Author: Jake Huolihan

Fermentation temperature receives a lot of attention from brewers interested in producing the best beer possible, as different yeasts are known respond favorably to certain temperature ranges. For example, while fermenting at 85°F/29°C is perfectly appropriate for a Saison, it’d likely lead to an undesirable mess in a German Pils. It’s for this reason many brewers invest in some form of fermentation temperature control, the goal of which is to ensure the fermenting beer maintains a set temperature throughout fermentation.

Those who don’t have a source of fermentation temperature control often rely on methods that, while arguably effective, lead to notable temperature swings during the process. As an exothermic process, fermentation can raise the temperature of beer by 7-10°F/4-6°C all on its own if left uncontrolled, which is usually enough to push it well outside of the recommended range. In response to various past xBmts suggesting specific fermentation temperatures may have less of an impact than expected, some have proposed the issue may not necessarily be the set temperature, but rather temperature variability during fermentation that negatively affects beer.

When results from a recent xBmt suggested tasters could not distinguish a Pale Ale fermented at a stable 66°F/19°C from one where the temperature was intermittently varied by 20°F/11°C, I was surprised and began to wonder if this would also be the case for a pale lager, a style many believe requires consistently cool temperatures in order to avoid off-flavors. With the ability to very precisely control fermentation temperature, I designed an xBmt to test it out for myself.

| PURPOSE |

To evaluate the differences between pale lagers fermented either at a stable temperature or in an environment where the temperature was highly variable throughout the fermentation process.

| METHODS |

For this xBmt, I went with a simple Czech Pale Lager recipe made with a commonly used traditional lager strain.

Disparate Times

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 49.7 IBUs 4.7 SRM 1.049 1.015 4.5 % Actuals 1.049 1.015 4.5 % Fermentables Name Amount % IdaPils (Cargill) 10.5 lbs 95.45 Melanoidin (Weyermann) 8 oz 4.55 Hops Name Amount Time Use Form Alpha % Tettnang 45 g 60 min Boil Pellet 4.5 Tettnang 53 g 30 min Boil Pellet 4.5 Tettnang 45 g 3 min Boil Pellet 4.5 Yeast Name Lab Attenuation Temperature Urkel (L28) Imperial Yeast 73% 52°F - 58°F Notes Water Profile: Ca 41 | Mg 0 | Na 8 | SO4 45 | Cl 42

Download Download this recipe's BeerXML file

My first order of business on brew day was weighing out and milling the grain for a 10 gallon/38 liter batch that would later be split.

With the water adequately heated, I stirred in the grist then checked to ensure it was at my target mash temperature.

The mash was left to rest for 60 minutes with intermittent stirring.

When the mash rest was complete, I transferred the sweet wort from the MLT to the kettle.

During the lautering process, I weighed out the kettle hop additions.

The wort was then boiled for 60 minutes with hops added as listed in the recipe.

Once the boil was complete, I quickly chilled the wort.

A refractometer reading showed the wort was right at my target OG.

Identical volumes of wort were racked to separate sanitized Brew Buckets.

The filled vessels were connected to my glycol rig and left to finish chilling to a fairly standard lager fermentation temperature of 50°F/10°C, which took approximately 20 minutes. At this point, I set the hysteresis on one controller to 0.5°F/0.3°C while the other was set to 6°F/3.3°C. To be clear, this meant one batch would maintain a stable 50°F/10°C while the other would get up to 56°F/13.3°C every hour or so before being chilled back down to the set point.

I then pitched a fresh pouch of Imperial Yeast L28 Urkel into each batch before hitting them with 120 seconds of pure oxygen.

As fermentation began to slow 5 days post-pitch, I set the hysteresis on both batches to 1°F/0.6°C in order to prevent suck-back of airlock fluid caused by the vacuum created during the chilling of the variable temperature beer. With activity all but absent after another 5 days, 10 total since pitch, I took a hydrometer measurement indicating both had reached the expected FG.

When a second measurement taken 2 days later showed no change, I pressure transferred the beers to separate kegs.

The filled kegs were placed in my keezer and burst carbonated overnight before I reduced the gas to serving pressure. After a couple weeks of conditioning, they were carbonated and ready to serve to participants.

| RESULTS |

A total of 19 people of varying levels of experience participated in this xBmt. Each participant was served 1 sample of the beer fermented at a stable temperature and 2 samples of the beer fermented at a variable temperature in different colored opaque cups then asked to identify the unique sample. While 10 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, only 6 (p=0.65) did, indicating participants in this xBmt were unable to reliably distinguish a pale lager fermented at a consistent 50°F/10°C from one where the temperature varied by 6°F/3.3°C.

My Impressions: of the 5 semi-blind triangle tests I attempted on these beers, I chose the unique sample just twice, and I’ll admit that I guessed every time. Both beers were great, a good thing seeing as they tasted identical to me.

| DISCUSSION |

When it comes to producing the finest lager possible, it’s commonly believed that one must ferment cool, which given certain environmental factors, often requires something to allow the brewer to maintain a steady temperature. In the event a lager beer falls too far outside of the recommended temperature range during fermentation, the results will be noticeable and unfortunate. However, the fact tasters in this xBmt were unable to reliably distinguish a pale lager fermented at a stable 50°F/10°C from one where the fermentation temperature varied by up to 6°F/3.3°C calls this notion into question.

In considering possible explanations for these findings, I couldn’t help but think of the past xBmts demonstrating lagers fermented at fairly large temperature differences were indistinguishable by tasters. If it’s true that such yeasts are more robust than many believe and, at least on the homebrew scale, don’t lead to noticeable off-flavors when fermented close to typical ale temperature, then it makes at least some sense that a swing of just 6°F/3.3°C wouldn’t be detrimental. Of course, there’s also the argument that temperature variability regardless of actual fermentation temperature puts stress on yeast that can lead to off-flavor production. Based on these results, it would seem the yeast had developed adequate enough skills to cope with the added stress.

I currently use a glycol rig to control fermentation temperature, which makes maintaining a stable temperature very easy. But for those brewers relying on less technological methods such as adding frozen water bottles to an ice bath, temperature swings during fermentation are a real concern, especially when making lagers. While these findings certainly aren’t conclusive, the fact neither tasters nor I could tell a difference between these xBmt beers leaves me at least moderately comfortable encouraging those who, due to an inability to precisely control fermentation temperature, may have avoided making lagers in the past to give it a shot and see how it works.

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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