And the Winner is…

Competition results

At a recent judging event, a GABA tea garnered first place in the oolong category beating out such well-established oolongs as a Roasted Jin Xuan and a Dahong Pao.[1] A great result for a GABA tea, but is something rotten in the state of tea classification? Should GABA teas, with their distinct flavor profiles be competing in the oolong category? We’ll get to that but first, what is GABA and what is GABA tea?




GABA, or gamma-aminobutyric acid, is found mostly in the brain where it functions as a neurotransmitter.[2] It is the most abundant of all neurotransmitters and it is thought by some researchers to counter the effects of cortisol, a steroid hormone that is produced by the body at times of stress.[3] In other words, GABA is reputed to have a relaxing, calming effect on the body.

There is debate, however, as to whether GABA, when taken orally as in tea, has any effect and some argue that it unable to cross the blood – brain barrier.[4] Importantly, however, GABA receptors have been found outside the brain in the liver and lining of the lungs.[5] This suggests that GABA may have effects even if it does not cross the blood – brain barrier.


Processing in an anaerobic environment. Image from

GABA tea is tea that contains elevated levels of available GABA. The teas are produced using a technique that was developed in 1987 by the Japanese researchers Tsushida Tojiro and Toshinobu Murai.[6] The key element in the process is that tea is not oxidized in the conventional manner but rather incubated in a sealed receptacle that contains only nitrogen.[7] But what is this transformation of the tea leaf to be called? I’ll follow Tojiro and Murai and refer to this process as “incubation.”

Tojiro and Murai conducted their research using shoots from the Yabukita cultivar. Following incubation under nitrogen the shoots were steamed for 1 minute and the amino acid levels calculated from a solution made by soaking the steamed leaves in water. The researchers found that the levels of GABA in the incubated leaves were significantly higher than those in a control group processed in an aerobic environment.

The Japanese government subsequently established a strict standard for teas if they were to be called “GABA tea.” These must contain at least 150 milligrams of GABA per 100 grams of tea. The teas are now produced regularly in Japan as “green” GABA tea and in Taiwan as “oolong” or “Jia Ye” GABA. There also are some “black” GABA teas produced in Taiwan.

The Flavor Profile

The Human Taste System
(source: Gordon M. Shepherd Nuerogastronomy)

GABA tea seems to be referred to as an oolong if the leaf has been bruised after withering and the tea finished in the familiar balled shape pioneered in Taiwan.[8] This “oolong GABA” has a distinct flavor profile that, after a bit of experience, is not overly difficult to identify.[9] Most notable is the forward fruitiness of the tea; some find guava and mango whereas others discern banana characteristics. This is accompanied by a slight sourness in the mouth and a soft finish.

There are, of course, notable variations among different GABA teas, but the point is that they do all exhibit a “family likeness” that is recognizable and that is recognizably different than that of oolong tea.[10]

Seven categories of tea

So, should GABA be classified as an oolong?

Tony Gebely has argued convincingly that tea is best classified by reference to its method of production.[11] From this perspective, GABA tea, with its unique method of incubation rather than conventional oxidation coupled with its distinct flavor profile, must be considered its own class of tea. GABA tea, no matter what it may look like physically, is fundamentally different than an oolong and cannot profitably be classified as one. I suggest, therefore, that there are at least 7 categories of tea: white, green, yellow, oolong, red (black), dark (heicha) and GABA.

I have no doubt that the GABA tea that won the oolong category in Toronto is anything but a very fine tea. It just isn’t an oolong and should not be judged as an oolong. This does a disservice to both categories.

That’s my view. What do you think?

[1] The Toronto Tea Festival, 2018.

[2] See “Anxiety Neurotransmitters” in The Brain From Top to Bottom

[3] See

[4] Most seem to conclude that, given a healthy blood – brain barrier, GABA molecules are too large to permeate this barrier. See For the opposite view see:

[5] See Erwin Sigel and Michael Steinmann “Structure, Function and Modulation of GABAA Receptors” Journal of Biological Chemistry downloaded from

[6] Tojiro Tsushida & Toshinobu Murai (1987) Conversion of Glutamic Acid to γ-Aminobutyric Acid in Tea Leaves under Anaerobic Conditions, Agricultural and Biological Chemistry, 51:11, 2865-2871, DOI: 10.1080/00021369.1987.10868498

[7] Ibid. The degree of conventional oxidation in tea is, from a chemical point of view, based upon the extent of catechin oxidation. This means that the catechins lose electrons and the tea leaf becomes “oxidized'”. Although this does happen in processing GABA tea, hence it is “oxidized” from a chemical perspective, there is no catechin content criterion for commercial GABA tea (TRES, private correspondence.) Hence my contention that the transformation of the leaf in GABA tea is not “conventional oxidation.” Further, Eric Scott has convincingly suggested that the correct term for oxidation in tea is “enzymatic browning”, “The science and nomenclature of tea processing Part 1: Enzymatic browning:” I thank him too for prodding me to make my use of the term “oxidation” clearer. It is my responsibility alone if I have not.

[8] This is not universal and some vendors refer to the tea as “green tea” because it is not oxidized. On the origins “ball shaped” tea see my earlier article “Getting the Ball Rolling” at:

[9] From this point onward, I restrict the argument to “oolong GABA” tea, although much the same could be said of “green GABA.”

[10] I do not mean to suggest that there is a “profile” into which all oolongs fit. The variation among different oolongs is marked.

[11] Yet he nonetheless includes GABA tea in the oolong category and makes no mention of “green” GABA. See Tony Gebely (2016) Tea: A User’s Guide Eggs and Toast Media, Chicago, Ch. 5 and p.108. Gebely does suggest seven categories of tea but his seventh is “altered tea” which, I think, cannot be sustained. See my review of the book at and my article “Black is Black, I Want My Oolong Back” at

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