- 1/4" O.D. plastic tubing (ice-maker tubing)
- a 1.5L soda bottle
- one or more 500 mL soda bottles
- an inline valve for 1/4" plastic tubing
- two 1/4" tube to 3/8" M adapters
- two 3/8" F couplers
- Teflon tape
- active dry yeast
Standard Disclaimer: Not liable for damages due to use or misuse. No warranties expressed or implied. For educational purposes only. Safety goggles may be required during use. Some belching may occur.
Step 1: Making the Connecting Tube
The connecting tube consists of two soda bottle caps, tubing and an inline valve.
Assembly is pretty straightforward. Most of the connections are "quick-connect". No special tools required.
To attach the caps:
1. drill holes just large enough for the adapters
2. wrap the threads of the adapters with Teflon tape
3. use the couplers to tighten the adapter onto the cap
Note: I used brass couplers. I would've preferred plastic ones but couldn't find any.
Step 2: Brewing Some CO2
Fill the 1.5L bottle halfway with warm water. Add sugar and yeast. Proportions aren't critical. I used roughly a cup of sugar and a tablespoon of yeast. Mix thoroughly.
Close the valve on the connecting tube. Attach one end to the 1.5L bottle but don't fully tighten it yet.
Squeeze as much air as possible out of the bottle, then tighten the cap. This will ensure that most of the gas you end up with is CO2.
Wait. It'll take hours for the CO2 to build up to a decent pressure. The bottle will eventually expand and become firm.
Note: There's a chance that the connecting tube will leak or pop apart. If you leave the bottle too long, it could explode. Both of these are potentially very messy.
Step 3: Filling a Bottle
Take a 500mL bottle and fill it 3/4 full with cold water. Attach it to the free end of the connecting tube but don't tighten it fully.
Squeeze the air out and tighten the cap.
Open the valve. The bottle will expand and pressurize.
Shake the 500mL bottle to dissolve the CO2 in the water.
Close the valve and remove the cap.
You should now have a bottle of carbonated water. You can either drink it right away or cap it and store it in the fridge for later. Depending on how much pressure you've built up, you might be able to fill several bottles.
Note: Shaking the 1.5L bottle will help increase the pressure but take care not to get any of the yeast water in the tubing. It'll mess up the taste of the water.
The liquid doesn't have to be water. You can use orange juice and make orange soda. Or maybe some vanilla and sugar to make creme soda.
I'm not sure how renewable the CO2 source is. Presumably, you can just keep feeding the yeast sugar to make more CO2. I suspect, though, that the yeast will eventually die and you'll need to start a new batch.
Step 4: Pressure Gauge
If you're feeling ambitious, you can add a T connector and a pressure gauge. I found that 30 psi is about right for filling a bottle. I'm not sure how much pressure this setup can contain. I may have to push it to the point of failure just to find out.
Update: The highest pressure I've managed so far is 70 psi.
My current rig has two yeast bottles, each with its own valve, and a master valve. This allows me to switch out one of the bottles while maintaining the pressure.