Cold crashing

[Beer-lord]

Reading the Q&A in the latest Brew Your Own magazine there's a question about cold crashing a New England IPA and the answer seemed to pertain to cold crashing in general as far as making sure you have positive pressure in the fermenter before you cold crash. Well, I never do nor do I really have a way to do so. There have been times when I went from 66 to 34 to fast and the Star San was sucked into the beer but I'd never have known it.
Now I do my cold down in stages over about half a day and don't seem to get the drawn down out of the airlock. I know I'm missing something simple here as this doesn't seem to be a big deal to me. How much air could actually be pulled into the beer during cold crash to affect it by oxidation?

[mashani]

Considering that I don't airlock my fermenters / semi-open ferment, so by around day 10 or so some oxygen has displaced CO2 (as in if my brett is in there, a pellicle film will start to form around then), and I typically don't bottle until 14 days, and I can sock away the resulting beer for a year or two even and it's not oxidized and tasting like cardboard, I would think that the amount of oxidation from a cold crash is nothing to worry about unless worrying about such things is what floats your boat.

Although that said, this isn't apples to apples, as in your case your not just displacing CO2, but also allowing more of the oxygen to be absorbed into solution due to the colder temps. But if your drinking it in months instead of years, then I still can't imagine it is significant.

This will explain how to calculate "just how much" if you really want to get into the math.

http://physics.info/gas-laws/

You can find calculators if you google "gas law calculator". But you will probably need to convert F/C temps to K for many of them.

[ScrewyBrewer]

I know there's a formula, can't recall it at the moment though, that calculates the expansion of wort as its temperature goes up. Logically there must be a way to calculate how much the wort shrinks as its cooled. But truth be told I've had an ounce or two of StarSan get sucked into my 6.5 gallon fermentors and it's never hurt a thing.

[MadBrewer]

It's interesting this came up because I was just thinking about it the other day. I gave up on airlocks and blow off tubes a while back, I just cover my carboy opening with foil. In the past I have sucked up starsan from a blow off tube and the same has happened with airlocks when I have cold crashed. The time I have done so it has been only a little bit of Starsan but the last time it happened, I was cold crashing a Kolsch and I sucked up a LOT of starsan. I went with it and the beer was amazing, didn't hurt it a bit. My question has always been whats worse, some starsan or some oxygen? Starsan by itself may not be a problem but sometimes the container of starsan the blow off tube is sitting is can be pretty nasty with some yeast, trub...etc I don't really want that being sucked back in after the fact.

I have a lager going now, afer the D-rest I will be cold crashing but I think I will take it down in steps this time. Again the carboy opening only has foil on it so it will easily suck in some air. I haven't really noticed oxidation in my beers so I'm good with what I do but it doesn't hurt to do a better job if we can.

[Beer-lord]

I dropped my 2 beers from 68 to 52 in about 2 hours and nothing left the airlocks. Next I'll drop to 42 which will take about an hour and see what happens then to 34.
I do agree that with blow off tubes, this is not the best way due to all the yeast funk and who knows what else could be introduced into the fermenters but the little bit of Star San the airlock holds is so small, there's no worry.

[FrozenInTime]

When I cold crash, I drop the temp 4 degrees/day until I hit 34/35 then leave sit for 3 days. I have never noticed any airlock suction, well, to date anywayz. Not saying it can't happen, I can see where it could happen. I always use vodka in my airlock, just in case. Always good for a shot after keg'n/bottl'n.

[mashani]

It's interesting this came up because I was just thinking about it the other day. I gave up on airlocks and blow off tubes a while back, I just cover my carboy opening with foil. In the past I have sucked up starsan from a blow off tube and the same has happened with airlocks when I have cold crashed. The time I have done so it has been only a little bit of Starsan but the last time it happened, I was cold crashing a Kolsch and I sucked up a LOT of starsan. I went with it and the beer was amazing, didn't hurt it a bit. My question has always been whats worse, some starsan or some oxygen? Starsan by itself may not be a problem but sometimes the container of starsan the blow off tube is sitting is can be pretty nasty with some yeast, trub...etc I don't really want that being sucked back in after the fact.

I have a lager going now, afer the D-rest I will be cold crashing but I think I will take it down in steps this time. Again the carboy opening only has foil on it so it will easily suck in some air. I haven't really noticed oxidation in my beers so I'm good with what I do but it doesn't hurt to do a better job if we can.

It is going to suck in the same amount of air over time regardless of if you are semi-open fermenting like you and I, or if you have an airlock, because sucking in due to pressure reduction inside the container isn't what an airlock helps with (which is why if it happens too fast the airlock liquid gets sucked in, but either way, it's "bubbling" in reverse, and will continue to do so. Because... GAS LAWS. You can't defy the gas laws. That's why they are laws. LOL.

So the only way to prevent it would be to completely airtight seal your fermenter.

Which if it was made of plastic might start to "crush" it a bit if you get it really cold.

If made of glass or metal, either you make what amounts to a partial a vacuum, and then if you try to open it in that state it will go "whoosh" and suck in a lot of stuff from your air all at once, or simply implode, but I doubt that you could create enough negative pressure to implode it. But considering I once made enough positive pressure to explode a defective glass carboy, I wouldn't rule it out if your carboy had flaws/stress fracture like stuff going on. It would depend on just how cold you made it and how fast and the condition of the fermenter.

[Whamolagan]

Well that explains where all the star san in the blow off container went. So could a check valve solve that problem vs. stepping down?

[Beer-lord]

Over 18 hours I went from 68 to 34 with no loss of star san in my airlocks. Not a problem for me.
Boy does this really clear the beer and make carbing happen days faster but just looks nice going from FV to keg.