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CO2 Introduction Advice Solicited

mr_beer

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This is not a BIAB question per se but I decided to post here.

Headspace with oxygen is the enemy for longer secondary and tertiary fermentation -- beer, wine, mead, etc.  I want to introduce a blanket of CO2 into the carboy to occupy the headspace and provide an oxygen barrier usng a CO2 tank.  Picture the larger neck hole in the carboy and a siphon hose connected to the CO2 tank.  Open the valve and CO2 goes in and in theory the oxygen is pushed out of the empty space in the neck.  When the headspace has been purged, install a bung with airlock.  Since the CO2 is heavier than the oxygen it should provide a blanket of protection. 

So now the question -- what pressure and how long should a purge cycle be for a carboy with reasonable headspace -- 30 seconds, minute,??

Opinions and recommendations are solicited. 
 

PeeBee

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Bit late, but for what it's worth:

That CO2 is heavier than air is very true but it can be misleading. CO2 is also highly miscible with air and won't stay separate for long. Don't think oil and water, more cream on top of an "Irish coffee" and the care needed to keep those separate. Once mixed it won't separate again.

So, low pressure (you don't want a turbulent flow of gas) and not long, 30 seconds will probably be ample. Think of a bottle of same volume full of water and upside down in a bath of water - how long would it take for the gas to displace the water in the bottle? Not long. And no need to be precise, the yeast (having been starved of oxygen for some while) will quickly scavenge any remaining oxygen and stash it away "for later".
 

dtapke

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use a flowmeter on your co2 hose, i would purge 1.5X the volume of the vessel.

https://www.amazon.com/Oxygen-Measures-0-8LPM-Tinas-Homecare/dp/B001QMEG9W
 

PeeBee

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dtapke said:
use a flowmeter on your co2 hose, i would purge 1.5X the volume of the vessel.

https://www.amazon.com/Oxygen-Measures-0-8LPM-Tinas-Homecare/dp/B001QMEG9W
Excellent idea. And doesn't involve getting wet in the bath. Takes the guess work out (e.g. 2L headspace, give it a minute at 3L per minute).
 
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