handling shrinkage from crash cooling

Question

handling shrinkage from crash cooling

Jason V

2012年9月12日 20:10

I just crashed 5 gallons of German Pilsner for lagering and I noticed that my airlock starsan level was significantly lower after cooling. I presume this is due to the liquid (beer) shrinking after a 20F drop in temp, but I am not sure how to prevent this or protect against it. I am not terribly concerned with starsan going into the carboy, but more that it can drop below the airlock level which essentially is opening up the carboy to the air in the chest freezer.

How do you handle shrinkage when crash cooling in a closed system?

[edit: clarified that i was talking about the beer volume shrinking not the starsan]

Topic lagering crash-cool airlock homebrew

Category Mac

Edwin Buck · Accepted Answer · 2012年9月12日 20:10

Any reduction in temperature will create a negative pressure (compared to what was before) in the fermentation vessel. The air lock is designed to work in a one-way fashion, so the only real risk is contamination of your fermentation chamber with air-lock fluid.

Use a vodka in the airlock instead of starsan. In the extremely rare event that you generate enough low pressure to suck in some of the airlock fluid, you are adding a generally tasteless grain alcohol to you brew (instead of a cleaning solution). In any event, the volumes are low enough that few people will ever be able to detect contamination should it ever occur.

Vodka is already high enough in alcohol content that it will prevent crud from growing in the airlock.

Denny Conn · Accepted Answer · 2012年9月5日 18:05

1

Denny Conn answered at 2012年9月5日 18:05

Don't bother with an airlock at that point. Just put some foil over the opening and hold it on with a rubber band. There's nothing outgassing at that point so there's no need for an airlock.

Hank · Accepted Answer · 2012年9月5日 18:01

I've had this problem. Once I cold-crashed a Better Bottle after plugging the opening with a solid stopper and the carboy puckered up. You can see the same effect if you put an opened bottle of warm soda in the fridge. I assume the air shrinks more than the liquid, but perhaps it's a combination.

It makes me a little uneasy, because once there is negative pressure in the carboy, air and contamination can slowly be drawn in. Even if you can get an airtight seal, as soon as you remove the stopper / blow-off tube, there's an inrush of air and oxygen.

My solution has been to transfer to a keg before I cold crash and slightly pressurize the keg with CO2. This has several benefits:

There is enough pressure to resist the shrinkage.
Beer is protected by CO2 for storage.
It will speed up the carbonation process later on since there will already be some CO2 in solution.

I usually pressurize to 10 psi or so and then disconnect it. After a week or so the pressure has dropped almost to zero due to shrinkage and dissolution, but that's OK. You could also just leave it hooked up to the CO2 tank and carbonate it at the same time. Aging and carbonation don't interfere with each other.

paul · Accepted Answer · 2012年9月5日 17:44

I've never had this problem. Here are some ideas:

overfill the airlock if it's a 3 piece
use a blow-off tube with a bucket
get a dry trap airlock from better bottle http://www.better-bottle.com/products_master.html

The idea that you'd get enough shrinkage to really notice it sounds dubious to me though, seems more likely that it's leaking into your carboy or evaporating.

handling shrinkage from crash cooling

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