CO2 purging

All of my sour mashes have been 3-ish gallon batches, so I usually do the extended mash in a small 5 gallon brewpot. I mix the unmilled grain, cover with lid and crimp tin foil over the edges before I lift an edge just to get the CO2 hose in there. I turn on the gas until I see the cloudy haze exiting around the CO2 hose then crimp the foil back down to completely seal it up.

After that I do not touch the lid, peek at the mash or otherwise mess with it aside from temperature adjustments to keep it in the 120s. Letting that sit for 3 days or so will be nice and tart.

 

After my kegs are cleaned before use, they are stored with 1-2 gallons of sanitized water at about 15 psi. When ready to rack, I use CO2 to empty the water through the out post (~1 min). I am sure there is still some air molecules hanging around but the process of racking forces all gas out except the last 1(?) inch of headspace. Then a couple of "burbs" to finish the job. If you really want to make a keg O2 free, fill it completely with water and force out with CO2. I think that's overkill, but it will work.

My carboy is seeing less use now that I'm kegging. I only purge the headspace with CO2, just a 10 second squirt at the top of the liquid. My estimate to purge a 5 gallon'er completely would be 1-2 minutes (at 5-8 psi), filling from the bottom.

When bottling I give each bottle 'bout 3-4 seconds pre-fill, then another 2-3 seconds in the headspace.

And I'm glad carbon dioxide is colorless . . . otherwise our pale ale would not be so pale . . .

 

My process for purging kegs is this. After cleaning and sanitizing, I fill the keg with 10-12 psi of CO2. I let it sit a few minutes (at minimum) to allow the CO2 to fall to the bottom. I purge from the top, and refill with CO2, allow that to settle for a few minutes and then purge from the top once more. And then fill one final time with CO2 and then store or use. When you open the keg after this process you do see the white hazy gas.

 

I purge my kegs by putting StarSan into the keg, closing up, shaking it all over, letting settle, then forcing out my cobra tap to sanitize the inside of the dip tube. Nice and hazy inside when I pop the top to fill. But I am still learning as I just started kegging early this year.

 

if purging a fermenter, i'll usually let it run for ~5 seconds or so on a low psi setting, like 3-5psi. Just looking for a blanket as you move the wort underneath it, you don't need to fill the whole fermenter with CO2.

For berlinerweisse, I've set it up so that I will give a quick shot of CO2 via laminar flow across the top of the grain bed every couple hours when I think about it...kind of like frequency of swirling a yeast starter without a stir plate.

 

Does the CO2 'fall' sufficiently to make a difference in only a few minutes? I just assumed that the CO2 dilutes the air that is in the keg.

Here's my take on it. I don't know the exact numbers, so I'll make some assumptions. The concept should be clear, even if the numbers are wrong, so bear with me.

Let's assume that 20psi will give us 5 volumes of gas in the keg (a big assumption, I know). If we add 20 psi of CO2 to the keg, this will blend with the O2-laden air that is already there, resulting in a 4:1 ratio of CO2 to air (80% CO2, 20% air). When you release this mixture, you end up with a keg with only 20% the original quantity of air. Do it a second time to get rid of 80% of that 20%, leaving you with 4%. Third time yields .8%, ... Each iteration reduces the remaining air by another 80%. Repeat until you've gotten down to an acceptable level of air in the keg. Clearly, you're exhausting a lot of CO2 this way, but if you're purging headspace, your options are limited. An empty vessel can be purged much more efficiently by filling it with water, then dispensing it with CO2, as PortLargo suggested.

If the CO2 does, indeed, 'fall' sufficiently, then it's possible to purge virtually all of the 'bad' air from the vessel using your technique.

 

Air is about 20% O2. If you fill to 30 Psi, purge, and repeat 2 more times you get down to about .02% O2.

Mike has the logic laid out. 30 just gives a smaller fraction each step.

 

You remember chemistry class? CO2 gas falls in a hurry...or is that just because dry ice vapors are so cold?

 

I recall working in a restaurant many years ago. To pass the time, we would occasionally fill balloons from the co2 tank in the store room. I seem to recall they would bounce quite readily when dropped.

 

awesome, place a chunk on top of the mash and you're good to go!