Converting a fridge for fermenting beer

Step 6 Adding a temperature controller

The easiest method of controlling the temperature is to buy an external programable thermostat.   If the fridge has a thermostat, you will want to set it to it's coldest settings so that the external thermostat controls everything. 

I use a digital Ranco controller, which works great, but is only single stage, meaning that it can control either heating or cooling, but not both at the same time.  It rarely gets super hot during the day and then super cold the same night here, so it hasn't been much of an issue.  The thermal mass of 15-20 gallons of beer is usually enough to even out most fluctuations.  The nice thing about it is that is's essentially plug and play.  I may replace it with a dual stage controller like I have on my kegerator, which will require a little wiring, but should make operation a little more convenient. 

In either case, it's a good idea to tape the temperature probe to the fermenter, so that the sensor is reading the beer temperature instead of the ambient air temperature inside of the fridge.  It also helps to tape a piece of foam or other insulation on top of the sensor.  If the probe is water proof, it can also be permanently mounted in a small vessel filled with liquid instead of attatching it to the fermenter.