Trial runs with Bag-Thing™️

Since I started fermenting under pressure with the Fermzilla I’ve been wondering how I can reduce oxygen exposure when using more traditional vessels, including the SS Brewtech mini-bucket I purchased at the same time for experimental batches. It’s got a small spigot at the base for drawing samples / transfer / bottling, but whenever you open it you invariably suck air in via the top, and that’s not ideal.

The guys over at Brulosophy have previously something they called at BrüLoonLock, which is basically a mylar balloon taped to a tube and used in place of an airlock. It’s a great idea since it allows capture of CO2 during fermentation which can then be fed back into the keg when samples are taken or during cold-crashing. I’m not sure why they went for a mylar ballon; could be that there’s no material resistance when filling up, could be that CO2 doesn’t permeate that particular material although, even if it did, I wouldn’t care since oxygen is unlikely to get in while CO2 is leaking out.

Regardless, I don’t have access to a mylar balloon right now, and with us being subject to lockdown 3.0 over here one needs to get creative. So I cut a length of plastic food-saver bag and sealed a section of 3/8″ gas line in at one end using RTV, a cross between silicone sealant and industrial glue.

Anyone seen my colostomy bag?

Using a piece of gas line allows me to slot this into the same bung which the airlock uses, and also opens up various other possibilities like pre-charging it with CO2 using a regular John Guest fitting, or including a T-piece and spunding valve in case I ever forget to remove the Bag-Thing once it’s full.

Speaking of which, I wonder what sort of pressure this will withstand? The bag’s edges are welded together and RTV sticks like the proverbial poo to a blanket, so I reckon this should handle a couple of PSI without too much bother. Finally, purging the bag of oxygen prior to use couldn’t be simpler, and that’s where I reckon I’ve got an advantage over the BrüLoonLock: just fold Bag-Thing in half and shut it in a book.

As I write this the bag is connected to my mini-bucket which is fermenting the second batch of blonde extract, and although fermentation has slowed considerably over the last 2 days there’s still enough going on to slowly fill her up. If this experiment is successful then I might make a bigger version so that I can bottle from the keg without having to top up the CO2 reserve, or I may not bother – any oxygen that’s sucked in via the top might well mix readily with the heavier-than-air ‘CO2 blanket’ sitting on top of the beer, but as I’m drawing from the bottom of the bucket and not swirling the brew around I don’t see how any oxygen exposure would have a chance to spoil any but the very last bottle, which is usually a partial fill that’s consumed early.

It’ll never fly…