Jasmine tea, fake and real…

Have been exploring a fine paper in the journal Food Chemistry by Li-Fei Wang and colleagues that characterizes the aroma chemicals in tea through solid-phase microextraction–gas chromatograph (SPME–GC).*

True high quality jasmine tea is made through a laborious process in which jasmine flowers come into contact with green tea multiple times. Each time, the used flowers are removed, the tea is allowed to dry down, and fresh flowers are added back. In the process the tea/flower pile can reach temperatures as high as 40-48º C, as chemicals in the flowers and tea together undergo metabolic transformations and exchange of volatiles.

A major transformation is the loss of the typical green tea compounds that impart a grassy green flavor. These include 2-methyl butanal, 1-penten-3-ol, and 2-penten-1-ol, and especially n-hexanal. The only major “green” compound left is cis-3-hexenol, which has a fresh, fruity green aroma. At the same time the amount of volatiles that bind to warm and hot receptors increases. Two compounds that smell of jasmine, linalool and benzyl acetate, are relatively increased as well. Further, compounds such as methyl jasmonate are formed in response to stress, which add to the flowery aroma. At the same time, the treatment increases oxidation of the tea so that the result is a tea that resembles an oolong or even a black tea.

Fake jasmine tea is spiked with jasmine chemicals in order to give a jasmine odor. It may smell of jasmine but the jasmine flavor is faint or absent in the brewed tea.

The reason is that “green” chemicals remain in fake jasmine tea after treatment, because no metabolism occurs. These chemicals turn on the cool/cold receptors and turn off the warm receptors to which most jasmine-related compounds, with the exception of linalool, bind. At the same time, these jasmine compounds try to turn off the cool/cold receptors. The net effect is a tea that smells of jasmine but tastes like a weak green tea. 

Here are chromatograms from this paper that show the differences among green, true jasmine, and fake jasmine teas. The peak just to the right of the green line is cis-3-hexenol.

• The top chromatogram is from green tea. The peaks to the left of the green line correspond chiefly to the “green” compounds in the tea, which bind to cool/cold receptors.
• The middle chromatogram shows the peaks in true jasmine tea. The peaks to the left of the green line are tiny, while the peaks to the right are much higher. These peaks correspond to jasmine aromas and flavors, and to the tea compounds from leaves with a higher degree of oxidation, akin to oolong or even black teas.
• The bottom chromatogram corresponds to a fake jasmine tea. Many green tea peaks remain, and the peaks to the right of the chromatogram are much diminished in size relative to the ones in the true jasmine tea.

…that’s why the receptors in your mouth will know it when they meet a fake jasmine tea, even when your nose may be fooled!

* Li-Fei Wang, Joo-Yeon Lee, Jin-Oh Chung, Joo-Hyun Baik, Sung So, Seung-Kook Park. Discrimination of teas with different degrees of fermentation by SPME–GC analysis of the characteristic volatile flavour compounds. Food Chemistry. Volume 109, Issue 1, 1 July 2008, pages 196–206.