Heated Storage System

This post details my personal heated storage system.

It’s just a modified version of Marco’s hotbox. As I ran into various issues throughout my time experimenting with it, I had to make some adjustments. These adjustments were: installing a second heat mat on the ceiling of the hotbox, placing the temperature sensor inside a mylar bag, and using bookends to position the cakes and keep them in place.

I tried installing a fan to improve the evenness of heat distribution, and it was an improvement to the single heat mat design, but using two heat mats worked much better in practice, with an average temperature differential of -0.5°C from the sensor’s reading.

Parts List


The black line is drawn over the temperature sensor, which is oriented horizontally, roughly at center of mass:

Try to replicate the environment of your cakes for your temperature sensor. Since the cakes are in mylar bags standing up, your sensor should be as well. Place the sensor inside a mylar bag and tape it (oriented horizontally) from inside. Place this mylar with the sensor in it in the center of the hotbox, with even amounts of tea on each side. The location of the sensor should be at center-of-mass.

This mylar bag holds the temperature sensor, and should be placed in the center of the box:

Keep the hotbox mostly full to improve temperature stability. Note that there’s also such thing as too full. This is a reasonable amount of tea to fit in the box:

Both mats plug into the outlet splitter, which plugs into the temperature control unit.

Best Practices

  • Pre-condition the tea at room temperature by throwing a Boveda pack and a cake of tea into a sealed mylar bag. Every couple of weeks, check the generated relative humidity by removing the Boveda pack and placing a calibrated hygrometer into the bag with the tea and sealing the bag for 4 hours. When the tea has reached your target humidity, make sure to remove the Boveda before placing the sealed bag into the hotbox. (Note: the time it takes to measure generated RH depends on the compression of the tea among other factors. Most loosely compressed tea cakes will get you an accurate reading in only 2 hours, but it’s better to wait extra just to be sure.)
  • Use bookends to position the mylar bags and keep them in place.
  • Rest any samples for 30 days at room temperature outside of the hotbox before any serious evaluation. Tea can suffer jet-lag after changes in temperature.
  • It’s advisable to spend the first 6-12 months of storage just storing samples of a diverse array of teas at various temperatures and humidity levels to get an idea of how each variable affects each tea. Work out the kinks in your setup before committing any full cakes.
  • For any serious length of uninterrupted storage, heat-seal your mylar bags. Even the best mylar bags I’ve found, linked in the Parts List above, can leak humidity, especially when heated.

Additional Thoughts

  • As heat evaporates moisture from the tea cakes in sealed mylar, the relative humidity increases a few percent. I’m currently working on generating some tables of data to demonstrate this, so for now refer to Marco’s post.
  • After roughly two years of heated storage experience, I have formed a preference for 30-32°C storage of puer pre-conditioned at room temperature to 60-65% RH.


  1. So from reading Mgualts experiment…he advised conditiong the cakes, then storing sealed with no humidity pack…is this the practice you follow? I’ve read some people seem to think leaving the packs in mylar with the cake any longer than it takes to condition the RH of the cake is inviting mold problems.


  2. What do you think about breaking up cakes for storage in this set-up (when space is not an issue)?
    Reason for question, a quicker transformation seems plausible.


    1. Good question, I sometimes break up cakes into quarters or halves to increase the number of possible sample sizes using the same amount of tea for some of my storage experiments. It can be done, but is only recommended in the context of testing different storage treatments on chunks of the same tea. I don’t advise breaking up cakes for aging purposes. Ideally, you want to maximize tea mass to improve the storage quality. Breaking up cakes will increase the amount of tea surface area, meaning faster aging technically, but storage quality can suffer as a result.


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