Author: Jake Huolihan

A technique used by brewers to ensure the transfer of clean, clear beer to its target package is cold crashing, which generally involves reducing the temperature of the fermented beer prior to packaging. This works because rapidly decreasing the temperature of a colloidal solution encourages the coagulation of particulates such as proteins and yeast, and as these particulates coagulate, they become heavy enough to drop out of solution. There’s more that goes into it than that, but suffice to say, cold crashing beer tends to result in a densely packed trub layer and clearer beer.

The benefits of cold crashing aren’t limited to just clarity of the finished beer, it also allows for a much easier racking experience since particulates that could clog a siphon or diptube have dropped out of solution, even on highly dry hopped beers. The method also has its downsides such as the fact it requires a brewer to have the ability to control temperatures and it also extends the time the beer needs to stay in the chamber. Another potential drawback of cold crashing that seems to have caught some attention of late has to do with the vacuum created as the beer cools, which results in the beer being exposed to both airlock fluid and oxygen from the chamber environment.

I’ve cold crashed many times over the years and it always seemed to do as promised, my beers tend to clear up quickly even without the use of finings. I hadn’t really questioned this technique much, as it has become a ubiquitous practice among brewers and my own experience has been largely positive. That said, I won’t pretend the suck-back issue didn’t make me nervous, not so much about the airlock liquid since I use sanitizer, but it seemed an obvious vector for oxidation. This anxiety was amplified by the results of a recent xBmt showing not only that oxygen exposure on the cold-side led to a distinguishable aroma and flavor difference, but that it also caused the beer to darken quickly. I began to wonder if cold crashing was the culprit and decided test it out to see for myself!

| PURPOSE |

To evaluate the differences between a German Pilsner that was cold crashed in the fermentation vessel prior to being kegged and one that was kegged warm.

| METHODS |

I chose to make a delicate German Lager for this xBmt thinking it would allow any differences caused by a potentially subtle variable to shine through.

Autobahn

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 32.3 IBUs 4.1 SRM 1.050 1.010 5.2 % Actuals 1.05 1.01 5.2 % Fermentables Name Amount % Weyermann Pilsner Malt 9.625 lbs 88.51 Munich II (Weyermann) 1 lbs 9.2 Carahell 4 oz 2.3 Hops Name Amount Time Use Form Alpha % Hallertau Magnum 18 g 60 min Boil Pellet 11.5 Hallertau 21 g 30 min Boil Pellet 2.3 Hallertau 28 g 10 min Boil Pellet 2.3 Yeast Name Lab Attenuation Temperature Global (L13) Imperial Yeast 75% 46°F - 56°F Notes Water Profile: Ca 71 | Mg 0 | Na 8 | SO4 75 | Cl 75 Download Download this recipe's BeerXML file

A few days prior to brewing, I whipped up a large starter of IOY L13 Global yeast, which is quickly becoming a go-to strain for me.

On the morning of brew day, after my future brewing assistant woke me up earlier than I would have liked, I collected my water, adjusted it to my desired profile, then milled my grains while it was warming up.

Once the water was at strike temperature, I added the bag of grains and realized this 10 gallon no sparge BIAB batch was pushing the limits of my 20 gallon kettle.

After given the grains a gentle stir, I checked to ensure I hit my target mash temperature.

I turned my pump on at this point and let the mash recirculate for the duration of the 60 minute saccharification rest, after which I removed the grain bag and let it drip to reach pre-boil volume while the sweet wort was heating. The wort was then boiled for 60 minutes with hops added as stated in the recipe.

With the boil complete, I quickly chilled the wort to 70°F/21°C.

A hydrometer measurement confirmed I’d achieved my target OG.

The wort was evenly split between 2 Brew Bucket that I placed next to each other in my chamber where they were left overnight to finish chilling to my desired fermentation temperature of 50°F/10°C.

The following morning, I evenly split a decanted starter between the batches before hitting each with a 90 second dose of pure oxygen. I checked on them the next day and found both were actively fermenting. I left the beers alone for 2 weeks, at which point no observable signs of fermentation were present, so I took hydrometer measurements indicating both had reached FG.

I bumped the chamber up to 60°F/16°C for a day diacetyl rest. After 1 day at this warmer temperature, the time had come to introduce the variable. Since the purpose of this xBmt was to evaluate the impact cold crashing in a fermentation vessel has on beer, I opted to keg the non-crashed beer at the same time I reduced the chamber to a cold crash temperature of 32°F/0°C.

I noticed the next day that a noticeable amount of the sanitizer in my airlock had been sucked into the beer, undoubtedly accompanied by an unknown amount of oxygen.

After 2 days of cold crashing, I racked the beer to a keg that was placed next to the non-crashed beer in my keezer. Both were briefly burst carbonated before I reduced the gas to serving pressure and let them cold condition. I took samples at 3 weeks to see if there were any noticeable differences in color or clarity and found that, at least to my eyes, they looked the same.

While clarity is a purported benefit of cold crashing, we were curious if the introduction of oxygen that occurs when using the method would have an impact, hence the beers were allowed to age another week before I began collecting data. Again, they looked the same in every respect to me, but how would they taste?

| RESULTS |

A panel of 26 people with varying degrees of experience participated in this xBmt. Each taster, blind to the variable being investigated, was served 2 samples of the cold crashed beer and 1 sample of the beer that was packaged warm in different colored opaque cups then instructed to select the unique sample. At this sample size, a total of 14 (p<0.05) correct selections would have been required to achieve statistical significance, while only 9 tasters (p=0.52) chose the different beer, indicating tasters were not able to reliably distinguish a German Pilsner that was cold crashed prior to packaging from one that was not.

My Impressions: In multiple blind triangles, I was unable to identify the odd-beer-out and resorted to guessing every time. They tasted, smelled, and looked identical to me. And the beer was so good! Substituting my normal charge of Vienna for some Munich II gave it a deep golden color that I found very pleasant. I absolutely plan to make this recipe again.

| DISCUSSION |

While many brewers have adopted the practice of cold crashing to aid in the clarification of their beer, others have questioned whether it might be more detrimental than it’s worth given the fact it usually results in oxygen being sucked into the fermentation vessel. Admittedly, after reading the results of the cold-side oxidation xBmt, I was convinced cold crashing was the culprit and expected the Pilsners from the present xBmt to be noticeably different. However, not only were blind participants unable to reliably distinguish the cold crashed beer from the one packaged warm, but I couldn’t either, they were similar in every respect.

It might be easy to take these findings as some sort of proof cold crashing is a waste of time, and while it may not be totally necessary, it has its benefits in certain situations. For example, when making a heavily dry hopped IPA, especially when the hops are added loose, a good cold crash will encourage a lot of that hop matter to the bottom of the fermentor thereby making packaging less of a mess. I’ve also noticed the trub cake after cold crashing is more compact, meaning there’s a lower risk of transferring that unwanted gunk to the keg or bottling bucket.

I won’t be forgoing the step of cold crashing in my brewing, though considering these results in light of the aforementioned NEIPA xBmt, I’m left scratching my head as to what in the world could be causing the hasty degradation of those beers. I suppose the next step would be isolating the variable of oxygen exposure at packaging, though based on my personal experience, I’m not convinced that alone is the answer. And so the search continues…

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

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