Author: Jake Huolihan

For many brewers, reducing the temperature of beer once fermentation is complete, a method referred to as cold crashing, is common practice. Colder temperatures encourage the flocculation of yeast and other particulates, making them heavy enough to drop out of solution, thus leading to improved clarity. When used in conjunction with fining agents such as gelatin, the effect is often enhanced, resulting in both higher yield and clearer beer in the package.

The simplest approach to cold crashing involves making a single adjustment to the controller such that the temperature of the beer is rapidly reduced. Critics of this approach contend that such quick chilling can “shock” yeast, potentially causing them to excrete compounds that lead to undesirable off-flavors. The solution involves reducing the temperature more gradually, 3-5°F/2-3°C per day until it reaches the desired point, which allows the yeast time to acclimate to the cooler environment.

I’ve not regularly cold-crashed in awhile, mostly due to fears of cold-side oxidation, but I’ve used both methods numerous times in the past and can’t say either led to notably bad beer. To better evaluate the impact cold crash speed has, I designed an xBmt to test it out for myself!

| PURPOSE |

To evaluate the differences between beers where the cold occurred either immediately after fermentation or in a gradual manner.

| METHODS |

In hopes of allowing any subtle flavors caused by cold crash speed to shine through, I went with a simple Helles for this xBmt.

Climate Change

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 44.7 IBUs 4.5 SRM 1.053 1.016 4.8 % Actuals 1.053 1.015 5.0 % Fermentables Name Amount % Odyssey Pilsner 11.5 lbs 96.84 Carahell (Weyermann) 4 oz 2.11 Melanoidin (Weyermann) 2 oz 1.05 Hops Name Amount Time Use Form Alpha % Loral 24 g 60 min Boil Pellet 10.3 Loral 15 g 30 min Boil Pellet 10.3 Yeast Name Lab Attenuation Temperature Harvest (L17) Imperial Yeast 72% 50°F - 60°F Notes Water Profile: Ca 49 | Mg 0 | Na 8 | SO4 38 | Cl 61 Download Download this recipe's BeerXML file

The night before brewing, I weighed out the grains and collected the water in my kettle, adjusting it to my desired profile. After setting my controller to heat the water first thing the next morning, I milled the grain.

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

The mash was left alone for 60 minutes.

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

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

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

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

Identical volumes of wort were racked to separate sanitized Unitanks.

The filled vessels were connected to my glycol rig and left to finish chilling to my desired fermentation temperature of 50°F/10°C. This took about 15 minutes, at which point I direct pitched a pouch of Imperial Yeast L17 Harvest into each batch then hit both with a dose of pure oxygen.

I observed decreased fermentation activity after 5 days, so I capped each Unitank and allowed each to pressurize to 10 psi. At this point, I also raised the temperature of the beers to 56°F/13°C for a diacetyl rest. The beers were left alone for another week to ensure fermentation was complete before introducing the variable. Hydrometer measurements at this point confirmed both had reached the same FG.

For one batch, I set the controller on my glycol chiller to 36°F/2°C to encourage a rapid reduction in temperature; the entire batch of beer stabilized at this lower temperature in just over an hour. For the other beer, I lowered the temperature just 1°F/0.5°C every 12 hours until it was at the same 36°F/2°C, a total of 10 days. The following day, I pressure transferred both beers to sanitized and CO2 purged kegs that were then placed in my keezer. Following burst carbonation and a period of conditioning, they were ready to serve to tasters.

| RESULTS |

Cheers to Denver’s CO-Brew Homebrewing Supplies for allowing me to collect data at their shop!

A total of 21 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples quick cold crash beer and 1 sample of the beer cold crashed gradually in different colored opaque cups then asked to identify the unique sample. While 12 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, only 5 (p=0.89) did, indicating participants in this xBmt were unable to reliably distinguish a Helles cold crashed from 56°F/13°C to 36°F/2°F in 1 hour from one cold crashed gradually over a 10 day period.

My Impressions: Out of the 5 triangle tests I attempted, I happened to correctly guess the unique sample just 2 times. To my palate, the beers were identical, possessing the exact same rich, bready Helles flavor I know and love. This may quite possibly be the best Helles I’ve brewed to date.

| DISCUSSION |

For brewers who have a means of fermentation temperature control and want to package beer with little to no particulate, cold crashing is a no-brainer that will certainly cause yeast, hops, and other compounds to drop out of solution. The ideal time-frame to lower the beer temperature to just above freezing is up for debate, a common belief being that a gradual reduction will result in less yeast stress and thus a lower risk of off-flavor development. In contrast to these claims, tasters in this xBmt were unable to differentiate a Helles cold crashed from 56°F/13°C to 36°F/2°F in 1 hour from one cold crashed gradually over a 10 day period.

There’s no denying that yeast can emit compounds that contribute to undesirable off-flavors when under stress, and an environment that goes from warm to nearly freezing quickly is arguably more stressful than a more gradual reduction– consider the fable of the boiling frog. Similar to the truth behind this mythical tale, the results of this xBmt suggest that even when cold crashed faster than most homebrewers can reasonably achieve, the impact is minimal enough so as not to be perceptible.

I’ve long adhered to convention when it comes to cold crash speed and was fairly convinced the fast cold crash beer in this xBmt would have issues. The fact my experience with the beers aligned with the blind taster data left me with a sense of comfort that overshadowed my surprise. In the end, I definitely plan to decrease my cold crashing times in the future as a result of this xBmt.

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

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