Fermentation control is probably the most important aspect of brewing good beer. You can make incredible wort, but if you ferment it wrong it's not going to taste like you want it to. By properly controlling fermentation you're controlling the most important step, the transition from sweet wort to beer! Yeast are picky about their environment and they like different temperatures for different stages of their metabolic cycle. You want to initially encourage yeast growth, which is an aerobic process and it will claim any free oxygen in the beer which if left alone could oxidize the beer and give it that papery off-flavour no one is looking for. Next you want to encourage metabolism of the maltose ( sugars ) which generates Alcohol and Carbon Dioxide. Finally you want to encourage Flocculation, the process by which the yeast go into a suspended state and sink to the bottom of the Fermentation vessel, this allows you to rack clear beer into your conditioning vessel or serving vessel. For optimal beer you need optimal fermentation. My plan is to control the temperature of the wort at the source, with a temperature probe embedded in a stainless steel thermowell that sits right in the fermenting wort. This should allow for pretty exact temperature control. The Beaglebone Black will control two circuits, one for heating and one for cooling to chill and ramp temperatures as required.