I semi-regularly brew kvass, a [delicious] low alcohol content carbonated probiotic drink, and it's quite similar to beer:
- Toast 300g sliced [rye] bread to near burning
- Boil 3 liters of water, turn off, insert/soak bread
- Let sit covered for 6 hours
- Add 150g sugar, 6g instant yeast
- Let sit covered for 18 hours
- Remove bread, strain out extra liquid from it. Birds love it, once it dries out.
- Bottle up the liquid (leave headspace for gassing), and occasionally burp it.
- Wait. Longer bottling period = smoother, less carbonated, more alcohol, less sweet. ~12 hours, but this is very subjective.
- Chill + drink. Take the lid off very carefully, aim away from eyes.