Fermenting with corny kegs - purging oxygen

[Dr Jacoby]

(Warning: long post!)

I ferment in corny kegs and then push the beer under pressure to a receiving keg to serve or dry hop or whatever. One of the issues I've been concerned about is ensuring that the receiving corny is completely oxygen free (or as close to free as I can get it) prior to transfer. My technique up to this point has been to double purge the receiving keg (i.e. fill it with Co2, purge from the valve on top, repeat and then pressurise to just under 5 psi).

I brewed a beer recently that required numerous transfers and it ended up badly oxidised, even though I carried out this procedure for each transfer. I looked into it and discovered that pro breweries often use a very specific technique for purging their brite tanks (or any other tank that the beer touches post fermentation). The idea is to gently push Co2 in through the bottom of the vessel (no more than 5psi) and slowly bleed excess gas from the top. It takes a while but this will eventually dilute the oxygen to negligible levels.

My technique wasn't working very effectively because I was forcing the Co2 into the corny at a higher pressure and then venting in one go. In effect, I was diluting the oxygen but not very efficiently.

Lots of people cite the fact that oxygen is lighter than Co2, so by venting at the top of a keg more oxygen should be released than Co2. The reality is not so straightforward. Oxygen and Co2 mix very easily so you don't really get a blanket of Co2 neatly divided from the oxygen. The best we can do in the real world is to use a technique that dilutes the oxygen levels as efficiently as possible - unfortunately, this requires carrying out something like the procedure outlined above that breweries often use. Applying this to a corny keg, it would require gently forcing Co2 in through the liquid disconnect and gently bleeding gas from the valve on top (or through a bleed valve on the gas out post). This is likely to be time consuming and use up a lot of Co2. 

So I started thinking about a way around this and came up with the following. Instead of installing a blow off tube to the corny during fermentation, I could use a jumper lead to connect this corny to a sanitised receiving corny (gas out to liquid in would work best). Then put a bleed valve or a blow off tube on the receiving keg. The Co2 produced by the yeast during fermentation could then be used to purge the receiving keg over the course of fermentation. Any unwanted gases produced during the initial stages of fermentation would be bled away so that by the end of fermentation the receiving keg would contain reasonably pure C02. When the fermented beer is then transferred into this keg it would push out most of the remaining gas and you could burp the keg a few times to ensure the headspace is more or less filled with fresh Co2 from the bottle. You could even purge multiple kegs over the course of fermentation if you wanted. There would be more than enough gas produced I reckon.

This method seems to have the following benefits:

1. Oxygen would be completely purged from the receiving keg (I can't see how any would be left over after 8+ days of fermentation pressure).
2. You would use far less Co2 from your bottle.

Have I missed anything? Is there an obvious downside to this method?       

[Ciderhead]

Pictures tell a thousand words it also helps when you can't read joined up writing.

[Eugene O'Brien]

Why not fill corney with liquid to displace all the air. Gently blow it out with co2. Job done!

Sent from my GT-S5570 using Tapatalk 2

[Dr Jacoby]

That's a good idea but I had already discounted it because I cut my dip tubes back to allow me to ferment in the cornies and to help with clarification during transfers.

[Will_D]

That's a good idea but I had already discounted it because I cut my dip tubes back to allow me to ferment in the cornies and to help with clarification during transfers.

Surely you can swap dip tubes around:

Short for fermenting and long for dispensing.

[Dr Jacoby]

I could but I've found that you get brilliantly clear beers if you chill at 0C for a few days and serve with a shortened dip tube. Plus, if I decide to dry hop it's very useful to have the shortened dip tubes. I want the best of both worlds, oxygen free kegs and clear beer 

[Sorcerers Apprentice]

Sounds like a good plan,I would suggest venting to atmosphere until the heavy fobbing stage is over, as the CO2 will not be clean and will carry some O2 and fob with it initially. Then collect the CO2 in the second corny. Regarding O2 pick up, I would test the keg fittings, disconnects, pipework and corny lid seals for leaks as this is probably more likely to be the source of oxygen ingression, particularly as you said that you had a number of transfers and picked up O2 in the process. when the system is pressurised, apply some soapy water around all joints, pipework, lids etc and check for bubbles to indicate a leak, if gas can escape then it will also be drawn in during the transfer.

[Dr Jacoby]

Thanks for the suggestions. I'm pretty careful to check for leaks. I don't think that's the problem here.

[Dr Jacoby]

I just brewed a special bitter so I'm gonna use the opportunity to try this technique. I've attached a blow off tube to each of my corny fermenters on the gas posts (as I normally do - I use two half full cornies to accomodate krausen). When the blow off tubes shows signs of active fermentation I'll connect one of the cornies to an empty corny with a jumper lead (gas out to liquid in). I'll then switch the blow off tube to the gas post on the receiving keg to vent the Co2. It's actually a very simple procedure, it just sounds complicated when described (a bit like trying to describe how to tie shoe laces

I'll give updates on my progress.   

[Sorcerers Apprentice]

Are you using a Spunding Valve to maintain pressure?

[Sorcerers Apprentice]

Here's a video of a guy purging oxygen out of a corney by filling it with water first, then driving the water out with co2 .
http://www.youtube.com/watch?v=U9HWIFwnUK4

[Dr Jacoby]

Are you using a Spunding Valve to maintain pressure?

I ordered one yesterday as it happens. I'll only need it near the end of fermentation so hopefully it'll arrive on time.

[Sorcerers Apprentice]

Where did you get it can I ask? I was hunting for one myself

[johnrm]

I spotted them here...
https://www.hopandgrape.co.uk/beer/beer-equipment/kegs-and-barrels/cornelius-draught-system/adjustable-pressure-release-valve-gauge-for-cornelius.html
I'm curious to see if there is another source.

[Dr Jacoby]

I got mine in Hop & Grape