Back when we had a teenager or two in the house, we'd drink a gallon of skim milk a day, and I never had problems with spoilage. I'd buy two gallons each trip and all was fine. Now that it's just the two of us, it takes 2 or 3 days to use a gallon. One would think I could just buy one gallon per trip and it should be ok, but I find that 2 days after opening it, I can't drink it because it has an "off" taste (I'm very sensitive). It's still way before the printed expiration date. Does milk start to spoil after you open it? Am I just a wuss? I guess I'm going to have to start buying two half gallons each trip, but it just seems silly!