Expert: James Yee - 8/8/2008

Question
I recently purchased a Thompson humidor that holds about 50 cigars.  It has two humidifiers which, unfortunately to get started, I soaked in spring water (I now have distilled water so I will  continue to use this in the future).  After about 4 weeks, the humidifiers and the 2 drawers they are in became cover in mold. I did not notice the problem at first as it developed on the underside of them.  I've read how to get rid of it, but I am curious as to how it came about.  The humidity level has held steady at %70 after the first few days during which it was rising to that level.  The temperature in the room it is kept varies between 68 degrees (Fahrenheit) and 75, and there is no direct sunlight on the unit.  Any advice?

Answer
Hi Tom,

The first thing you should do is check to make sure that your hygrometer is calibrated and accurate.  If a hygrometer is not accurate and providing a false reading, mold can easily form when we're not expecting it.  Conduct a salt test on the hygrometer to ensure that it is accurate and working properly.

If your hygrometer is properly calibrated, then the mold may have formed from the spring water that was used prior to the distilled water.  Even though the humidor's humidity was/is consistent at 70%, bacteria in the water or pre-existing mold spores from a contaminated cigar can still flourish in a humid environment.  Mold can also come from contaminated fingerprints while handling the cigars/humidor. Mold is also more likely to form in tight, confining spaces inside your humidor where humidity cannot flow freely.  This is common in humidors that keep the humidification device(s) in compartments or drawers or is obstructed by trays, shelving or cigars themselves.  As a result, the humidity/moisture becomes localized in certain areas inside the humidor and cannot flow properly.  This will create mold.  Avoid obstructing your humidification devices with cigars and be sure to keep your humidifier(s) in a visible spot where the humidity can aerate freely.

Switching to 100% pure distilled water or bidest water (double-distilled water) will greatly reduce your chance of mold.  To prevent the humidification devices from inadvertantly creating too much humidity, you can also add either a pre-mixed 50/50 humidor solution to your humidification device or your own 50/50 mixture of distilled water and Propylene Glycol (the same key ingredient found in pre-mixed 50/50 solution.)  Mixing your own PG & distilled water is recommended because it will allow you to fine-tune the mixture so that it produces the humidity level that you desire.  (A 50/50 mixture should create 70% humidity but some people may prefer a slightly higher or lower humidity level.  This will require a custom mixture of PG and distilled water.)  

Propylene Glycol and pre-mixed humidor solutions are available at most cigar shops, drug stores and pharmacies.

Hope this answers your question. If you have any more questions, please feel free to just ask and I will be happy to help.

Regards,
James