Author: Matt Del Fiacco

Some of the most astounding xBmt results for me have been those showing the same beers fermented at different temperatures are largely indistinguishable by blind tasters. Of the 6 completed xBmts focused on this variable, only 2 have returned significant results– tasters could tell apart Milds fermented with WLP002 English Ale yeast at either 66°F/19°C or 76°F/24°C as well as Helles’ fermented with Saflager W-34/70 at either 60°F/16°C or 82°F/28°C. These findings just do not jibe with what I’ve learned about fermentation, and based on the number of accounts from homebrewers who swear that fermentation temperature control was key to the improvement of their beer, it’s clear I’m not alone.

Why can’t tasters tell apart beers fermented at such drastically different temperatures?!

One of the more common speculations has to do not so much with the actual temperature, but rather changes in temperature during fermentation. It seems a valid point given most new homebrewers rely on closets and corners without much in the way of temperature control other than their home’s thermostat. It’s entirely possible a correlation exists between newness in the hobby and off-flavors typically associated with poor control of fermentation temperature; however, as anyone who has taken Stats 101 is aware, correlation does not causation make, which is why I decided to see what would happen if temperature during fermentation was a bit less stable!



| PURPOSE |

To evaluate the differences between a beer fermented at a stable temperature and a beer of the same recipe fermented in an environment where the temperature was intentionally varied by 20°F up and down throughout the fermentation process.

| METHODS |

With so many non-significant prior xBmts on this variable, I thought it’d be best to brew a clean and simple beer so that any differences are more easily identifiable, which worked out well since the Willmette beer recently evaluated for the recent The Hop Chronicles fit the bill nicely.

Smooth & Steady, or Go Down Swingin’?

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 30.1 IBUs 3.4 SRM 1.049 1.012 4.8 % Actuals 1.049 1.012 4.8 % Fermentables Name Amount % Pilsner (Weyermann) 11.25 lbs 100 Hops Name Amount Time Use Form Alpha % Willamette 28 g 60 min Boil Pellet 3.6 Willamette 39 g 25 min Boil Pellet 3.6 Willamette 67 g 5 min Boil Pellet 3.6 Willamette 28 g 3 days Dry Hop Pellet 3.6 Yeast Name Lab Attenuation Temperature American Ale (1056) Wyeast Labs 75% 60°F - 72°F Notes Water Profile: Ca 80 | Mg 2 | Na 10 | SO4 125 | Cl 62



I made a starter of Wyeast 1056 American Ale yeast a couple days beforehand, sizing it such that it would provide enough yeast after being split between 2 batches.

The next morning, I immediately began by heating RO water for a full-volume no sparge batch, adjusting it to my mineral profile.

Grains were weighed out and milled as the water was on the flame.

Once the water had reached strike temperature, I added the grist filled Brew Bag to the water and gave it a gentle stir to ensure there were no dough-balls.

The temperature stabilized nicely at my target mash temperature of 153°F/67°C.

The wort was continuously recirculated throughout the mash rest. After 15 minutes, I stole a small sample for a pH measurement that showed I’d hit my target.

I weighed out the kettle hop additions during the 60 minute saccharification rest.

Once the mash was finished, I removed the grain bag and brought the remaining wort to a rolling boil.

After 60 minutes and a few hop additions, I quickly chilled the wort then took a refractometer measurement.

The wort was evenly split between two 3 gallon Better Bottles, each placed in a cool chamber to finish chilling to my target pitching temperature.

Once at 64°F/18°C, I pitched identical amounts of Wyeast 1056 starter into each carboy and set the chamber for the stable temperature batch to maintain my desired 66°F/19°C; however, the variable temperature batch was allowed to free-rise during the first eight hours of fermentation. After those first eight hours, I plugged the heat wrap in to the temperature controller and ramped it up to 86°F/30°C. After the first 12 hour window was over, the swing temperature beer (right) was showing more aggressive signs of fermentation than the stable temperature beer (left).

Over the course of the next 7 days, I forced the variable temperature beer up or down in temperature ranging from 66°F/19°C to 86°F/30°C every 12 hours. At the end of that week, with signs of fermentation having diminished, I took hydrometer measurements showing both beers appeared to have attenuated the same.

Dry hops were added to both batches at the same time, when fermentation was dying down, and they were left alone for 48 hours before I proceeded with cold crashing, fining with gelatin, and kegging.

I burst carbonated overnight then reduced the CO2 to serving pressure where it sat for a few more days before I began serving it to participants.

| RESULTS |

A panel of 22 people with varying levels of experience participated in this xBmt. Each taster, blind to the variable being investigated, was served 1 sample of the beer fermented at a stable temperature and 2 samples of the beer fermented at variable temperatures in different colored opaque cups then instructed to select the unique sample. While a total of 12 correct selections would have been required to achieve statistical significance, 11 tasters accurately identified the unique sample (p<0.05; p=0.08), suggesting participants in this xBmt were unable to reliably distinguish a Pale Ale fermented with the popular Wyeast 1056 at a stable 66˚F/19˚C from the same beer fermented at varying temperatures.

While “but dude, it was so close!” doesn’t really matter, I figured I’d share some of the preference data, just please interpret with a grain of salt. Of the 11 people who correctly chose the unique sample in the triangle test, 2 said they preferred the one fermented at a stable temperature, 6 reported preferring the variable temperature beer, 2 had no preference despite noticing a difference, and 1 person felt there was no difference between the beers.

My Impressions: To quote my friend Tim, “The swing temp tastes like cake”. In three blind triangles, I could identify the swing temp beer every time. Not only did I taste what I typically associate with diacetyl, but there was a dough-y sort of sweet character that just wasn’t present in the stable fermented beer. I was blown away by these results, I’d even go so far as to say that I’m uncomfortable with them. At the same time, I’m excited by the possibility that there may be methods for new brewers to produce good beer without temperature control, and excited that we may open up other avenues of “what sets good beer apart”.

| DISCUSSION |

For those who might currently be feeling like these results were “close enough” to significant that it’s possible variable fermentation temperature does have a noticeable impact on beer and this xBmt missed it for whatever reason, you’re not alone. In situations like this, where if 1 more taster had been right instead of wrong the conclusion would be different, particularly with a variable as sensitive as fermentation temperature, I feel a strong pull to explain away and minimize the findings, which I’m aware is at least in part due to the fact they don’t align with my expectations.

But then I took a step back and thought about things a little deeper…

In this xBmt, the batch fermented with swinging temperatures was treated in a way that’s arguably unrealistic for most homebrewers in that I forced vast temperature variations in order to coax out a difference. Whereas the typical homebrewer who ferments their beer in a 68°F/20°C basement or closet may experience relatively gradual swings of about 7°F/4°C, I forced intermittent changes of 20°F/11°C (66°F/19°C to 86°F/30°C throughout fermentation, more than double what one might expect to occur naturally. If variations in temperature during fermentation were to have a perceivable impact, I have to believe the comically bipolar environment I created would have done the trick, and yet participants in this xBmt were incapable of reliably detecting a difference.

There’s no way I’d say these results prove that temperature variations during fermentation don’t matter, just as we’d never claim that fermentation temperature when using traditional lager yeasts doesn’t despite numerous xBmts demonstrating it doesn’t seem to produce a reliably distinguishable difference. It’s entirely possible two of the tasters had coffee before our test, and that is why this did not come back significant. Or, it’s possible that if you throw enough healthy yeast at something that there’s more room for errors. Or, as our previous xbmts suggested, maybe it really depends on the yeast strain. I’m of the opinion that a combination of those things is likely true, and if there’s anything I personally am going to walk away from this xbmt with it is a hope to see more testing and reports on this variable.

If you have thoughts about this xBmt, please share them in the comments section below!

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