Author: Marshall Schott

For the first fermentation temperature xBmt, I compared Schwarzbiers fermented up to 12°F apart using WLP029 German Ale/Kölsch yeast. Once it was revealed that a statistically significant portion of tasters were unable to distinguish between the 2 beers, I received numerous comments about the various factors that could have influenced these results– the yeast is too clean, the beer is too dark, the temp range wasn’t wide enough, warm fermented batch shouldn’t have been pitched cool. We had to start somewhere.

Truth is, with a variable like fermentation temperature, my plan all along has been to repeat this xBmt under different conditions using different yeasts in different recipes. In the weeks that followed publication of the first fermentation temp article, I paid close attention to the many recommendations I received for a follow-up xBmt, one of the most popular being to use a more characterful yeast with each batch pitched at their respective target fermentation temps. I also searched through some of my favorite homebrewing forums to discover the certainty with which some people claimed fermentation temp was key to making great beer– to be sure, my username was among those advocating for cool and controlled fermentations. Finally, I sought the opinions of a few dudes I regularly chat with and whose opinions I hold in high regard. The general consensus of this group was to use WLP002 English Ale Yeast and ferment it “no warmer than 72°F,” as a few reported experiencing intense ester formation around that temperature.

No warmer than 72°F, eh? Hah!

| PURPOSE |

The purpose of this xBmt is to investigate the qualitative differences of 2 beers made from the same wort, pitched with the same amount of the same yeast, and fermented at temperatures 10°F apart from each other.

| METHOD |

Of all the suggestions I received regarding recipe choice, there was about an even split between a low OG English Ale and a low-moderate OG Belgian Ale. Since I had been pining for a tasty English Mild, that’s what I went with, figuring the lower alcohol content might help to emphasize any differences between the batches. To those who wanted the Belgian beer, I promise I’ll get to it at some point.

English Mild Recipe

Batch Size Boil Time IBU SRM OG FG ABV 11 gal 60 min 21 12 1.039 1.013 3.4 %

Fermentables

Name Amount % Domestic 2-Row 12 lbs 80% Crystal 60 1 lbs 7% Victory Malt 1 lbs 7% Brown Malt 8 oz 3% Pale Chocolate 8 oz 3%

Hops

Name Amt/IBU Time Use Form Alpha % East Kent Goldings 28 g/~18.5 IBU First Wort Hop FWH Pellet 5.7% East Kent Goldings 21 g/2.5 IBU 20 min Boil Pellet 5.7%

Yeast

Name Lab Attenuation Ferm Temp WLP002 English Ale Yeast White Labs 67% 66°F & 76°F

A couple nights before brewing, I made a starter of WLP002, that quintessential chunkiness showing up within about 12 hours despite being a 5th gen harvested from prior starters.

I collected the entire volume of water and milled my grains the night before brewing, as I found this makes for a much smoother start to my early brew days. I was up around 5AM the following morning and mashed in about 20 minutes later. I was aiming for 153°F but duty called after I transferred the strike water to the MLT to pre-heat… the temp had dropped a little more than expected since I forgot to close the lid all the way. Whatever.

About 10 minutes into the mash, I found I nailed my target 5.2 pH as predicted by the Bru’n Water Spreadsheet, my preferred brewing water calculator.

After about an hour in the MLT, I filled my kettle with about 13 gallons of sweet wort, the FWH addition of EKG becoming immediately fragrant.

I cranked my burner to full blast, added a couple drops of FermCap-S to stave off a sticky boilover, then proceeded to clean my MLT. I added more EKG hops 40 minutes into the boil, waited another 20 minutes, then killed the heat and began to chill the wort.

Since my water is still cool enough to allow for chilling to my preferred ale fermentation temperature, I had to closely monitor the temp of the wort so as not to over-chill the half that would be fermented warm. My plan was to ferment the batches 10°F apart, this time pitching each at their target fermentation temps in order to account for any impact cooler pitch temps might have. For WLP002, I like to stick right around 66°F, which would mean the warm-fermented batch would be fermented at… gulp… 76°F!

That’s 8°F warmer than the top of the range recommended by White Labs. Shit. Outside of a couple Saisons, I’m pretty sure I’ve never let a beer get this warm during the first few days of fermentation. I chilled the rest of the wort, got it into a carboy, then placed each in separate fermentation chambers set to their respective temps.

Knowing that one of these beers was going to ferment so warm made me feel kinda funny. The large starter was split evenly and pitched. Signs of active fermentation began to show on the warm fermentation beer within just 4 hours.

At 24 hours after pitching the yeast, things were starting to pick up for the cool fermentation beer, from this point forward it looked similar to the warm fermented batch.

After 3 days of fermentation, both beers were showing signs of slowed activity. It was at this point I moved the cool fermentation carboy into the same chamber as the warm fermentation batch and turned the controller’s warming function off, allowing both to rest at ambient temperature, which was about 70°F at the time.

A hydrometer sample taken a couple days later revealed the warm and cool fermentation beers to be at 1.010 and 1.011, respectively.

After 3 more days and another hydrometer measurement that confirmed the first, I crashed the beers, fined with gelatin, and kegged them up. They were carbonated, crystal clear, and ready to present to participants the following weekend.

| RESULTS |

Over the course of 4 days, 22 people graciously donated their palates to this cause. All tasters were blindly served 1 sample of the cool fermentation beer and 2 samples of the warm fermentation beer then asked to choose the one they perceived as being most different. In order to reach a statistical significance, 11 (tasters (p<0.05) would be expected to accurately select the odd-beer-out, while 12 (p=0.017) participants were capable of doing so. While this does not allow us to conclude with certainly that fermentation temperature does indeed have a significant impact on the character of a beer, what this suggests is that the probability this data occurred by chance is significantly low enough to allow us to comfortably doubt the null hypothesis (that the beers are indistinguishable).

Similar to prior xBmts, the comparative survey completed by the 12 participants who were correct on the triangle test yielded data of seemingly little consistency. In terms of aroma, 5 people perceived them as being exactly the same, another 6 thought they were somewhat similar, and only 1 felt they were not at all similar; of the 7 who perceived some similarities, 5 preferred the aroma of the cool fermentation sample. Regarding flavor, 2 thought they were exactly the same, 8 said they tasted somewhat similar, and only 2 perceived them as being not at all similar; flavor preference for the 10 who noted some similarities between the beers was split right down the middle. Finally, 7 of the 12 tasters perceived the beers as being exactly the same when it came to mouthfeel, with 3 experiencing some similarities and 2 saying they were not at all similar; interestingly, of the 5 who reported noticing some similarities, 4 endorsed the cool fermentation batch as being their preferred, with comments suggesting it was “less watery” and “more rounded.”

Toward the end of the survey, the nature of the xBmt was revealed to those participants who were correct on the triangle test and they were asked to guess which beer they believed was fermented cool. Surprisingly, a rather large majority (8) wrongly selected the beer that was fermented warm.

Oh, and not a single comment on esters, phenols, fusels, or other yeast derived off-flavors.

My Impressions: I’m a bit perplexed. Sure, we reached statistical significance, if but by a mere skosh. But I’m telling you, if you were to serve me a pint of one of these beers immediately I finished a pint of the other, I’m certain I wouldn’t notice the change. The differences, which were subtle at best, only became apparent to my biased palate only as I focused on the tiniest of details. In fact, the only real difference I could pick up, the one aspect that allowed me to accurately select the odd-beer-out in 4/5 semi-blind triangle tests, is what I perceived as a difference in mouthfeel, as noted by a couple tasters. The fact more than half of those who moved onto the comparative evaluation really surprised, I figured that was the dead giveaway. I’m left wondering, despite the results, how the hell a beer fermented at 76°F with a notably characterful English yeast strain wasn’t the outright ester bomb I expected? Why didn’t a larger majority of these experienced tasters notice the difference immediately? Comparing the beers side by side, even knowing the nature of the difference, I found them to be nearly identical, save for the slightly watery finish of the warm fermentation batch. Yeesh.

| DISCUSSION |

Along with many others who’ve been in the hobby for awhile, I’ve stated multiple times that one of the absolute best things a homebrewer can do to make better beer is control fermentation temperatures. Admittedly, this sentiment was hugely influenced by those I look up to and whose opinions I value, though it was also based on personal experience– it’s true that my beer got better when I rigged up an old chest freezer to control the temperature of my fermentations. Sure, I made a few other process changes around the same time, like pitching healthy yeast starters, but the whole temp control thing, I mean, it just seemed so fucking obvious. It’s weird, as I sit here digesting the fact we achieved significant results for the second time ever, my focus seems to easily shift to how incredibly similar the beers actually were, how incredibly close were were to not achieving significance. Huh.

So, I’ll continue with my regular process of fermenting beer at cooler temps, primarily because it has worked for me, though I suppose it does feel sort of good knowing there’s some data to back this practice up.

What’s your experience been when it comes to fermentation temperature? Since starting this project, I’ve heard from a few folks who swear it doesn’t matter nearly as much as many of us believe, while others still maintain it’s an essential component of good beer production. Please feel free to share your thoughts in the comments section below.

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