A swamp cooler, or water bath, is one of the simplest and most effective ways to regulate fermentation temperature. Because of the excellent thermal conductivity properties of water the temperature of the fermentation tracks that of the water temperature within one degree. Fermentation temperature has a major impact on the flavor of the beer. Fermenting toward the high end of the yeasts range (65-75 for Ales) will add more characteristic phenols. Fermenting toward the lower end (60-65) will leave a more clean taste and can leave more residual sugar. Lagers are typically fermented even cooler at 45 to 55 degrees, and yet other yeasts are designed to work best at temperatures near 80 degrees.
Control of the fermentation temperature is therefore a wonderful tool to have on your homebrewing belt.
In a previous blog post using ice to ferment at low temperatures. In this post a method for fermenting at higher temperatures will be described in detail.
If you keep your swamp cooler in the basement the temperature of the water bath will likely be in the low sixties or below when no heat is added. If a way to add a temperature controlled amount of heat is introduced, fermentation at temperatures above the ambient air temperature are possible without any interaction during the fermentation processes. The easiest, and best way that I have discovered to do this is by using an aquarium heater.
When selecting a fish tank heater for your water bath there are several factors that you will want to evaluate. The heater you select needs to be effective for heating the volume of water in your swamp cooler. A 50W heater is good for 10-15 gallon fish tank, This is a reasonable size for keeping a 5 gallon batches of beer about 10 degrees above air temperature, but if you want a larger temperature difference you might consider a 100W heater. Next is temperature. Make sure to select an aquarium heater that has a thermostatic control, not just a heat adjustment knob. During the initial phases of fermentation the yeast will produce a fair amount of heat, and toward the end it will not be producing much heat at all. In order to maintain a constant temperature it is therefore important that the heater can regulate the amount of heat it adds to the tank based on the temperature of the water. Temperature range is also an important consideration. The fermentation temperature of yeast is close to that of a typical fish tank, but check that the heater has setting for the range you will be using.
After doing a lot of research and evaluating different products the best one I have found is the Fluval M Submersible Heater. The temperature is settable from 66 to 86 degrees which is perfect for ales. It also stretches into higher temperatures that many Sasion and Belgium yeasts prefer. The best part is that it is less than $20 at Amazon as I write this.
Today I popped open a bottle of a "Sasion Terri" that I made with the Fluval M 50W submersible Heater, and it't came out perfect! Without this heater I would have to wait until May of next year to try this!
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