Best way to crash after diacetyl rest??

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timtoos
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Best way to crash after diacetyl rest??

Post by timtoos » Fri Aug 20, 2021 5:14 pm

Cold crash and reducing O2 ingress question.

I have a lager just on diacetyl rest. Completion tomorrow and then intend to cold crash.

Its in a chronical FV and I have a glycol chiller to crash - but I am wondering the best way to crash cool and not cause oxidisation issues? If I crash what is the likely hood that enough O2 would be pulled in to cause an issue?

I also have a brite tank that I could transfer into to crash ad condition. However I ideally wanted to crash in the FV for at least 2 weeks to try and get loads of crap to drop out before brite tank racking.

What about purging the brite tank with CO2 and then connecting this to the FV? Is this just plain silly?

Advice?

TIA

McMullan

Re: Best way to crash after diacetyl rest??

Post by McMullan » Fri Aug 20, 2021 5:26 pm

The slower the better generally. You don't want to create a negative pressure inside the FV by reducing the temperature too quickly. That's going to risk damaging the FV, if it's not up to it, and sucking in air, if it's not completely sealed. A couple days at least, in my opinion. Drop the temperature a couple degrees a few times a day. This maintains sufficient residual yeast activity to counter a vacuum forming inside the FV. I think it really helps if you have a thermowell inside the FV, so when it says X℃ you know it's actually X℃. In future, purge the bright tank with CO2 produced during fermentation.

Edit: Some people might be tempted to maintain pressure in the FV, when cooling, by using CO2 while literally crashing the temperature too quickly, but it likely stresses the yeast, with a risk of the end product being comparable to mass produced crap.

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Jocky
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Re: Best way to crash after diacetyl rest??

Post by Jocky » Sat Aug 21, 2021 11:35 am

When I do a cold crash I partially fill a foil balloon with CO2 and attach it to the airlock port. This avoids any airlock suck back or oxidation issues.

If you don’t have CO2 to hand then either consider using the fermentation to fill a balloon in future, or just don’t cold crash.
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timtoos
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Re: Best way to crash after diacetyl rest??

Post by timtoos » Sun Aug 22, 2021 7:18 pm

Thanks guys, Im chilling slowly, but keeping a -ve pressure of CO2 in the FV.
Hope it comes out ok. Ive yet to brew a lager that Im happy with

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