Cold Crashing

Unfortunately, the pathway to diacetyl includes the possibility of more diacetyl formation (above a taste threshold) after what was already there was cleaned up (to below a taste threshold). I guess I've been lucky in that I haven't had this happen with any of my beers. But if this has happened to you more than once, maybe consider doing a forced diacetyl test. That should tell you pretty definitively if there is still diacetyl precursor in your beer.

 

I did a force test recently, and it did seem helpful, at the time, showing diacetyl, and then not showing it after an extended rest. But for my extra work, I still have diacetyl in that keg. I'm thinking that this used to not be problematic back when I bottled because I primed and activated the yeast, and then let it sit at 65-70 degrees for several weeks to clean up. With kegs, I chill after moving to the keg and force carbonate, but I guess those other pathways to diacetyl are not sufficiently impaired by chilling, and the yeast are not so active to clean up. I know infection is another pathway to diacetyl, but I'm thinking that any infection agent would be impaired by the chilling too. It's not every beer that gives me this problem, but it's showing up pretty regularly.

 

An important thing about diacetyl formation, which a lot of articles/blogs ignore or gloss over, is that yeast make diacetyl's precursor, but they don't make diacetyl...it's made by oxidation of the precursor in the wort. The yeast do clean up diacetyl once it's made. I suspect you are correct in that cold probably impairs the yeast more than it slows oxidation of precursor, which is why it's important (if your beers/process are prone to diacetyl) to make sure it's all gone before shutting the yeast down.

So after the long rest, you did a force test that showed no diacetyl, then kegged and ultimately ended up with diacetyl in the keg? That's a little surprising. How long did you force? I wonder if there was precursor in the sample, but the force was long enough that it converted and cleaned up before you tasted it. Just a thought. I've never done a diacetyl force test, but have read about them enough times to understand the process.

 

The diacetyl forms outside the yeast cell due to the oxidation, higher temps form it faster. Kara Taylor of White labs gave a good talk on Diacetyl at last years NHC.

Peter, be careful when racking or bottling, as O2 exposure will produce Diacetyl if any precursor is in the beer. I have had that happen when bottling for competitions.

 

Is the optimum around 3C?

 

Good stuff in here. I had been thinking about diacetyl formation as a biotic process, rather than a series of biotic and abiotic processes, which is a really big impact on my understanding.

When you say how long did I force, I'm not sure what you mean. The force test I did involved briefly heating a sample to some designated temp and then sniffing it. Do you mean how long did I heat? I'd have to review the details as it's been a couple months. I think it is possible that I overshot the temp and didn't think much of it.

 

Yes.

 

Narziss provides the following "chart" for achieving optimum consumption of remaining extract:

day temp % remaining extract
0 4.5 1.3
3 3.0 0.9
7 2.7 0.7
14 1.0 0.5
21 0.0 0.4
35 -0.7 0.3
49 -1.0 0.2
63 -1.3 0.1

 

Good perspective. I will only add that I have tried both approaches (in a number of different areas/processes) and found that the techniques put forth and supported by folks like Narziss and German brewers inevitably create beers that are more like the ones I drank in Germany/Czech Rep (and those brewers almost all utilize the same techniques Narziss puts forth as well).

 

So that is the tradition technique, more or less. My guess is that a spunding valve is used, correct?

 

Spunding valve is used, yes (except for ungespundete biers ).

 

I guess I do a hybrid cold crash. I don't drop 1° per day, more like 5° so I can hit my desired lagering temp within a couple days rather than weeks. As usual I only have anecdotal evidence, but I've always found my lagers to be lacking somewhat when I drop from say 50° to 32° in a couple hours and drop all the suspended yeast out. As mentioned some yeast activity does occur under lagering conditions, in my mind it makes sense to ensure some of that yeast stays in suspension, an immediate cold crash will shock them into floccing. I suppose this also depends on the yeast strain, some may be more tolerant of extreme temperature changes.

 

I sincerely doubt that a homebrewer could achieve a cold crash as you indicated here. A 5+ gallon batch of beer has a lot of thermal mass and even if you placed a beer at 50 degrees F in a chamber set for 32 degrees F it would take quite some time (i.e., much longer than 2 hours) for the beer to reach a temperature of 32 degrees F.

Cheers!

 

True, lets just say overnight then.

 

Fair enough.

I personally do not achieve a change of 50 degrees F to 32 degrees F overnight but I suppose other homebrewers could.

Cheers!

 

Guess I never timed it, I feel fairly certain my chest freezer could drop 5.25g of beer 18 degrees in an 8 hr period. Either way I personally feel an extended cold crash to be more beneficial to my beer than a quick one.

 

It is entirely possible that your chest freezer could achieve this. Since I have personally not used your chest freezer I have no way of knowing this for certain. I can report that for my homebrewed lagers I have never gotten from 50 degrees F to 32 degrees F in that time period. I can also report that in my homebrewing the yeast does indeed perform 'stuff' over the 5-6 weeks that I lager my lager beers.

Cheers!

 

Yep let's focus on how fast my freezer can cold crash my beer. I'm sure that's exactly what the OP had in mind. My point remains the same regardless.

 

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