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Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > Temp reduction suckback - Let's brainstorm
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Old 12-19-2009, 02:09 AM   #1
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Default Temp reduction suckback - Let's brainstorm

Maybe some folks have this all figured out and perhaps many others don't even know it's an issue. When you ferment at one temp and then reduce the temp later for any reason, you reduce the pressure in the fermenter pretty significantly. This can be trouble when cold crashing an ale or when ramping a lager down to 35 down from a diacytel rest.

If you use a bubbler airlock, you are certainly sucking the liquid in. If you use a medium sized blowoff into some liquid, you can definitely suck that back in too. My fermenting fridge isn't exactly a spotless sanctuary and I don't like the idea of that air nor oxygen getting into the fermenter.

My initial idea is to fill a plastic bag with CO2 and rubberband it over the blowoff tube (the end that is normally sitting in the starsan bucket). I'd do this right when I start dropping the temp. If I anticipate it properly, an alternative is to attach a deflated bag over the carboy neck as fermentation is still happening but winding down so that it fills with "free" co2 to be sucked back in during crashing.

Discuss.

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Old 12-19-2009, 02:31 AM   #2
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Well two off the top of the head an easy one (space allowing) would be a couple coils of extra tube in a blow off, more for glass carboys that wont dent under the negative pressure. The math eludes me at the moment but I'm sure there could be a calculated amount that would allow for a draw, but not all the way back to the brew.

The other, which would work more for plastic/bettle bottles would be to attach a co2 cartridge injector near the top of the vessel and when the tempature drops to the point where negative pressure is apparent to open the valve and equalize it with a pure gas.

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Old 12-19-2009, 02:33 AM   #3
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Fill your airlock w/vodka, and don't worry about the suckback. IMHO it's not enough of a concern, any oxygen that gets sucked in should rest above the blanket of CO2 that's on top of the beer right? And any aeration/oxidation that could possibly happen from the vodka splashing in to the beer would certainly be minimal.

Just my initial thoughts...

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Old 12-19-2009, 02:47 AM   #4
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What about some kind of check valve?

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Old 12-19-2009, 02:50 AM   #5
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IMHO it's not enough of a concern, any oxygen that gets sucked in should rest above the blanket of CO2 that's on top of the beer right?
for a split second, yes. But, the laws of gas exchange would dictate that the CO2 and O2 would mix evenly.

Interesting discussion point Bobby. I'd obviously thought of the liquid that's getting sucked back (no biggee with vodka), but didn't consider the air exchange.
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Old 12-19-2009, 02:50 AM   #6
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Fill your airlock w/vodka, and don't worry about the suckback. IMHO it's not enough of a concern, any oxygen that gets sucked in should rest above the blanket of CO2 that's on top of the beer right? And any aeration/oxidation that could possibly happen from the vodka splashing in to the beer would certainly be minimal.

Just my initial thoughts...
I completely agree. Who cares? What is the issue Bobby? Are you worried about contamination or off flavors...it would seem that .5 ounces in 5 gallons is literally "a drop in the bucket."
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Old 12-19-2009, 02:57 AM   #7
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I think the concern is the propensity for oxidation.

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Old 12-19-2009, 03:02 AM   #8
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Some kind of on demand valve from your CO2 tank, not sure how but someone on HBT will figure it out or already does it.

Personally I am still waiting for the one button CIP solution (Kladue).

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Old 12-19-2009, 03:17 AM   #9
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Default Foil

My vote is to bag the airlock all together prior to cold crash and cover it with sanitized foil. I don't really want vodka in my beer, and unless you're moving it around I wouldn't think the tiny bit of O2 would penetrate the cozy CO2 blanket mentioned above.

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Old 12-19-2009, 03:19 AM   #10
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Slap a "jimmy" on your hose before putting it in the "box".

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