I've been getting "untreated" milk, as I like to call it, for about 2 years now. It usually tastes a little sour if it has been allowed to get warm for some time. It won't hurt you. The best way to keep it tasting sweet is to keep it cold! Don't take it out of the fridge and let it sit on the counter; keep it in the back (coldest part) of your fridge; and keep it in a cooler with ice when you pick it up from your farm. I have found that my milk will stay sweet for almost two weeks if I do this. Also, keeping it in glass is best and don't open the other containers until you've finished one. Hope that helps some! Leaving it out to make whey as one wrote in above is great also for the leftover cheese! I love the cheese. It's the raw milk version of the "Whey and Cream Cheese" recipe in NT. :)