The pumidor experiment continues and I’ve been learning plenty in the process, as expected. Wanting to stay on top of any potential for mold mischief I did a thorough check of all the cakes in mid December, two months of time in the cabinet, opening the wrappers on the majority of them to check closely for any signs. The good news is that nearly all the cakes looked fantastic. Pristine, even. I took a ton of pictures, mostly for my own records. Seems silly to post them here, but I'll put up a few for the visuals.
|"worry spot" circled, 1993 cake|
For the most part, there were no serious issues with regard to controlled humidity storage. But there were a few red flags present on a couple of cakes. Among the oldest cakes there were two that seemed to show very tiny areas of a bit of white frosting. Keep in mind that I was examining these with a bright light and a magnifying glass (in full anal-retentive mode, I admit). I took pictures of each of the worrisome areas and sent them off to several folks whose knowledge I trust. None could see in the photos what I saw with the magnifying glass. The photo pictured here is one such "worry spot" on a '93 cake. I've circled the area that had me concerned, but looking at it now I have a hard time seeing what had me alarmed. Still, it makes sense that it would be the older cakes, whose storage history is unknown, that would have the highest likelihood of developing mold issues. So this was lesson #1 – be the most cautious and conservative with the oldest cakes.
|2012 cake, mold developing on wrapper|
But down on the lowest shelf, on a few of the youngest cakes in my collection, there was a clear problem starting to develop. The three cakes were located in a stack of cakes setting closest to the humidifier unit. All were from the same vendor and had been wrapped in particularly thick paper. As I pulled them out to examine them I noticed that the knot of paper at the center of the underside of the cakes seemed actually damp (not hugely so, but noticeably so) and there were tiny spots of the very beginning of mold growth on and around the knot of paper. None of the other cakes in that stack (or anywhere else in the cabinet) had this same problem, only these three with the thick wrappers. Fortunately, the mold was only on the surface of the paper and hadn’t penetrated to the cakes inside. I’d caught it at the very earliest stages (lesson #2 – check your cakes EARLY and OFTEN if you’re adding humidity). But this was clearly a worrisome sign so I decided to open the doors to the cabinet to let the tea dry out for a period of time. I also removed the wrappers from these three cakes and replaced them with new wrappers.
|same 2012 cake pictured above, wrapper removed|
The small room where the pumidor cabinet is located is particularly warm due to the way the house was designed. It’s consistently about 10 degrees warmer than the rest of the house. While the cakes were sitting open to the dry air I placed a hygrometer in the room to check on the humidity levels. Without the humidifiers going and with the high heat of the room, the RH level was dry—REALLY dry--averaging between 30-35%. The longer the cakes sat out in this very dry air, the more anxious I was to get them back in the cabinet and get the humidity levels bumped up again. In total, they sat in the dry air for 4 weeks. I put them back into controlled humidity in mid January.
This time around I did a few things differently. First, I shuffled the cakes in the cabinet, placing them into different spots than they were before. Next, I placed five small (calibrated) hygrometers in different places throughout the cabinet. Over the next week I took readings from each of the hygrometers at various times throughout the day. It turns out the humidity levels are highest, and the temperatures lowest, in the lower part of the cabinet (graph below). You might be thinking “Well, duh!” but when I contacted the maker of the three cakes that had mold on the wrappers he did a similar comparison of hygrometer readings in his own storage and found the opposite to be true. Which leads to lesson #3 – never assume anything. It just further emphasizes the importance of getting to know your own storage conditions. There are no shortcuts or one-size-fits-all. If you’re experimenting with controlled humidity then GET SOME HYGROMETERS (they’re cheap) and check out different areas of your storage.
There's the whole matter of dew point, as well. I’m learning it’s not as simple as “dew point X is good, dew point Y is bad.” While I’m still far from understanding it all I’m currently spending a lot of time at this website, paying particular attention to the MOLD RISK factor. While I’m sure there are more things than just RH and temperature that encourage mold growth (airflow, the type of mold spores present), it’s a pretty good start at getting one’s head around what happens when you start playing with temperature and humidity. I sat down and charted the points from the hygrometer readings on each shelf, below. The blue circle on the left shows the general area of the readings from the top shelf, the middle green circle shows readings from the middle shelf, and the red circle on the right from the lowest shelf, with the mold risk parameters (as defined by the dew point calculator, linked above) enclosed on the right by the darker red sideways "V" shape.
What’s interesting is that I’ve got the set-point on my humidifier unit set at 60%, and yet the RH levels in the chart above show a range of 60-71%. So why am I getting such high RH readings? I think I know the answer. The regulating unit for the humidifiers is placed at the upper right corner of the cabinet, just inside the door opening which (thanks to the info gleaned from the hygrometer readings) is likely the driest spot in the cabinet. Fortunately this is an easy fix. I just need to factor in the average RH difference when calculating the set-point for the humidifier unit.
As for the inconsistency of RH levels between shelves and the pooling of humidified air in the lowest part of the cabinet, that’s a little trickier. Clearly it’s an airflow issue, but there are different ways to address it and I need to figure out which way is best. The humidifier unit has two sets of fans. The first set is located on the top of each humidifier. Whenever the regulator signals that the RH is low it causes the fans on the humidifier units to switch on, blowing humidified air straight upward (this is also why I have no cakes directly above the units on any of the shelves). The second set of fans (two small fans like the kind you’d find in a desktop computer) are placed at the top of the cabinet along the back wall and run as auxiliary components to the unit, with their own set-point for turning on and off that has nothing to do with the RH levels. For the data points in the graph above they were set to go off for one minute in duration every 20 minutes. I’ve changed them now to go off every 10 minutes and am hoping this will help to balance the hygrometer readings. Time will tell. I may have to set them to go off even more, or I might have to place them in different areas of the cabinet. There’s also the option of adding a few more computer fans to the two that are already hooked up. I’m also giving some thought to the general density and arrangement of the cakes on the shelves as this could also contribute to or impede air flow. This issue will probably require trying out different approaches to discover the best solution. I'll keep you posted!
This is all a great deal of fussiness, I know. But I find great fun in experiments like these, and most importantly I really love what the added humidity is doing to the taste of my teas! :)