Sorry for my lack of posting over the last few weeks, but I have had the amazing opportunity to go to the UK for 10 weeks for research, and spent last week recovering from jet lag, learning English slang (like ‘having a nosey’) and setting myself up! Anywho, it’s QJART time!
Anyone who is a lover of tea, or has visited the tea shop T2, would recognise that different teas have different characteristic aromas, which depend on the leaf type and manufacturing process. But what makes up the smell of green tea?
A nice green tea in a green cup with a green teapot… So green, must be environmentally friendly! 😉
Three cultivars of Chinese green tea (Longjing, Maofeng, and Biluochun) were analysed by researchers in Japan to identify which volatile compounds make up the characteristic aroma of green teas. They began by first extracting the volatiles from the tea infusions, using a method called ‘SAFE’ (Solvent Assisted Flavour Evaporation).
The distillation unit used in SAFE is quite complex!
This method involves first the solvent extraction of the volatiles from the teas, followed by the use of a specialised glassware and high vacuum pump system to extract the tea volatiles from the solvent. The volatiles are then concentrated to give the SAFE extract, which can be used in gas chromatography-olfactory (GC-O) (an instrument which first separates the volatile components and then allows you to sniff these volatiles through an attached ‘nose’).
See that in front of her nose? That’s the ‘nose’ where you smell the separated volatiles!
To identify which volatiles contributed the most to the green tea aroma, the authors used Aroma Extract Dilution Analysis (AEDA). In AEDA, the SAFE extract is diluted a number of times, to give different Flavour Dilution (FD) factors. For example, diluting the original sample by four in solvent will give an FD of 4. Diluting again will give an FD of 16, and continuing on will give 64, 256, 1024, and so on, multiplying by four each time. The whole idea behind these dilutions is that the concentration of the individual components should become weaker and weaker with each dilution. Therefore, if we can still smell a particular volatile at the highest FD factors using GC-O, then it is associated with being a major component of the aroma.
Fifty eight odour-active peaks (separated volatile components which had a smell) were identified in the teas, at different concentrations in the different cultivars. Of these, seven had the highest FD factors in all tea cultivars, and are therefore believed essential for the aroma of Chinese green tea, including vanillin (smells like vanilla), geraniol (smells ‘green’), and (E)-isoeugenol (smells floral or spicy). The authors further suggested that (E)-isoeugenol, which was newly identified in Chinese green tea, was a product of the manufacturing process rather than the leaves themselves.
(E)-Isoeugenol smells floral or spicy, and is a volatile found in the aroma of green tea.
Next time you sit down with your cuppa, take in a deep breath through the nose, and admire those volatiles.
Baba R, Kumazawa K (2014) Characterization of the Potent Odorants Contributing to the Characteristic Aroma of Chinese Green Tea Infusions by Aromatic Extract Dilution Analysis. Journal of Agricultural and Food Chemistry 62: 8308-8313