Before tackling Ruhlman's saucisson sec, I needed a place for the sausage to undergo curing for about 3 weeks at 50°F and at least 60% relative humidity (RH). My beer fridge usually only has a single keg in it and I decided to tweak this chamber a bit to see if I could achieve a steady temperature/RH.
Baseline for the beer fridge is 45°F and 30-35% RH. Too dry. I thought some water in the bottom might increase the humidity. It did, to about 40%. After a number of different substrates placed in the fridge failed, I thought about increasing the water temperature by using a variable temperature hot pot. It's not a trivial problem. The fridge has a thermostat, the hot pot at a higher temperature will cause an increase in the vapor pressure of the water resulting in a higher humidity and finally the interdependence of the temperature and relative humidity make this environment nearly impossible to predict or calculate outcomes.
Empiricism to the rescue. I was able to fine tune both the fridge setting and hot pot setting to achieve the following boundary conditions:
38-40°F/40%RH with the hot pot on lowest setting (off)
48-50°F/68-70%RH with the hot pot at 90°F.
Also, at 90°F, the water barely evaporates over the course of 24 hours.
I have to have that kind of flexibility because of what Andrew warned me of. When the fresh sausage goes in for a cure, it loses water over time, thus increasing the humidity inside the chamber. Consequently, I need to be able to decrease the humidity contributed by the water bath to maintain a constant interior RH as the sausage cures.
I have some long term monitoring to do to validate the setup, but I'm confident enough, and the sausage ingredients are inexpensive enough to take a stab at it. Andrew, I may take you up on your generosity of the sausage stuffer loan, I can't wait any longer.