Start by bringing one gallon of milk to just under a boil (about 190F or so). Pour in 1/2 cup of vinegar (distilled white is best, red wine or cider will probably make it taste funky), and let the mixture cool. You can add salt if you like, but that's optional. Once the mixture (curds and whey) is cool, you can strain off the whey in a colander or cheese cloth, and viola! Homemade cottage cheese. The curds form from the vinegar, which is basically acetic acid, which takes the place of lactic acid produced by cheesy bacteria in their fermentation process.