Fermentation Temperature Experiment

I consider fermentation to be the final frontier of homebrewing. Ingredients are pretty easy to pick out. Then you start worrying about things like quickly cooling your wort after brewing, but a wort chiller is a quick solution.

Once you go to all-grain, it’s mash temperatures and efficiency. You can even start to control the mineral content and pH of your water. That’s manageable.

Fermentation is probably the most impactful part of the process on the final character of the beer, yet it is the one part of the process that homebrewers often have the least control over.

I wanted to do an experiment to see how much difference fermentation temperature made on the beer. So I brewed 10 gallons of pale ale and split it into two five-gallon carboys. The original gravity was 1.064. For reference, the recipe is at the bottom of the post. I used nothing but malt, hops and yeast. No other additives.

I used the same yeast in each carboy: Wyeast 3522 Belgian Ardennes. One carboy was kept out at room temperature, around 68 degrees. The other went in my homemade cooler box along with a space heater set at 80 degrees.

The difference in the fermentation itself and the finished beer was remarkable. Temperature and had a much greater impact than I would have guessed. Here is the tale of two beers separated at birth.

The 68 Degree Fermentation

Primary fermentation finished in about 6 days. The final gravity I measured was 1.010, coming in at about 7.5% ABV.

The beer is a golden yellow with a frothy white head. The aroma is heavy with clove and spice. The flavor has cloves and dark fruit, like prunes or dates. It was very unexpected from such a lightly colored beer. That’s usually something I would expect from a dubbel or a darker Belgian.

The 80 Degree Fermentation

Primary for the 80 degree finished in about 3 days. It also finished drier than the 68 degree, at 1.006. (8.1% ABV). This isn’t unexpected, as warmer temperatures give the yeast more energy to work faster and harder.

The color is about the same as the 68 degree, but the head is much creamier with finely tight bubbles. The aroma and flavor is bright, with notes of bubble gum, banana and white pepper. It has a noticeably cleaner, drier finish than the 68 degree, which makes sense since its FG was a scant 1.006.

Like a parent choosing between their children, it’s hard for me to say which beer I like better. They are both good in their own way.

I had read about the importance of fermentation temperature in the production of esters and different character in beer, but I had no idea the effect would be this pronounced. These taste like two completely different beers, not born from the same wort. This will certainly be a part of brewing that I’ll pay more attention to going forward.

Untamed Belgian Pale Ale (10 gallons)

18 lbs Belgian Pils
2 lbs Belgian caravienne
1 lb Belgian aromatic

3.0 oz French Strisselspalt 2.9% AA (60 min)
3.0 oz French Strisselspalt (20 min)
1.0 oz French Strisselspalt (0 min)
4.0 oz French Strisselspalt (dry)

Wyeast 3522 Belgian Ardennes Yeast (4 packs)

OG: 1.064

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About Brian

I like beer.
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6 Responses to Fermentation Temperature Experiment

  1. EnglishPhil says:

    Very cool. This is precisely why it sucks to homebrew in the south! No basements (at least in Charleston) and no real means to viably maintain a low ambient temp without creating something. Being new to homebrewing I am quickly becoming aware of these issues. The video from my kit says that once the wort is created and the yeast is pitched that’s it! “Let the yeast do the heavy lifting” uhh they forget to mention that during the heat waves here in the south the house reaches 80 deg. To enjoy the beer in it’s intended fashion you must maintain the temp that is appropriate for your yeast. Most beers enjoy 70 deg and less… much less…

    I have to give a shout-out to my lovely wife for allowing me to utilize the spare bathroom to be the “Fermenting Chamber” if you will… I actually utilize a method called the “swamp bath” Basically putting the carboy in a Rubbermaid container filled with about 1″ of water and a T-shirt draped over the carboy. The idea is I can place as many frozen bottles of water I need to get the water the temp that I need and as the water evaporates it rises up the shirt thus cooling the beer during the fermenting stage. seems to work pretty well. I have kept my beer at a cool 66 deg while the house has been 77 or so.

    It is good to know that if the beer does reach a stage not intended for the yeast that not all is lost and its still beer and decent at that. :) Cheers!

    • Brian says:

      Though a pain, that’s a good method to keep your beer cold. as a new homebrewer, I commend you for taking that into account. Sounds like you need to be brewing Belgians and saisons!

  2. Eric Vernon says:

    This is a great post. Living in Minnesota I have the opposite problem as you. I enjoy Belgians in warm weather, however my basement stays a pretty steady 64-67 in the winter, so I have to lug a carboy up 3 flights of stairs to get it warm enough to heat up. If I brew them during the summer, they aren’t ready in time for me to enjoy them in the summer. Not being able to reliably control the temps, I always just accept that it is what it is. It’s nice to see that there really are some differences that can affect the temps, and it’s important to find ways to keep temps down or controlled to extract the flavors you want. I’ll have to play around with some methods of controlling my temps more.
    They sound delicious! Nice experiment!

  3. Wow, great experiment. Once I started respecting yeast, my beers started getting much better! I used to think yeast was a BEAST…but now I know that yeast is your friend that you want to make as happy as possible. I do a ton of experimenting, but haven’t done a split batch at two different temps yet. Sounds like a great experiment for 3711 this summer!

  4. Annette says:

    I appreciated reading your experiment. My husband and I, both engineers, brew here in San Diego with no basement…. We are getting ready to make a hefeweizen(for me =0 ) and we’re investigating how to control temp. Glad that others showed their tricks too!

  5. Dr.Oppotimus says:

    I live in NC were the summers are pretty toasty. My cure for getting temps lower was to put my fermentor next to an air conditioner vent (I have floor registers) and covered it with a box. I cut a 2 inch flap in the top of the box so I didn’t lose the vent to cool the room. That box over the vent works great! the temps are reading 61 on the thermometer stuck to the side of the fermentation bucket. While it’s not ideal lager temp (54 degrees for my Bock) it’s good enough for government work. I did an Irish Red in the middle of July and it came out awesome. I had to fight off the neighbors to keep them from drinking it all.

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