Microbus Brewery: CO2 Reservoir For Cold Crashing

Today I have a quick little write-up about my CO2 reservoir that I've been using. I got the idea from a kit sold by Brewhardware.com which may have been inspired by a Brulosophy post...I'm really not sure which one of these two came first, but I saw the Brewhardware kit first. The concept is simple, in order to minimize oxygen exposure (e.g. via suck back), employ a reservoir filled with CO2 so that as the finished beer cools and the gas reduces in volume, CO2 is drawn into the fermenter rather than air. As most brewers know, oxygen + finished beer = stale oxidized flavors and aromas, muted hop character, etc.

My first test setup utilized a mylar balloon for the reservoir as described in the Brulosophy post. Mine consisted of a balloon, a small piece of 1/2" stainless tubing jammed into balloon's valve, then this assembly was filled with CO2 and inserted into the fermenter bung. It worked great, but since I couldn't see inside the mylar balloon to make sure it was clean, I started to worry about the potential for infections with re-use. Mylar balloons are cheap, but I didn't want to add one to the landfill every time I brewed a new beer.

This led to my slightly improved second iteration which involved a water bladder I purchased through Amazon. The bladder is similar to Camelbak bladders except it has a slide lock that I can use to access the interior. I also replaced the 1/2" stainless tubing with a 3/8" stainless barbed elbow (because these fit better in the bung). This setup worked well and the only problem was when it was time to transfer to keg, I had to disconnect the reservoir, then connect low pressure CO2 to complete the transfer. Depending on how much CO2 was left in the reservoir, there was the potential to introduce some oxygen when swapping out the reservoir for the CO2 line. Also, I found it hard to maintain constant low pressure CO2 flowing into the fermenter as the beer filled the keg.

Enter version 3 of my CO2 reservoir, and what I think will probably be the final iteration. For this version, I swapped the 3/8" barbed elbow for a 3/8" barbed tee. One barbed port gets inserted into the bung, the bladder is attached to another, and a valved disconnect is attached to the third. This allows me to fill or re-fill the reservoir via the valved disconnect whenever the reservoir is running low. I can also fill it as I'm transferring to keg, eliminating the risk of over-pressurizing the fermenter.

Here are a list of parts I used for my build: