Why do we use different temperature water for different teas? (Tea chemistry)
Hello fellow tea drinkers.
I have been digging around the internet to try and find a complete answer to this question but really cant find anything past “because green and whites are delicate” and or “because higher temps extract more bitter compounds (caffeine, polyphenols).”
The effect water temperature has on the rate of diffusion of water soluble chemical compounds makes sense, but I don’t think that really answers the question of how does oxidation affect steeping. So what does the oxidation process do to cause a lesser oxidized tea leaf (white tea) to warrant lower temperature water and a more oxidized tea leaf (black tea) to warrant a higher water temperature? Are lesser oxidized tea leaves more permeable than higher oxidized tea leaves?
What do you think?
I really don’t know the answer but since it’s such an interesting question I’ll ramble on a little, take a guess. I would think the second idea listed as a standard answer does apply to green teas, that cooler water doesn’t extract the same bitter compounds but still does extract flavors well. Per my understanding bitterness and astringency aren’t the same thing, and it’s really the latter that is a concern, but I can’t tie it back to the names of related compounds anyway.
White tea doesn’t work as a great example for trying to potentially tie temperature directly to oxidation level because white tea refers to a group by processing type, not oxidation level, and those can vary. Most are in the middle, far below black teas in oxidation level, and probably more oxidized than less oxidized oolongs (greener TKY, for example). Even within the range of oolongs that mapping doesn’t seem to work since there isn’t so much divide between lighter and darker oolong recommendations. Of course any temperature recommendations can vary; I just heard someone that’s not so new to tea recommend brewing black teas well off boiling point, so in about the same range, although of course that varies too.
So I think it’s back to how fast different types of compounds extract, and at what temperatures, probably not so related to a general permeability of the leaves themselves, more about how those individual compounds react. This might be a good place to mention I’m not a chemist or food scientists, a completely unrelated type of engineer, so I’d have no idea. As an aside, optimums may not be as clear as they seem at first, more related to preference, since in Vietnam they like tea more astringent so they use hot water for brewing green tea, typically coupled with not limiting infusion contact times, just letting it go.
It is true that you sometimes extract less bitterness with a lower temperature. It also extracts less caffeine and less in general.
Could you explain more of your understanding about the whole tea category vs oxidation level concept? I am under the impression that it’s a straight spectrum from white, green, yellow, oolong, black, in that order. Is that not correct?
I do know higher oxidized teas have less catechins (which are Polyphenols, which have a bitter taste) because it is the oxidation of the catechins that turns a raw tea leaf into a black tea. So that means that brewing a higher oxidized tea at a higher temp won’t result in bitterness, not because they are less delicate but rather they just don’t contain the ability to become bitter. However, a CTC Assam black tea can still get super bitter. On the other hand, since green teas do still have much of their catechins, brewing at a high temp will result in bitterness.
I’m not the right person to explain why green tea and black teas can both be bitter (astringent, really, bitterness is a taste, picked up by receptors in the tongue versus flavors carried to the nasal passages, and astringency is a different thing, a feeling response to the tea also located in the mouth). I’m guessing different compounds are related but somehow even though tea research is a hobby that’s never been of particular interest to me, yet. Cultivars, plant types, processing variations and tea types, and most recently pu’er storage; those have been.
Explaining oxidation versus tea type is just basics, so easy to say a little. The types by oxidation range really only directly maps to green, oolong, and black types, with a general structure of green teas covering 0% to 10% oxidized, black teas above 80 or 90%, and oolong in the middle (but that gets cited differently, just close to that). Again white tea relates to a simpler processing sequence, not oxidation level, so the range of oxidation varies, typically somewhere in the oolong range though. Yellow tea includes something like a wet piling step, turning out a lot like white tea, but different. At a guess those will typically be oxidized similarly to lighter oolongs but the effect will be completely different (but I’ve only tried one yellow tea, and perhaps not a “typical” one since it was from South Korea instead of China).
Oolong can be complicated because they’re typically both mid-level oxidized and roasted, and roasting effects can be hard to distinguish from oxidation, in some cases. Dark roasted Tie Kuan Yin can be lightly oxidized but dark roasted, and Dong Ding style perhaps more middle-middle. Per my understanding—not an industry norm, just a loose convention—both Wuyi Yancha oolongs and Dan Cong are typically oxidized to a similar relatively moderate level, with the former varying across a range of roasting styles, light to quite dark, and the latter typically lightly roasted. But all that varies by producer, with slight shifts making up the range of styles those come in.
CTC teas being bitter (again astringent, really) relates to compounds coming in contact with the water that ordinarily wouldn’t, at least as much, in whole leaf versions. Now we just need someone into discussing compounds in teas to fill in some gaps, or sites like World of Tea typically do a good job with that.
Well, and to further what you were saying about preference, I have read a lot of people saying that they steep young sheng at around 200 degrees F, and in my mind there is not a huge difference between young sheng and pan-fired green tea.
Less oxidized leaves are often appreciated for the delicate flavors and aroma, which can easily be lost when steeped at too high temperatures.
Okay, so there are a few things in-play here. What we call “tannins”, are the polyphenol groups in tea; these include catechins, and theaflavin and other thearubigins. In green and unoxidized teas, whole catechins are the primary source of bitterness in tea. But in black and partially oxidized teas, catechins break down into theaflavin and other thearubigins.
Besides caffeine, theaflavin is the large contributor to bitterness in black tea (or “brightness”, and also causes the yellow colouring). The “accepted” ratio of theaflavin to other thearubigins in black tea is about 1:10 to 1:12 depending on the style/area/factory. Theaflavin is produced early in the chemical withering stage of tea, and peaks before tappering off much quicker than thearubigins, leading to dull teas if left unchecked. Other thearubigins start forming much slower, and contribute to the red colour seen in darker black teas and into post-fermented teas (which are quote low in TF; you can see why).
The fast-forming nature of TF is important to keep in mind when considering Darjeeling FF, which are not as wholly oxidized as other black teas. They contain a much lower ratio of TF:TR, with lower TR (and only a slightly lower TF) when compared to Assam-made teas, as well as a much higher total unfermented catechin count (owing likely to Darjeeling’s very ‘green’ style of making).
I don’t know the relative solubility potential of TF, but you can see where I’m going with temperatures/steep times when compared to catechins as a ‘bittering’ agent. I did have another paper that briefly studied the TF:TR ratios among a series of different production types and areas, but for some reason I didn’t save it and am now having trouble accessing it again. Ahwell.
CTC tea’s bitterness comes about from roughly three things: it’s increased surface area allows faster release of compounds into solution, it’s production (alongside other maceration-type unorthodox tea distortion) allows for higher levels of both TF and TR in the finished product, and it’s shorter wither setup results in a higher level of unfermented catechins (although this’ been eliminated for the most part; this affects more obsolete unorthodox production methods like legg-cut which undergoes no withering).
You can also consider var. sinensis versus var. assamica as another possibility, although. I can’t think of any papers that studied that off the top of my head, but the one on regional TF-TR variations mentioned earlier would be a solid starting point. Also interesting to note, on the side of Assam tea bitterness (on top of its use of the assamica varietal, which has a good track-record of being quite strong and sometimes bitter if you look at the regions), is that Assam teas only undergo ‘light’ withering, when compared to regions like Sri Lanka which hard-wither their teas before rolling (these result in different pre-rolling moisture contents,but also different timeframes for TF to peak and fall off).
Very good description but I think there is a shorter answer, certain teas especially greens taste better with lower temperature water.
“Certain teas” is what I was getting at—green teas’ bittering agents are caffeine and catechins, which aren’t present in black teas (with the exception of FF Darjeelings). It’s likely that catechins benefit from the lower steeping temperature/time.
But in black tea, theaflavin is the main bitterant (besides caffeine), and is a derivative of catechins. Theaflavin concentrations also different wildly between different black teas (depending on production technique and probably varietal), and are correlated to the concentration of thearubigan.
Because different tea types have different “major” constituents, this likely leads to them benefiting from different steeping parameters, based on the solubilities of each individual molecule (which also changes with temperature!), and our own personal tastes.
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