How long can you keep dairy?
Buttermilk tastes best if used by the sell-by date on the carton, although it usually keeps two weeks past that if refrigerated properly. Beyond that, it can become too bitter to drink. Actual spoilage can appear as off-odors or as a grayish liquid on top. It can be frozen; use within a month or two for best quality.
Sour cream maintains good eating quality for two to three weeks after the sell-by date. As long as it looks and tastes all right, it's safe to eat. Sour cream should be discarded if you see mold spots, pink or green scum, or cloudy liquid on top. Freezing is not recommended because it causes separation.
Yogurt maintains good quality for one to two weeks after the sell-by date. It should be discarded if there are any signs of blue, green or pink mold. It can also develop a yeasty flavor. Yogurt can be frozen for one to two months.
Cream stays fresh for about one week after the sell-by date. Whipped cream can be frozen in dollops on wax paper and then packed in a container. Unwhipped cream also can be frozen, but the volume will be less when whipped.
Cottage cheese keeps about five days after the sell-by date. Taste is an indicator of freshness. Do not use if mold appears. Cottage cheese becomes grainy if frozen, but it's not noticeable if mixed in a dish such as lasagna.
Butter that has been opened will have the best flavor if it's stored in a covered dish and refrigerated in the butter compartment. Both opened and unopened butter may be kept on the refrigerator shelf for a month after the sell-by date. Flavor is an indication when it no longer is usable: It will develop a strong, rancid taste.
To freeze, wrap in foil or place in freezer bags. Butter keeps well four to six months at 0 degrees or lower.
Brick cream cheese should be eaten by the "best when used by" date on the package for best flavor. Once opened, don't use it if mold appears or it has a sour flavor. It can be frozen up to two months, but plan to use it for cooking, instead of as a spread, because the texture becomes crumbly. Whipped cream cheese can be frozen up to six months. Soft cream cheese does not freeze well.
Milk apparently keeps about a week after the sell by date.
The key to all of these is storage. You need to store them properly and keep them in the coldest part of your refrigerator.