7

If you use 2-Litres, then instead of using balloons you can tighten the cap to just before it is fully sealed, which will let gas escape when it builds up but won't let any in when it stops fermenting.

Instead of a balloon, you can use a common fermenter airlock. They cost about $1.50.

Take the balloon and poke a few holes in it using the pin. Take the cap off the bottle and stretch the balloon across the opening. Put an elastic around the balloon on the top of the bottle to hold it in position. Carefully put the bottle in a plastic bag that will catch any wine that overflows or spills. Put the bottle in your decided location and leave it there for about 2 weeks, until the balloon isn't full of gas anymore. The balloon will fill up with gas which will leak out the holes in it, but when the gas stops, the holes will close and air won’t be able to get in and ruin your wine. This process is where the alcohol is being produced, and is called fermentation.