I'm sure by now every one is familiar with Pat's Backcountry Beverages Brew Concentrate (and if you're not, you reeeelly should be!). Which means you're also familiar with their carbonator. It looks something light a mutant Nalgene bottle, weighs 10oz and consumes a packet of fizzy powder weighing about a half ounce for each pint of beer you make. To make 5 beers, it'll start out at 12.5oz and drop to 10oz.
I figured out how to cobble together a carbonator weighing just 2.5oz consuming 3g of C02 for each pint, with an overhead of 1.5oz for the empty C02 cartridge which is good for 5 beers. To make 5 beers it'll start out at 4.5oz and drop to 4oz.
If you're on the trail long enough, Pat's carbonator will be lighter in ounces/day, but if, like any sane person carrying beer in to the back country, you drink a pint a day, that point is well past a week in the woods.
Here's how to make one…
Materials:
– one 16oz – 18oz plastic carbonated beverage bottle
– two Presta valves from bicycle tubes, threaded with lock rings
– one additional Presta valve lock ring
– one suitable spring (mine was from the random bike parts bin)
– one paper clip
– one C02 bicycle tire inflator (these can weigh as little as a 0.5oz)
Tools:
– scissors
– needle nose pliers w/ wire cutter
– drill
I think the photos are fairly self explanatory, so rather than give detailed assembly instructions I'll explain what to watch out for and how to get it to actually work.
(Now would be a good time to scroll down and look over the photos so you'll know what I'm talking about.)
It's simple enough to stick a valve on a plastic cap, but that's not the safest arrangement when you're pressurizing your bottle w/ a compressed gas cartridge. That's where the second valve, on the inside of the cap comes in. It's a pressure relief valve. That spring holds the valve in the closed position (up) in spite of a high pressure inside the bottle trying to force it open (push the pin down). That second lock ring is used to adjust the spring tension – it's not tightened down against the other one. This effectively adjusts the blow-off pressure; the pressure at which the valve will open and allow gas to escape rather than building up.
To calibrate the blow off pressure, I used a bicycle pump with a pressure gauge on it. I settled on 50psi (TEST YOUR BOTTLE FIRST! See safety tips below). To carbonate, pressurize the bottle until the blow off valve releases and then closes, then shake vigorously until you feel the pressure stabilize (30 – 60 seconds). You will definitely notice the pressure dropping as you shake and the gas goes in to solution in the water. Repeating this 3 times produces a suitable degree of carbonation for beer.
Things to watch out for:
– be sure you place the holes in the cap such that you can securely install both valves with their lock rings and still close the cap on the bottle completely
– verify that the pin on the relief valve is lifted fully up (closed) by the spring and that it can still move down (open) unobstructed.
– coming up w/ a good way to couple the spring to the valve pin w/ a piece of bent paper clip and installing it against the compressed spring can be tricky!
– when carbonating, apply pressure to the inflator ***SLOWLY*** There's a bit of a learning curve to this.
Some important health and safety tips:
Bicycle parts ARE NOT FOOD SAFE. I have no idea what sort of nasty chemicals might leach out of a valve that you WASH THOROUGHLY WITH WARM SOAPY WATER but if it'll save me a half pound in the name of a cold beer at the end of a hot trail, I'm prepared to live with it (and you should be too!).
USE FOOD SAFE C02. I think this is far more important than what might be imparted by the valves. Unlike the valves, you're actually consuming the gas. Food safe C02 cartridges are readily available on-line and wind up costing in the neighborhood of $0.50 a beer. I don't think non-food safe cartridges cost any less.
Verify your bottle strength. Not all bottles are created equal. A ruptured bottle can cause injury. Use a blow-off pressure several times lower than your maximum test pressure.
Above all, use caution and common sense any time you are working with compressed gas. Go slow, stop and think. Use hearing and eye protection when conducting tests, and do so in a safe place. Once tested, assembled and tested some more, this system has proven reliable and easy to use and has given me no cause for alarm. I've carbonated ~20 bottles of water with it so far.
Cheers,
-Rene
Images:
All pieces, fully disassembled
Partial assembly showing relief valve put together (they have to be taken apart to be installed)
Relief valve installed in cap
Fully assembled carbonator cap
Relief valve detail
Tire inflator installed on a 16g food grade C02 cartridge
