Krausening in keg

First, krausening and regular priming are two different things. Krausening is adding actively fermenting wort to the beer. Priming (the way most people use the term) is the addition of sugar.

Either way though, it's important to determine what level of CO2 you want, and krausen or prime accordingly. This is true for bottles or for kegs.

With the appropriate amount of sugar, there's no danger of the keg being over-pressurized.

Some will say that you should use less sugar (like 1/2 or 1/3 less) in a keg than you would in bottles. Don't believe it. 5 gallons of beer in a corny keg leaves a headspace that's very close to the total headspaces from bottles filled from 5 gallons of beer (using a standard bottling wand).

Here's a C&P from an old post (mine) on a different forum:
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A standard LHBS "12 oz" bottle measured thusly...
Beer (water, with empty headspace): 12.24 fluid ounces
Headspace: 0.57 fluid ounces
(determined by weighing empty bottle, full bottle, and bottle with headspace displaced/ejected with a closed bottling wand, and doing the math)
Bottle Headspace is: 0.57 oz / (12.24 oz + 0.57 oz) = 4.4%

@doug293cz measured some kegs, and the total volume was 5.3-5.35 gallons, so a headspace of 0.3 to 0.35 gallons.
Keg Headspace is: 0.3 gallons / 5.3 gallons = 5.7% -or- 0.35 gallons / 5.35 gallons = 6.5%.

Because the headspace is actually slightly larger proportionally in a keg than in bottles, the amount of sugar to use would actually be slightly larger for kegs, but they are so close that it really makes little difference.
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People who claim you need less sugar in kegs are also adding CO2 from a CO2 tank some time before the sugar-primed carbonation has finished (which would have over-carbonated if the proper amount of sugar had been used). Or they had a bad experience adding too much sugar (or added sugar to a beer that hadn't finished fermenting), which would have had the same result in bottles. Or they prime with less sugar, let the sugar-primed (under)carbonation finish, then hook up the CO2 tank, and a few days later, carbonation is "perfect," thus "proving" the assertion that less sugar was needed.

 

Krausening is a traditional method of carbonating beer. It evolved prior to brewers having a good way to measure gravity, and it works. You can keep your beer compliant with Reinheitsgebot if you krausen with wort. And you are top cropping yeast, if that appeals to you. Other than that, it does not solve a problem. So ask yourself why you want to krausen instead of priming. Better yet, with kegs you can force carb.

I am not saying krausening it is not an effort worth pursuing (this is a hobby after all), only that among the 100 top things we could put time into, krausening is somewhere after 90. I honestly believe if bottled CO2 was available in 1550 German brewers would have used it.

That is merely one homebrewers opinion.

Directly answering your question, if you do over carb a keg the solution is pretty simple. Release the excess gas by pulling the PRV. Do that as needed. Then when you inevitably apply 12 or 13 psi of bottle gas (which is exactly the same molecule produced through "natural" krausening), the beer will equilibrate. There is zero danger of damaging a Corny (good for 120 psi) choker (good for 60 psi typically) faucet (typically rated to 40 psi) or really anything else. You might blow off a hose clamp but even then the yeast would crap out well before that pressure could be achieved.

Cheers

 

There’s a krausening calculator on Brewers friend. It’s pretty reliable.

I used a scale and did it by weight probably 50 + times.

 

I have been kräusening my lagers for a few years now and I actually think it solves at least one problem: it cleans up that green homebrew lager flavor.

My standard procedure has two parts that take advanced planning: I make a big yeast starter and then save a small jar of the starter. Then when I am transferring the chilled wort of at the end of my brew day I save a 2-liter soda bottle of wort and put it in the freezer. When the beer is close to being done I thaw the wort and pitch the saved yeast (essentially making a kräusening starter). When that starter is at full kräusen I transfer it into a keg and transfer the almost-done-fermenting beer into keg and seal it up and then after a few days I start checking with a spunding valve to relieve excess pressure. (My home-made spunding valve has a small leak somewhere so I don't leave it on the keg.)

Just this past week I had a reminder of another key step. I brewed a Festbier and was hoping to do a split-batch yeast comparison (WLP830 vs. Jasper JY268 - Franconian Lager--AKA TUM35). I decided to ferment in kegs since I don't have other identical fermenters and I was splitting a 6.5 gallon batch. (Unfortunately the WLP830 I have been repitching for a long time finally died and so no experiment--just two kegs with the TUM35). I made the kräusen starter and added them to the kegs last Thursday. When I checked the kegs yesterday with the spunding valve, one was at 15psi and the other was zero. The step I forgot was to blast the kegs with CO2 to set the seal on the keg. One sealed itself and the other didn't.

Another possible explanation is that the keg that didn't seal was basically done fermenting since it had a head start (see failed experiment above), but I have kräusened at various stages of fermentation doneness and have always had it carbonate before (when I set the seal!).

We'll see how different the two kegs taste. I'll start dropping the temp this weekend and lager them until my Oktoberfest party at the end of September.

I enjoy the process and tradition of kräusening. I think natural carbonation this way does give you a different carbonation mouthfeel, I like saving CO2, and I think the process has improved the flavor of my lagers.