Testing DPcalc.org’s Mold Predictions with Young Sheng Puer

The purpose of this experiment is to compare my observations of mold growth on young sheng puer to the predictions of dpcalc.org.

(This experiment was begun on the 7th of January, 2020.)

For this experiment I am using some 2018 Yunnan Sourcing Impression sheng that has equilibrated with my ambient relative humidity of ~50%. There are four 50g samples; each has been placed into a mylar bag. The humidity of each mylar bag will be controlled by a different Boveda pack: 65%, 69%, 72%, and 75% RH. All four bags will be resting at ~70-75 degrees Fahrenheit.

DPcalc.org’s predictions:

  • 65% RH – No mold risk
  • 69% RH – 232 days to mold (September 5)
  • 72% RH – 86 days to mold (April 12)
  • 75% RH – 38 days to mold (February 24)

I will be evaluating the results based on observed signs of mold and how close its occurrences are to the predicted dates. The results aren’t expected to be universally applicable.

Update: September 4, 2020 (241 day mark)

The sample stored at 75% RH has finally grown visible mold. The aroma of the leaf from the bag has been clearly off with minty notes for quite a while, but I wanted to wait for visible mold. Here are some of the affected leaves:

Excuse the subpar photography. As you can probably tell, most of the mold is growing on the stems, and I’m not sure what that indicates. Could it mean that stems have a higher water content relative to the leaves? Or that stems are simply an easier access point for the mold to reach moisture or other nutrients? Whatever the case may be, it does not seem feasible to store young sheng puer at a relative humidity as high as 75% at 70-75 degrees Fahrenheit in a sealed environment without encountering mold.

The remaining three samples at 65%, 69%, and 72% currently exhibit no signs of mold, neither in appearance nor aroma. I will continue to check on these samples periodically. If there is no mold on any of the remaining samples by the 1 year mark, I will feel confident in saying that 72% RH is a safe upper limit in the case of sealed storage at 70-75 degrees F.

Update: January 6, 2021 (365 day mark)

The remaining three samples still exhibit no signs of mold.


At a stable ambient temperature in the range of 70-75 degrees F, 72% relative humidity is a safe upper limit for storing young sheng puer in a sealed manner.

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