Author: Jake Huolihan

The xBmt results that have shocked me most have been those focused on lager fermentation temperature, there have been 4 with only 1 achieving significant results, and it tested an arguably radical extreme (60˚F/16˚C vs. 82˚F/28˚C). As a staunch believer in the idea that lager beer requires cooler fermentation temperatures, I have to admit I all but convinced myself these findings were more likely due to errors in measurement and perhaps shitty palates than an accurate representation of the impact of temperature on lager fermentation.

Regardless, I was inspired by all of these results. Motivated to both see for myself as well as prove the results wrong, I bit the bullet and fermented a couple batches of lager using a temperature schedule more typical of ale fermentation. Those beers, to my surprise, were great with all of the characteristics I expect in a crisp clean lager– crisp, clean, absent of esters and phenols. I accepted at this point that particular strains might be less sensitive to temperature and that fermenting cool was, to some degree, perhaps an artifact of our less technological past. Curious to explore this variable further, I picked up another lager yeast I’ve come to really enjoy when fermented cool to see how it performs when fermented warm.

| PURPOSE |

To evaluate the differences between beers fermented with WLP940 Mexican Lager yeast at either 50°F/10°C or 66°F/19°C.

| METHODS |

For this xBmt, I went with a beer style known for being fermented with the Grupo Modelo strain, a simple Vienna Lager.

Negra Pared Lager

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 28.1 IBUs 13.0 SRM 1.052 1.017 4.7 % Actuals 1.052 1.017 4.6 % Fermentables Name Amount % Weyermann Vienna 10.5 lbs 97.11 Chocolate Malt 5 oz 2.89 Hops Name Amount Time Use Form Alpha % Hallertau Magnum 12 g 60 min Boil Pellet 14 Hallertauer Mittelfrueh 14 g 30 min Boil Pellet 2.6 Hallertauer Mittelfrueh 14 g 10 min Boil Pellet 2.6 Yeast Name Lab Attenuation Temperature Mexican Lager (WLP940) White Labs 74% 50°F - 55°F Notes Water Profile: Yellow Balanced in Bru’n Water Spreadsheet

Using a pitch rate calculator, I determined the amount of yeast recommended for each batch based on fermentation temperature and made a large starter of WLP940 a few days ahead of time, 2/3 was slated for the cold ferment batch and 1/3 would be pitched into the warm ferment batch.

After adjusting the brewing liquor my desired profile on brew day morning, I turned my element on to heat the liquor then proceeded to weigh out and mill the grain.

Once the water had reached strike temperature, I mashed in then checked the temperature to discover it was a bit higher than I’d intended, which I later discovered was due to a PID probe malfunction that has since been fixed.

I recirculated the mash with the element off to allow the temperature to drop, though I wasn’t too concerned, as the beer would likely have a higher FG and thus lower ABV without being perceptibly sweeter. About 15 minutes into the mash, I took a pH reading that showed I was right on target.

At the end of the 60 minute mash, I hoisted the bag of spent grains out of my kettle and let it drip sweet wort while the wort was heating up.

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

When the boil was finished, I quickly chilled the wort to slightly warmer than my groundwater temperature.

I took a hyrdometer measurement at this point to confirm the wort hit my target OG.

The wort was split evenly between two carboys that were subsequently placed in separate fermentation chambers, one controlled to 50°F/10°C and the other set at 66°F/19°C. They were left alone until the cool ferment wort dropped to the target temperature, at which point I pitched 2/3 of the starter into it and 1/3 into the warm ferment batch. I checked on the beers 24 hours later and observed the cool ferment batch had barely developed a kräusen while the warm ferment beer was ripping away.

Checking in 24 hours later, I noticed the cool ferment beer playing catch-up while the warm ferment beer appeared as though fermentation might be complete. Hydrometer measurements confirmed this was likely true, as the warm ferment batch was sitting at the predicted FG based on the warmer than expected mash temperature.

In order to ensure any differences caused by the variable would be present, I went against my typical process of ramping the temperature up for the cold ferment beer and instead opted to leave it at 50°F/10°C until it reached FG. At 9 days post-pitch, I took another set of hydrometer measurements showing the cool ferment batch was at FG and the warm ferment beer hadn’t changed.

I moved the cool ferment beer next to the warm ferment beer in the 66°F/19°C chamber for a diacetyl rest.

I took a final hydrometer measurement 3 days later that showed no change in either batch, so I cold crashed both overnight, fined with gelatin, and kegged them up.

The filled kegs were placed in my keezer where they were briefly burst carbonated before I reduced the gas to serving pressure. After some conditioning time in my cold keezer, the beers were carbonated and ready to serve to unsuspecting tasters!

| RESULTS |

A total of 27 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the cool ferment beer and 1 sample of the warm ferment beer then asked to identify the sample that was unique. A total of 14 tasters (p<0.05) would have had to select the unique sample to reach statistical significance, which is precisely how many identified the odd-beer-out (p=0.036), suggesting participants were able to reliably distinguish a Vienna Lager fermented with WLP940 yeast at 50°F/10°C from the same beer fermented at 66°F/19°C.

The participants who correctly selected the unique sample in the triangle test were instructed to complete a brief set of additional questions comparing only the two different beers, still blind to the nature of the xBmt. Of the 14 correct tasters, a staggeringly disproportionate 11 chose the cool ferment beer as their most preferred and while not a single person endorsed the warm ferment beer as being better. Two tasters said they noticed a difference but had no preference and only a single taster reported perceiving no difference between the beers.

My Impressions: Over the course of multiple semi-blind triangle tests, I was able to consistently distinguish the warm ferment beer from the cool ferment beer, though it required quite a bit of focus. In fact, trying to describe what it was that made these beers different to my palate is difficult, they just had a slightly different flavor. Both were very good, though with little hesitation, I’d have to say I preferred the one fermented cool. To me, it was slightly more crisp and smooth, while the warm ferment beer had a subtlest hint of something I can only describe as “sharp.”

| DISCUSSION |

Yeasts are living organisms, each strain possessing a unique genetic make-up, and hence it makes sense they’d respond differently to certain environmental pressures. Whereas strains like WLP800 Pilsner Lager yeast and Saflager W-34/70 seem to be less sensitive to temperature, the significant results of this xBmt suggest WLP940 Mexican Lager yeast may not be so robust. What’s even more bewildering to me is the fact all but 3 of the tasters who correctly identified the unique sample in the triangle test selected the cool ferment beer as their most preferred, while not even one liked the warm ferment beer more. The xBmt survey limits our ability to identify what exactly it was that influenced the tasters’ preference for the cool ferment beer, and while my personal preference aligned with theirs, it’s impossible to say if my reasons match the participants’.

Viewing the sensory and preference data together admittedly leaves me with an odd feeling of ambivalence. On one hand, there’s something about this confirmation of the conventionally accepted approach that feels kind of good, a reminder that methods developed eons ago still matter today. However, as someone who appreciates the less time intensive process of fermenting lagers at ale temperatures, I wouldn’t have been bummed out if the beers were indistinguishable. Ultimately, I appreciate these results and will keep them in mind them when using WLP940 in the future, though given how similar I experienced the beers to be, I’ll ferment warm with this yeast again.

One final thing I want to address– claims that a difference in fermentation temperature as small as a couple degrees will produce a noticeable difference. Considering the fact barely half of the participants in this xBmt chose the correct beer in the triangle test when they were fermented 16°F/9°C apart, along with the numerous other non-significant lager fermentation temperature xBmts, it seems worrying over a fermenting beer hitting 50°F/10°C when one planned on 48°F/9°C is likely for naught.

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

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