Ask Mr. Wizard

Heating Up A Fermenter


Luiz-Roberto Reboucas — São Paulo, Brazil asks,

Living in southeast Brazil (São Paulo State) I enjoy nice temperatures during the entire year. It ranges from 10 °C (50 °F) in the night during severe winters to 35 °C (95 °F) in the hottest summer. Being a homebrewer brewing 20-L (5.25-gal.) batches, I took over an old chest freezer and adapted it to accommodate my plastic conical fermenter (21-L/5.5-gal. capacity). The fermenter has an appropriate port for a temperature probe, and I use this information to control my chest freezer temperature. This normally poses no problems with lagers. However, when brewing ales in the wintertime, it is sometimes difficult to stabilize the temperature during the night; for example, required fermentation temperature is 20 °C (68 °F) and at night the temperature goes down to 12 °C (54 °F). The chest refrigerator´s insulation helps a little and the temperature only drops down to ~16 °C (61 °F). What should I do?


It’s always exciting to see questions coming in from around the world and realizing how homebrewing communication has truly become global. I assume that you have your chest freezer located somewhere without heating, explaining your concern about the cool temperatures at night. The easiest thing to do may be to simply locate your ale fermentations inside your house during the cooler parts of the year. If your fermenting beer does not drop below about 63 °F (17 °C) during the coolest part of the day, most ale strains will ferment to completion without a problem.

Another, and less approximate solution, is to use a secondary controller that can be used either for heating control or cooling control. When you want to prevent your fermentations from becoming too warm, the controller can be used to turn your freezer on and off, like you are currently doing. A two-channel controller will switch on a heat source when set for use as a heater. There are an assortment of heating blankets, pads, and lights that can be used in this application. Whatever you choose, make sure you carefully consider the safety of your plan. And if you use a heat lamp, make sure to shield your fermenter from the light to prevent damage from UV light.

Increasing the insulation thickness of your chest freezer is yet another option. Depending on the size and shape of the chest, it may be easy to add some insulation panels to the sides and top, either internally or externally. Controlling fermentation temperature is one of the best ways to improve homebrewed beer quality and you have a few options to improve what you have. Cheers!

Response by Ashton Lewis.