johnr's CO2 recycling system

Carbon Dioxide Recycling
Capture and store from fermentation, re-use for dispense

see copyright notice. Page created 10-Oct-2009

The story so far

The disappearance of SodaStream cylinders from the supermarket shelves last year sent my homebrew dispense system into crisis. For many years I've relied on being able to top up the gas in the barrel, if the natural condition falls off, using this simple but highly effective manual injector made by Boots. In truth, the O-rings in the barrel fitting were starting to leak, and I knew I'd have to replace the system soon. But suddenly I found myself having to do some quick thinking!

I'm actually rather glad I was forced to develop a new system, because the old one wasn't exactly Green. Venting all that carbon dioxide (of all things!) from my brew into the atmosphere, and then replacing it with someone else's, compressed and transported, at great expense of energy, to my house - I should have moved away from that approach years ago!

The first job was to couple some plastic tube to the barrel through the screw-on top. This meant removing the aluminium injector fitting, which wasn't easy, as corrosion had turned the threaded part and its back nut into a single, immovable entity! After trying every solvent in the book, I gave up and used a junior hacksaw to cut it away, and re-fitted the rubber blanking plug that came with the barrel.

I drilled a 7mm hole in the blanking plug to accept the long spigot of a plastic inline tap. Although these are intended for use with liquids (in beer lines), they've proved to be fairly gas-tight, and provide a neat way to isolate the various parts of the system. There's slight leakage in the "off" position, but it's not a problem when both sides are at a similar pressure. The fitting of the tube to the other spigot is improved by smoothing down the welded seam that runs along the latter (with a sharp modelling knife), and stretching a couple of turns of self-amalgamating silicone tape round the tube like an elastic band.

My system uses large polythene cubes ("polypins") to store the captured gas. It works best with the modern design of polypin, which is lighter and easier to collapse (as shown in the photo) than the semi-rigid ones from the 1980s. I've removed the tap insert and handle, and threaded a short length of tubing through the outer sleeve of the tap, with an elliptical hole cut in the tube so that it lines up with the one on the inside of the sleeve. This arrangement provides dual-port access via taps at the ends of the tube, so that the reservoir in use for dispense can be topped-up from a new fermentation without disconnecting anything.

The tube I used was a loose fit in the sleeve, so I wound a few turns of PTFE tape either side of the hole to make it a push fit. This in itself does not give a gas-tight seal, so I've been trying various glues and fillers applied round each end of the sleeve. So far a fine grade flexible filler has been the most successful (silicone sealants are no good because they don't "stick" to polythene). It's also necessary to fill the small anti-drip hole on the outside of the sleeve, and a smear of filler round the edges of the lined-up elliptical holes helps to make a secondary seal. Again, silicone tape is useful to keep everything tight.

Tap spigots without any tube attached need to be capped to reduce leakage. I found various push-on caps in the junk box, including some from the ends of an old TV aerial, and some used to seal co-axial cable supplied in bulk on drums. Never, ever throw stuff like that away!

The source of CO2 is, of course, a fermenting bin. There was already a small hole in the lid of this one, which I enlarged to 3/8 inch with a Q-Max cutter. Designed for punching holes in sheet metal, I thought I detected a snort of indignation when I applied it to polypropylene, but it worked just fine.

Another rummage through the junk box produced a sleeved grommet that pushed neatly into the end of my plastic tube, but the grommet bit was designed for something thicker than my bin lid. So I padded it out with a suitable O-ring, which you can't see because it's on the inside face of the lid.

So this is the complete recycling system. I brew roughly once a month, and have adapted two polypins as gas reservoirs to go with my two barrels. They need to be fully collapsed before initial filling, and if time permits I like to fill and empty them a couple of times to make sure there's as little air as possible diluting the CO2. Likewise, the tube should be flushed through by the flow from the fermenter before it's connected to the polypin. Polypins and tubes need to be washed occasionally and rinsed with metabisulphite solution, to maintain sterility.

It takes between 2 and 6 hours to collect 20 litres of gas, and you need to be ready to disconnect the tube when the fermenter lid starts to bulge, although I think it's designed to self-vent if the pressure gets really high. I've evolved a regime in which the polypin that's connected to the current barrel is topped up once or twice during the new fermentation, and remains connected until the barrel is empty. The other polypin is emptied and refilled during the same fermentation, ready for use with the next barrel.

After initial priming (if necessary) and conditioning, the barrel's gas tap can be left "off" until enough beer has been drawn off to exhaust the pressure. Thereafter, the taps between polypin and barrel must be opened to dispense beer. Barrel pressure is restored by squashing the polypin with one hand, whilst turning off the barrel's gas tap with the other. Provided the beer is kept cool at all times, it retains enough condition right to the end. Enough, that is, for a real ale drinker. It wouldn't suit kegheads!

To be continued

Carbon Dioxide Recycling Capture and store from fermentation, re-use for dispense

The story so far

To be continued

Carbon Dioxide Recycling
Capture and store from fermentation, re-use for dispense