L-Theanine

Definition

L-theanine (γ-glutamylethylamide) is the main free amino acid in the tea plant and is rare elsewhere in nature; it makes up roughly half of the free amino acids in tea leaves and typically 1-2% of dry leaf weight. It was identified in gyokuro in 1949 by Japanese researchers. Theanine is synthesized in the tea plant's roots and carried up to the young shoots. In sunlight, the leaf converts much of it into catechins, the polyphenols behind bitterness and astringency. Restricting light reverses the balance. That is the reason Japanese gyokuro, kabusecha and the tencha used for matcha are shaded for roughly one to four weeks before harvest (kabusecha at the short end, tencha at the long end): shading keeps theanine high and catechins lower, producing their sweet, brothy, umami flavor. Early spring harvests and young buds also contain more theanine than summer and older leaves. In the cup, theanine contributes the savory-sweet, mouth-coating quality called umami. It has been studied for its effect on alertness and relaxation, particularly in combination with caffeine; tea contains both, but findings at the amounts found in a cup of tea are modest, and no specific benefit should be expected from one serving.