The main water-soluble components of gyokuro are theanine (an amino acid), caffeine, tannin and vitamin C. Theanine is the source of the tea’s flavor, caffeine the source of its bitterness, and tannin the source of its astringency. Compared with sencha, the shade-cultivated gyokuro tends to be smoother, more full-bodied, and less astringent.
In particular, gyokuro is much richer in umami – a smooth, slightly sweet characteristic that is common to fine Japanese cuisine. It is this umami that is responsible for the full-bodied mellow sweetness of gyokuro. And it is the high content of theanine, an amino acid found in Japanese green tea, that is responsible for this abundance of umami.
So, why is gyokuro so rich in theanine? The answer lies with the cultivation process. Unlike sencha which is grown in full sunlight, gyokuro leaves are shaded from the sun for about 20 days just prior to being picked. During this period, the rate of photosynthesis becomes significantly reduced, and less of the theanine gets converted to other compounds.
In addition to the high theanine content, gyokuro also has a relatively high caffeine content. This is because gyokuro leaves include an abundance of tips and young shoots. However, thanks to the calming effect of the theanine, the overall effect of the caffeine is said to be gentler and more gradual than that of coffee.
For more information about the components of gyokuro, please visit our Components page.