Young Sheng Puer Storage Experiment: 36C vs 40C Temperature Comparison (3 month results)

This experiment, which began on March 1, 2019, should fulfill two purposes. First and foremost, to verify that my hotboxes will not cause defects to the tea. The second purpose, of much lesser importance this early on, is to note differences between young sheng puer stored at 36C and 40C.

Introduction & Context

A few months ago, I ruined a number of cakes of tea in both of my hotboxes, which were set to 40C. This was because of excess heat: My temperature sensor was placed too far from the heat source, meaning that the tea closest to the heat source was overheated. These teas were heated to around 46-49C.

The damaged teas have a particular flavor and aroma that, at this point, I can easily identify the slightest traces of. So the natural next step with this issue is to compare 40C to a cooler temperature, in this case 36C, to see if it helps with the situation.

Now that the context has been explained, I will describe in detail the design of the experiment:

  • There are two samples of tea; each is a quarter chunk of 2018 Yunnan Sourcing Impression sheng puer. Cake cores were removed from samples to reduce sample variation.
  • Both samples were conditioned to 65% RH at ~21C using Boveda packs. The generated humidity of each sample was measured separately in close-fitting mylar bags using a calibrated analog hygrometer. Once I ensured that both samples reached equilibrium moisture content within the mylars, I removed the Boveda packs from the bags, then zip-sealed the bags and placed them in the corresponding hotboxes to begin the 90-day storage period.
  • Once the storage period was complete, I let the samples acclimate to my ambient room temperature overnight before evaluation.

So, on that note…


Brewing parameters: 1g/15mL ratio. 6.33g leaf in 95mL gaiwan. Brewed at 208F using my custom water recipe. The samples for brewing were almost entirely unbroken leaf from the loosely-compressed rim area of the cake chunks.

36C Sample

Rinse: Surprisingly palatable. Reasonable amount of sweetness, no bitterness, no drying mouthfeel. Only a hint of that dustiness one would usually expect in a rinse. Pristine.

  1. Just slightly starting to open up. Nothing off is jumping out at me.
  2. The color is turning to a light yellow. Just a touch of sourness in the aftertaste.
  3. Golden color, identical in appearance to 40C cup #2. Low amount of mouth-puckering. A more pronounced sourness. Taking a whiff of the leaves still hot in the gaiwan, there isn’t a trace of sourness to be found. A great sign in this context. Not much bitterness. Astringency gradually building as expected. Not as good as the last cup, probably because I had to take a 10-minute break in between cups.
  4. Better, though still not especially pleasing. There’s nothing “wrong” with it, it’s just not a superb tea. Anyway, we’re only here to examine the effects of heated storage. And so far, it’s as good as I could’ve hoped. The aroma is quite nice, by the way. My teeth are starting to feel a bit sensitive.
  5. If I were describing a pair of headphones, I would say that the soundstage of the 36C pair is narrower than that of the 40C pair.
  6. Easily enough potency to continue to demonstrate differences in comparison to the 40C sample, but I get the idea. No need to continue, 40C wins hands down.

40C Sample

Rinse: Exactly the same as the 36C sample, except with a slight prickly sensation at the tip of the tongue.

  1. Unexpectedly, this cup has a slightly softer mouthfeel than the 36C sample. This difference is small but easily discernible. None of that unwanted prickly sensation from the rinse remains.
  2. The color is more of a golden yellow compared to the 36C sample. Once again, a smoothed out, fuller mouthfeel. A touch sweeter, allowing me to enjoy bigger gulps of tea. Whether or not there is a detectable sourness is hard to say. What I can say, though, is that there’s a proper balance of satisfying flavor, and no defects jump out at me.
  3. Proper golden color. Just a touch of bitterness. Astringency is starting to build. Not as good as the last cup, probably because I had to take a 10-minute break in between cups.
  4. Unequivocally better than 36C cup 4. There is simply more sweetness.
  5. By this point, the colors of the brewed tea are matching very closely. Neither sample is producing a darker or lighter brew. This cup has a hint of sourness, very slight. It is overall still more pleasant than 36C cup 5.
  6. Easily enough potency to continue to demonstrate differences in comparison to the 36C sample, but I get the idea. No need to continue, 40C wins hands down.

Conclusion: Both samples were free of defects after the 90-day heated storage period. The 40C sample tasted significantly better to me, as it had less sourness, more sweetness, and a nicer mouthfeel.

July 26, 2020 Update: Upon checking on the 40C sample, I noticed that it had been affected by heat damage. This experiment is now over.

September 4 Update: It turns out the 40C sample was not necessarily damaged, but affected by the lemon ester note; see this post for more information. This experiment will be superseded by others.

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