CO2 recycling system

see copyright notice. Page created 10-Oct-2009 updated 14-Oct-2010. Use the button groups above to navigate quickly around the site.

The disappearance of (old-style) SodaStream cylinders from the supermarket shelves sent my homebrew dispense system into crisis. For many years I'd relied on being able to top up the gas in the barrel, when the natural condition was exhausted, 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 I tackled was to couple some plastic tube to the screw-on barrel top, so that my stored gas could be fed in at low-ish pressure. 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 chemical in the book, I gave up and used a junior hacksaw to cut it away, then 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.

Initially, I used 22-litre polythene cubes ("polypins") to store the captured gas at more-or-less atmospheric pressure. This 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 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 both 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 didn't make a gas-tight seal, so I worked some fine grade flexible filler round the ends of the sleeve (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 was my complete recycling system. I brew roughly once a month, so I 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 discourage nasties.

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 evolved a regime in which the polypin that was connected to the dispense barrel was topped up once or twice during the new fermentation, and remained connected until the barrel was empty. The other polypin was 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. At first I tried to restore the barrel pressure by squashing the polypin with one hand, whilst turning off the barrel's gas tap with the other. This didn't really maintain enough pressure (even for a real ale drinker!) so I've now added a small multi-purpose pump (from Betterware) in the gas line to the barrel. This has the added advantage that one can completely empty the gas reservoir into the barrel.

The pump fittings are quite wide, but I found that a short length of the supplied tube reduced the diameter to make a good push-fit for my trusty inline taps. The pump delivers about 70ml per stroke, so 10-12 strokes restore the pressure after serving a pint; it's about right when the pump handle rises slightly by itself after the downstroke.

This pumped system uses more gas, so I've adapted two more containers as reservoirs. This time they are 20-litre collapsible water carriers, intended for camping, with taps that are smaller than the polypin ones, and lack that annoying anti-drip hole. So I've just pushed the inline valve spigots into the tap nozzles. It works, but I suspect the very soft plastic from which the water carriers are made makes them less suitable than polypins for gas storage.

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