Proper Fermentation: Temperature Controller

Jamil Zainasheff, guru of all things homebrew, is oft qutoed as saying, “Proper fermentation is what sets apart great beers from just OK beers.” The first part of proper fermentation is using the right amount of yeast. The second part is temperature control. Fermentation temperature plays a crucial role in the final flavor of beer. Too cold and the yeast might not go. Too warm and off flavors are produced. Depending on the style, ingredients, and yeast, proper fermentation temperature ranges from about 45 to 85 F. Given this range, and the need to keep the beer at temperature for anywhere from 2-12 weeks, the only logical choice is to build a fermentation chamber.

In San Diego I’m generally not going to have a problem with my fermentation being too cold. Quite the opposite, without temperature control I have been limited to the upper range of beer temperatures; or about 1/3 of the known styles.

Even limiting my choices, I still ran into problems with temperature. Sometimes my beers were getting up to 78 F at the peak of activity. Ales that are fermented too warm will produce some weird flavors; fruity, spicy, sweet, and sometimes a sort of raw alcohol heat.

In my first half dozen batches of home brew I tried to make intelligent choices about the beer I was making. Beers that are heavy, hoppy, or fruity/spicy can tolerate a bit of the flavors produced by yeast. Stouts, porters, IPAs, and most Belgian styles are fine. Some Belgian beers even want high fermentation temps, so they can maximize the fruity and spicy notes in the beer. I was limiting myself to those beers, but then I wanted to brew a nice, lightly hopped, crisp American Pale Ale for the dog days of summer. That’s where I ran into trouble; my pale ale came out fruity and sweet. It tastes good, but its not what you want for that hot summer day.

Furthermore I realized there was a whole world of beers I was missing out on; wheat beers, crisp lagers, most german styles. Almost any beer with a strong malty character was off limits. So I recently bit the bullet and built a temperature controller. I say built, but really it was a matter of buying 2 critical elements; a freezer and a thermostat.

The freezer is a GE 7 cubic foot. I mention it not to plug the brand, but to cite it as an example with the proper dimensions to hold two standard carboys, side-by-side. The thermostat is a Johnson Controls digital temperature controller. The thermostat has a temperature probe that goes inside the freezer and an LED control panel on the front. The freezer plugs into the controller, which in turn switches power on and off according to the internal temperature of the chamber.

The tricky part of the whole operation is getting the temperature probe inside the freezer. The crude approach is to run it under the lid. This is problematic because it allows cold air to escape and eventually the magnetic seal strip becomes permanently distorted.

The slow-and-steady, and perhaps most common, approach is to build a collar for the freezer. The lid is removed, and a frame of 1×4’s is added to the top of the freezer. The lid is then mounted to the 1×4 frame and holes are drilled in the collar as desired. This solution is fail proof, but I fear also allows heat leaks into the freezer (since wood is not the best insulator). Furthermore, it seems like a lot of trouble.

The brute force method is drilling a hole through the freezer wall. This one’s tricky because the chiller coils are wound around inside the walls of the freezer. An ill-placed drill bit can nick a freon line or electrical wire and it’s game over for the freezer. In spite of the risks, I know several people who have successfully employed this method. They turn on the freezer with the lid open and feel for cool spots. There appears to be a 3-6 inch strip near the top that doesn’t get cold as fast as the rest of the freezer, maybe…

I had decided on the brute force method. I performed the open-lid test and identified a potential drill site in the top back, right next to the hinge. I was steadying my drill when Ms. FL came in and asked, “Why don’t you just run the wires through the drain?”

Why didn’t I?  I recall looking at another freezer model, where the inside drain hole and outside drain plug did not appear to lie in any kind of reasonable line. I guess after that I assigned all freezer drain systems to the ‘useles-to-me’ category. A closer look at my drain revealed it to be a mere 8 inches from the outside wall and in a direct path with the outside plug. Five minutes later, and I had a working temperature probe installed in my freezer, sans drilled out hole. Brilliant. I later added an old CPU fan and DC power supply and now I have convective cooling in my temperature chamber.

The first batch through was a witbier, a Belgian wheat ale with hints of coriander and orange. Of course the Second Law of Thermodynamics states that the Universe hates order (paraphrasing here). I have temperature control and I can brew any beer at any temperature. Of course now I’m setting up to brew 3 saisons; traditional Belgian “farmhouse” ales that are best brewed on the counter, at 85 degrees.


4 thoughts on “Proper Fermentation: Temperature Controller”

    1. The freezer was $210 at Home Depot, with free delivery. The temp controller was $75 at Austin Homebrew Supply; free shipping on orders over $100. The fan and power supply were scrap (free). So about $300. I tally all my costs and “savings” on beer. If I assume a 22 oz bottle of beer costs $7, I’m $400 ahead at the moment. When I stop buying gear the savings will really start to add up.

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