With the coming of spring (and hotter days), fermentation temperature control is once again an important issue. As I mentioned previously in the Analyzing Mead Recipes post, whatever yeast you choose for your fermentation likely has an ideal temperature range. Some yeasts are better than others operating outside their temperature range, but in general, it is best to find the right temperature and stick there. At our household, winter provides an ideal temperature setting for fermentation, as we keep the house in the mid 60s. This is right in the middle of many mead yeasts ranges. Unfortunately in summer our house often climbs into the 80s, well above the temperature range of most yeast types. This requires creative action to manage your temperatures and maximize their flavor contributions. Here are a few common ways to accomplish this.

The Fermentation Fridge

If you are a member of the American Homebrewers Association (AHA), or frequent their website, you might have seen a recent article on a fastastic homebrew setup for controlling temperatures. Most may not be able to afford a setup this elaborate, but this is a good example of how refrigeration can be used to control temperatures. In an ideal world, at TBM we would be using a similar setup to control our fermentation temperatures. The only way to truly replicate a recipe is to control the temperature, and fermentation chambers are your best bet on a small scale (jacketed tanks with glycol coolers also work, but are a significant increase in setup cost and complexity).

To build a fermentation chamber, start with a simple chest freezer. When purchasing one, ensure that there is adequate space inside to handle the number of actively fermenting musts or worts that you will have at any given time. You will also need a temperature controller to maintain a constant temperature of the chamber. Chest freezers are meant to keep their contents below freezing, but meadmakers are going to want their temperatures between 50 and 75 depending on the yeast.

Many temperature controllers exist. Your more basic controllers only take the measurement of the chamber and ensure that the temperature stays lower than your threshold. More advanced controllers might include two temperature inputs, usually the temperature of the chamber and the temperature of the must or wort. Lastly, the most advanced controllers include a measurement of the ambient air outside your temperature chamber in addition to the temperature of the must and chamber. This provides the best control of the must temperature, as it can predict fluctuations in the external environment to predict the heat transfer of the system. As you can imagine, these controllers get more expensive as their capability increases. Choose the best setup for you starting out. You can always upgrade in the future if need be.

At a later date I will provide details of the buildout of a fermentation chamber for TBM, but I haven’t sprung for the supplies yet. But that doesn’t mean I can’t keep a must cool enough to keep yeast happy. The next two options are great for those on a budget who aren’t yet ready to spring for a fermentation chamber.

The Carboy in Ice Bucket Technique

One way to keep a fermentation cold is to place your carboy or fermenting bucket into a larger container that has cold water inside of it. Playing around with the additions of ice, you can control both how hot and cold your must can get depending on your house temperature. I find it best to use ice packs or frozen water bottles rather than ice directly. With straight ice additions, you may overflow your bucket with too many additions.

Start with a wider bucket or tray than your fermenter with an interior dimension at least six inches high, strong enough to withstand the weight of your full fermenter, and waterproof. The larger your tray, the better. The amount of cold water inside acts as a heat sink, absorbing the temperature rise from an active fermentation and providing a barrier to the warmer ambient temperature. Five gallon fermenters can easily weigh 60 pounds when you include the weight of the carboy/bucket and its ingredients, so strength of the system is key. You don’t want to go through all this effort only to have it break (and spilling everywhere) during your fermentation.

Place your fermenter inside the tray. Fill the tray as high as you are comfortable, enough to provide adequate contact area with the bottom of the fermenter. Be sure to leave some room for ice pack additions. If you know the ambient temperature is above your ideal fermentation range, go ahead and add an ice pack to the tray. After 30 minutes, come back to measure the temperature of both the tray water and your must. If the temperature is still too high, add another ice pack. If it is in a good spot, or slightly lower, let it be. Check back a few times each day and add new ice packs when the temperature is too high, or remove old ones that are no longer cold. Over time you will get a feel for what is needed to keep your system in a good temperature range.

The Wet Rag Technique

The simplest, and possibly cheapest, solution to keep your fermentation cool is to drape a damp rag (or towel, or old t-shirt) around your fermenter and place a fan blowing in its direction. Tie the rag around the top of the fermenter to ensure it stays in place. Also try to blanket the entire fermenter, and not just a small portion of it, for the best results.

The evaporation of the damp rag will cool down your must, just like evaporating sweat helps cool you down. When you first start out doing this, make sure to check on it frequently to ensure the rag stays damp and that you don’t have the fan turned on higher than necessary (hey, there’s no reason to waste electricity if you don’t have to). You may have to swap the rag a few times a day to maintain a good temperature.

Well there you have it. Three options for maintaining an appropriate fermentation temperature, the fermentation fridge, the fermenter in ice bucket, and the wet rag technique. Do you have any other ideas for controlling your fermentation temperature? Let us know in the comments section below. Thanks for reading!