Build your own soda maker

It’s now running for several years and it keeps going well. If you enjoy your own soda, seltzer, Sprudel, … here is a truly low-cost solution. There’s a bit of initial investment, but it’s paid off in a few months and from there on, you make your drinks at a fraction the cost you’d buy them from your favourite soft-drink conglomerate. More, you won’t have to carry the heavy bottles home — just use tap water instead. Just use a filter if your local water a bit questionable.

The set-up is simply a CO2 tank and a regulator which brings the pressure down from ~70bars to ~3bars. All the equipment was purchased in an aquarium shop — the fish lovers use this kind of equipment to inject CO2 into their fish tanks to help plant growth. Go to your local aquarium store or search online, all is readily available.

If you can, get a regulator which has a pressure-adjustable output. You get the best and quickest soda at around 3-4 bars, but non-adjustable regs deliver ~2 bars, which essentially means that it takes you a bit longer to make your drinks.

Then, here’s how it works: The reg transforms your CO2 tank pressure down to a manageable 2-4 bars. It usually then passes through a solenoid, which is nothing more than an electrically controlled on/off valve. You don’t really need this, but many regs have it attached anyhow. If you don’t have this solenoid, never mind. just operate your tank switch instead.

Next in the chain is a needle valve. This is totally useless for your task — aquarists use it to control the amount of CO2 flowing into their tank. They want a constant but slow dissipation of CO2. We want as much CO2 as quickly as possible instead. So for our job, simply open the needle valve fully or better yet, remove it completely.

The CO2 then goes into the hose (which, again, comes from the aquarium shop).

Finally, the hose ends in a bottle cap. You make the drinks in PET bottles which can withstand the pressure. All kinds of Coke, Sprite, Fanta, … bottles are an excellent choice for this. Their caps are standardized, even for bottles of different sizes.

To connect the cap to the hose, there are a few different methods which have been practically verified by now:

  • As shown on the picture, use a plastic hose connector from a little thingy you got from the aquarium shop (such as a reverse-block valve). These things cost close to nothing. Drill a hole into the bottle cap and push the thing in from the back. Depending on the fit, you might have to glue it in to get it resist the pressure. The one shown on the picture actually lives without glue.
  • Use a valve from a bicycle. Don’t go for a thick valve (called Schrader, the same that is used for a car) but the good old standard type (called Presta). These valves are screwed to the rim with a bolt. Just remove the inside (valvy thing) of the valve and use two bolts, one at the inside and one at the outside of the cap to hold it in place. The standard aquarium hose fits right over this thing and holds tight.
  • Get a plumbing hose connector with a matching bolt and screw a normal bottle cap in-between the connector and the bolt. You will need a thicker diameter hose for this and some sort of connector on the regulator side. While being more effort, you will have the advantage of higher CO2 flow, ergo faster drink-preparation.
  • Ask your favourite machinist to make a dedicated cap with connector for you.

Once the cap is sorted out, you’re ready to roll:

  • Always use cold water to make your soda. The lower the temperature of the water, the more CO2 it will dissolve. You will want to be as close to the freezing point of water as possible to get a lot of CO2 in quickly…
  • Shake the bottle well while pressurized. When you wildly break the surface of the water, a lot more CO2 is dissolved into the water. Leaving the bottle “idle” will probably take hours to get your soda done, shaking it wildly reduces this time to seconds…
  • Never fully fill your bottle. You will want some air-space in your bottle so that you have a surface of water which will interface with the CO2. If the bottle is completely filled, it’ll be very very hard to get CO2 into the water
  • Don’t use glass bottles. Never ever! While they might withstand the pressure, the results could be horrible if they do not hold…
  • Only use PET bottles which contained fizzy drinks. Don’t use bottles which contained flat drinks, they might not be able to withstand pressure!
  • Don’t fill the bottles with very hot liquid. They would be deformed, likely weakening the structure.
  • Don’t pressurize bottles while they’re not full of liquid. For one, you’ll lose a lot of CO2 if you do that. Even worse, the gas in the bottle will get compressed a lot. If something ruptures, the compressed gas contains a lot of energy and results might be serious. Liquid, on the other hand, is almost incompressible, I.e. it contains far less energy to blast things around.