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May 12, 2021 4 min read

There are many factors that determine the quality of any beer that you make. From ingredients, to process; rituals to equipment - homebrewers will argue the impact of any of the variables except for the two sacred truths: cleanliness and fermentation temperatures. Cleanliness and sanitation are known to be important from the start, but fermentation temperature seems to be cast aside in the name of simplicity for many new brewers. This doesn't mean that everyone should go out and buy the biggest glycol chiller they can but it does mean that temperature control should be top of mind for every brew. Plan for it, do what you can, and make sure we are getting the best possible result with what you are able to do. 

Why is fermentation temperature so important? 

Yeast are not a lot different than you and I in some ways. The two most fundamental needs we share are the need for food and comfortable living environment. We have to think of your fermenting beer as both. We've given them the sugars in the wort to eat, now we need to give them a comfy environment where they can produce the best possible product. If yeasts are too hot, they will produce undesirable flavors and alcohols that are harsh and contribute to the severity of hangovers. Too cold, and you'll see longer fermentation times, stalled fermentations, under-attenuation, and off-flavors. Think of yeast like Goldilocks - they like things not too hot, not too cold - just right. 

What temperatures do yeast want?

Different yeasts prefer different temperature ranges. Most common ale yeasts prefer temperatures from 62F (17C) to around 72F (22C) as a general rule. Lager yeasts want colder temperatures - from 48F (9C) to 55F (13C). The new darling of the yeast world are the kveik yeasts - strains isolated from traditional farm cultures in Norway - that will ferment cleanly at temperatures from 77F (25C) up to 100F (38C)! This makes them perfect for Florida home brewers who may not have temperature control equipment they need for other types of yeast. Yeast labs and scientists are busy identifying new strains that are even more flexible and producing good beers over a range of non-traditional fermentation temperatures. 

How do I control fermentation temperatures? 

I've got good news. You have options thanks to industrious and creative homebrewers and a responsive homebrewing market. Start by applying the "Big Three Homebrewing Decision Factors" - budget, space, and time. We'll start with the easiest, cheapest, and quickest ways and finish with the more expensive and sophisticated options. 

  • A cool room - if you have a cellar or basement that stays cool this is the easiest thing that costs no money, takes no additional space or time. You'll want a space that can hold temperatures somewhere between 50-60F (10-16C) for most ales. Yeast will heat up your beer as it ferments so you need the room to be cooler than your target temperature range. 
  • The 'swamp cooler' method - Find a tub that will hold your fermentor and enough water to get even with the volume of beer or at least halfway up the sides, then wet and wrap a towel or t-shirt around the exposed part of the fermentor being mindful that the towel is in contact with the water. It will need to wick water up from the tub. Add frozen water bottles or reusable ice packs to bring the temperature down. Don't be tempted to just add ice cubes directly to the water - you want to use something that will release its cold slowly. You'll want to replace these a few times a day depending on the temperature of the room you're fermenting in. Have enough bottles or ice packs that you can always have some ready when you need to replace them. Point a fan at the fermentor and the power of evaporative cooling will help stabilize your temperatures. 
  • Fermentation chamber - Here's where we jump into equipment. You can build, retrofit, hack, or cobble together many different ways to cool a small space. The key is that it's well insulated and actively cooled. Automatic controls make this even easier and more consistent. Most home brewers jumping into chambers are using a chest freezer or refrigerator with an external temperature controller. The current range of temperature controllers, like this Anvil controller, are simply plug and play. You plug the controller into the wall and plug your freezer/refrigerator into the controller and set the temperatures. The controller's temperature probe goes into the chamber and maintains your set temperature. Many homebrewers, myself included, had the most significant jump in their beer quality when moving to automatic temperature control. If you have space for a large enough freezer you'll be able to do ferment multiple beers simultaneously.
  • Glycol Chiller - this is the most precise and most expensive way to control temperatures on the cold side of your brewery. It will require the addition of a glycol chiller and controls as well as fermenters that have chilling coils or jackets for the cold glycol to circulate through. These setups are excellent for tight fermentation controls, can maintain multiple fermenters at different temperatures, and will cold crash and lager. This is definitely a setup for serious hobbyists who are willing to invest in a durable setup that gives them more control and greater flexibility in their temperature management. Glycol chillers have been used in breweries for decades and remain the preferred way to control temperatures. The technology is reliable, proven, and effective. As interest grows, newer units in the home brewing market bring down the cost and deliver the performance home brewers want in smaller systems for less money. 

Home brewers are far too ingenious to be limited to this list, but most of the home brewers I've known or helped use one of these methods with success. There are MANY great DIY builds out there on forums and groups. Certainly if that is your thing, have at it, and please share your methods in the comments. There are other commercial solutions involving solid state cooling that are intriguing but they're relatively new. No matter how you get there, the important thing is to get the temperature "just right" to make your yeast happy and get the best beer they can make for you. 


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