Cold Crashing

I've never had any issue with just throwing some sanitized foil/saran-wrap over the top of the carboy and letting it sit.

My thinking on why that doesn't oxygenate the beer is as follows:

1) CO2 is heavier than air, so it will tend to lay low and maintain a buffer layer between the outside air and the beer.
2) Realistically, at cold-crash temperatures you'll only see ~6-7% reduction in volume (source) which means not that much air is getting sucked in to begin with.

Cheers!

 

I wouldn't say that I've had problems with the air sucking back in, but it's not something I like, so I cap my fermenter now when I start to chill it (I have a speidel, and it comes with a cap). You could do the same with a stopper and a carboy. The times I've noticed suck-back in a big way was when the temp was around 40 F. The problem is that not only does the pressure drop inside the carboy, causing air to come through the air-lock, but CO2 is more soluble at lower temps than higher temps, so it will start to re-absorb into the beer, and pull more air in.

Still, the beer's cold, and it has a lot of yeast in it, so the air suck-back is probably not going to kill it.

 

“Is that at risk of oxygenating the beer?” If the yeast is completely done fermenting then yes, there is a risk of oxidizing the beer. What @FarmerTed does of capping his fermenter is a good idea in that it completely stops air (oxygen) from entering the fermenter.

I cold crash my lagers while using an airlock but I do not concern myself with oxidation since the yeast in my lagers still conduct a small amount of fermentation while lagering; the yeast will consume the small amount of air (oxygen) that may enter during the cold crash process.

Maybe get a stopper for you carboy (assuming that you use a carboy as your fermenter)?

Cheers!

 

Assuming the OPs attenuation is finished before cold crashing, there won't be any more fermentation. And even if there were, and even if the yeast stay active at the lower temperature, no additional oxygen would be used. Oxygen is used to build sterols in preparation for budding. Yeast that have already reached their maximum density in the beer (which happened early in the fermentation) are not going to prepare for or enter another growth phase in that environment.

 

“It is well-documented that yeast uses oxygen whenever it is available, even during fermentation, and yeast cells rapidly absorb essentially all of the oxygen made available to them”

From the article “The Biochemistry of Yeast”.

Cheers!

 

Where is this well documented?

ETA: If this were true, it would be impossible to oxidize beer that has any living yeast in it.

 

This might be of interest (I can only read the abstract, but it pretty much says it all).


"Improved Flavor Stability by Aging Beer in the Presence of Yeast.Daan Saison (1), David P. De Schutter, Filip Delvaux, and Freddy R. Delvaux, Centre for Malting and Brewing Science, Faculty of Bioscience Engineering, K.U.Leuven, Heverlee, Belgium. (1) Corresponding author. E-mail: <[email protected]>; Phone: +32 16 32 96 27; Fax: +32 16 32 15 76. J. Am. Soc. Brew. Chem. 69(1):50-56, 2011.

Unwanted flavor changes occur during beer storage. Because yeast has a large reducing activity on aging compounds, the aim of this study was to examine the effect of refermentation on flavor stability. It was shown that the addition of yeast to aged beer removed aged flavor almost completely. Furthermore, the addition of yeast to fresh beer decelerated beer aging considerably. Both a top-fermenting and a bottom-fermenting yeast strain were able to exert this effect, and it was clear that initiation of a real refermentation process by adding sugar was not required. Finally, several yeast concentrations were tested, and it appeared that even adding an amount as low as 10,000 yeast cells/mL was sufficient to slow beer aging. Nonetheless, the effect was more pronounced when higher concentrations were used. Keywords: Beer, Flavor stability, Reducing activity, Refermentation, Yeast"


I can't remember the podcast (either the Session or Beersmith), but Charlie Bamforth recently said the same thing. Basically, you can de-stale a beer by adding some active yeast to it.

 

Charlie Bamforth said yeast love the oxidized compounds and will mop those up on the Beersmith podcast recently.

 

This is sort of getting away from the question of yeast using oxygen (dissolved O2) "whenever it is available" (which I read to mean always, and seriously doubt), but this cleanup of oxidized compounds is interesting.

So...if yeast clean up oxidized compounds, but only when the yeast is fresh, I wonder what is the key difference between the fresh yeast and the yeast already in the beer.

 

I heard a lengthy discussion with Bamforth on this topic years ago, it was very interesting. The discussion was regarding hot side aeration and he said that the yeast have a high affinity for oxidized compounds and do such a great job of cleaning them up during primary fermentation that hot side aeration is of no concern whatsoever. Note that he was specifically talking about what goes on during an active fermentation. Whether or not this applies to fresh oxygen introduced to a slowly fermenting beer during cold conditioning I can't say for sure, though I would speculate that it wouldn't be nearly as efficient or effective.

 

I would guess the difference is the active metabolism of the fresh culture.

 

OP - do you keg? If so, just treat that as the cold crash vessel. Purge the keg with CO2. Transfer the beer into the keg. Connect the beer to your CO2 line. As the temperature drops and the pressure naturally decreases, the keg will fill with CO2. No chance of oxidation during your crash. Best way to crash cool homebrew. Cheers.

 

Yes. I believe in excluding O2 at all times after the pre-fermentation wort aeration. Like mattbk, I cold crash in purged kegs.

Keep in mind that not every beer needs to be cold crashed.

 

Which style/type should be cold crashed?

 

For me, it's lagers and Kolsch. Beyond that, I wouldn't cold crash anything unless there was a problem with yeast flocculation.

 

Didn't want to create a new thread, as my question pertains to this topic.

I'm considering cold crashing a SortaSue I've got fermenting right now to settle a bunch of the Citra hop trub down to the bottom before bottling as I plan on just throwing the dry hops into the fermenter. Upon thinking about this further, I came to the conclusion that cold crashing might be better suited for those who keg their beer as I usually lager my bottles for at least a week or so after they have fully carbed and this usually settles out a bunch of trub anyways. Thoughts?

 

I cold crash everything. What's the harm of cold crashing? Benefits are always going to be increased beer clarity and enhanced appearance, obviously. But I've never heard of a drawback to cold crashing.

 

I guess I've just heard it willl then take longer for your bottles to fully carb. And when trying to brew a PseudoSue clone the longer it takes the bottles to carb, the more the Citra hop flavor starts to degrade.