In the last post I briefly discussed the benefits of a healthy fermentation—how it can help drive off unwanted bacteria and wild yeast and eliminate off flavors and aromas. As a reminder, the three basic aspects of a healthy fermentation are pitch rate, fermentation temperature, and fermentation time.

In this post I want to talk in detail about fermentation temperature. After pitching your yeast it may be tempting to throw the fermenter in a closet or in the corner of one of the rooms in your house and let the yeast do its thing. If you do this and your beer ends up good, congratulations! The closet or room you ferment in probably has a temperature that hangs around 68º F. What this method doesn’t take into account is added temperature from fermentation, the optimum temperature for the strain of yeast used, and the ability of the brewer to control yeast derived character by dialing in the fermentation temp.




Fermentation Temperature

When beer ferments, the molecular processes taking place between the yeast and sugars create enregy in the form of heat. Depending on the yeast strain, the process of fermentation can add up to ~5º F to the overall temperature of the fermenter. So, if the ambient temperature of the room you ferment in is 70º F, you could be fermenting at 75º F, causing the yeast to over-produce esters and phenols, which come across as off-flavors. Warm fermentation also tends to muddy a beers character and drive off any late hop character added to the beer. Odds are the beer will be drinkable, but a high a fermentation temperature will generally not result in a good clean beer.

However, some yeasts react well to higher fermentation temperature, like Saison and Brett strains, while other yeasts prefer lower temps, like Kolsch and Hefeweizen strains. It is important to do a bit of research before you pitch and find out what the recommended temperature range is for the strain of yeast you are using. This information can be found on the manufacturer’s website.



Effects of Fermentation Temperature

Picking a fermentation temperature within the recommended range is a control point in the brewing process that many home brewers do not take advantage of. The general rule is that lower temps in the range will produce less yeast character, and higher temps in the range will produce more yeast character. For example, a Hefeweizen fermented with WLP300 has a recommended temp range from 68º–72º F. This beer will have more clove/bubblegum character if fermented at 72º and less if it was fermented at 68º. All the brewer has to do is decide what character they want for their beer and make sure the fermentation temperature will help achieve that character. Pretty simple.



Tips for Controlling Temperature

If you are interested in controlling fermentation temperature, there are a few ways to go about it. If your fermentation environment is too hot, you can place the fermenter in a tub of cool water, or place a damp towel over your fermentation vessel. If your environment is too cold, you can use a space heater to warm the ambient temp. or place a heating pad/heat wrap around the fermenter. Keep in mind that these methods aren’t exactly accurate, and constant monitoring and adjusting is necessary.

The best way to control fermentation temperature for home brewers is creating a fermentation chamber. I won’t go into the details of how these are created, but a quick Google search should provide you with all of the instructions you need. The basic idea is to create a chamber that is hooked up to a temperature controller so that the brewer can dial in the desired temperature and let the ferment go. These are a great option, but require space and can be costly to create.

Personally, I brew most of my beers in the cold months and ferment in my garage. I use a heat wrap hooked up to a temperature controller, which allows me to ferment my beer at any temperature above 40º F, which is great for almost all lagers and ales. During the summer months when ambient temp. in my house is ~75º F , I like to brew Saisons, since Saison yeast loves the mid 70’s and low 80’s.




We home brewers tend to be an inventive bunch, so figure out what works best for you. Just like brewing, there is no one right way to control fermentation temp. But remember, fermentation temp plays a huge role in the overall character of the beer, and paying attention to it could be the key to turning your good beer into great beer.



Up Next: Fermentation Time