If unopened, whole milk lasts 5-7 days, reduced-fat and skim milk last 7 days and non-fat and lactose-free milk last 7-10 days past its printed date, if refrigerated. Milk can be refrigerated seven days; buttermilk, about two weeks. Milk or buttermilk may be frozen for about three months.
Yogurt can be stored in the refrigerator (40 ºF) one to two weeks or frozen (0 ºF) for one to two months. Soft cheeses such as cottage cheese, ricotta or Brie can be refrigerated one week but they don't freeze well. Hard cheeses such as cheddar, Swiss and Parmesan can be stored in the refrigerator six months before opening the package and three to four weeks after opening. It can also be frozen six months.
Processed cheese slices don't freeze well but can be kept in the refrigerator one to two months. Sour cream is safe in the refrigerator about one to three weeks but doesn't freeze well.
FDA supports efforts by the food industry to make “Best if Used By” the standard phrase to indicate the date when a product will be at its best flavor and quality. Consumers should examine foods for signs of spoilage that are past their “Best if used by” date. If the products have changed noticeably in color, consistency or texture, consumers may want to avoid eating them.
For more information, you may call the FDA toll-free at 888-723-3366 or go to FDA's website.