacuole, come into contact with the enzymes, and the delicious cool rose-like aromas of linalool and geraniol waft in the air.

As for salicylic acid, it is the precursor for methyl salicylate. It takes time and a lot of processing for the leaf to form methyl salicylate, so you won't find it in green tea, only black. It is one of the compounds that give black tea is rich sweetness.

As for the green border around ß-ionone? As you may have seen me mention before, I can't smell this compound, and neither can some 40% of people of European descent. Pity, because people who can smell it say it smells delightfully floral!

* Ying Zhou  et al. Formation of (E)-nerolidol in tea (Camellia sinensis) leaves exposed to multiple stresses during tea manufacturing. Food Chemistry 231 (2017) 78–86.

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