You bought a quart of buttermilk, used what you needed for a recipe, and put it back on the fridge door. Or maybe you picked up a canister of buttermilk powder at the store and are wondering whether you should keep it in the fridge, too. The answer depends on which product you have. Does buttermilk need to be refrigerated?
Does buttermilk need to be refrigerated?
Short answer: Carton buttermilk must be refrigerated at all times. It is a perishable dairy product that requires continuous cold storage at or below 40 degrees Fahrenheit, whether opened or not.
Buttermilk powder is different: It is shelf-stable and does not require refrigeration before opening, although refrigeration after opening extends its life. Cartons left out for more than 2 hours should be thrown away.
See the Food Storage Guide for more information on dairy storage rules.
key takeaways
- Carton Buttermilk: Always store in the refrigerator at 40 degrees Fahrenheit or below.
- Place on interior shelf, not in door
- Left on for more than 2 hours: Discard
- Buttermilk Powder: Shelf-stable before opening, refrigerate after opening
- Freeze carton buttermilk in ice cube trays to extend life up to 3 months
Does carton buttermilk need to be refrigerated?
Yes, without any exception. Carton buttermilk is a perishable dairy product and must be kept refrigerated at all times, whether the carton is sealed or open. The USDA recommends keeping refrigerated dairy at or below 40 degrees Fahrenheit. Buttermilk left at room temperature for more than 2 hours should be discarded. On a hot day above 90 degrees Fahrenheit, that window shrinks to 1 hour.
The natural acidity of buttermilk gives it a longer shelf life than regular milk, but this acidity does not make it shelf-stable. Refrigeration is still required to keep the lactic acid bacteria that give buttermilk its tartness under control, and once the carton is opened, exposure to air and kitchen bacteria speeds spoilage regardless of pH.
Where to keep buttermilk in the fridge?
Best Storage Practices
- Internal shelf, not door: The door compartments experience temperature fluctuations every time the refrigerator is opened. An internal shelf in the middle or back maintains cold more consistently. This matters for a temperature-sensitive product like buttermilk.
- Seal tightly after each use: Exposure to air speeds up spoilage. If the carton does not seal tightly, fold it tightly or use a clip.
- Don’t put back: If you poured the buttermilk into a measuring cup, do not return any unused portion to the carton. The measuring cup may have introduced bacteria that will shorten the remaining life of the carton.
- Mark opening date: The printed date is less important than how long the carton has been open. Write the date you opened it in marker on the carton. Use within 2 weeks from that date.
- 2+ hours skipped: discard. Do not put it back in the fridge and plan to use it later. Bacteria grow rapidly at temperatures between 40 and 140 degrees Fahrenheit.
Does buttermilk powder need to be refrigerated?
Buttermilk powder is a fundamentally different product from carton buttermilk. Moisture is removed during processing, leaving dry solids behind. Without moisture, bad bacteria cannot grow. An opened canister of buttermilk powder is shelf-stable and does not require refrigeration: Keep it in a cool, dry pantry, away from heat and moisture, and it will keep for 1 to 2 years.
Once opened, the powder is exposed to air and moisture. Transferring it to an airtight container and refrigerating it extends the unopened shelf life to 6 to 12 months. In very humid climates, refrigeration is a good idea from the start, even for unopened canisters, as humidity can cause the powder to settle and deteriorate rapidly.
Can you freeze carton buttermilk?
Yes, and buttermilk is one of those dairy products that freezes best for cooking. Unlike heavy cream or half and half, which separate significantly and are primarily usable in baked applications after freezing, buttermilk handles the freezer quite well and works in baked goods with little noticeable quality difference.
The easiest way: Pour buttermilk into ice cube trays, freeze until solid, then transfer the cubes to zip-top freezer bags. Label with date. Each standard cube is about 2 tablespoons, so you can pull out exactly what’s needed for a recipe without melting a full carton. Frozen buttermilk remains safe for up to 3 months. Thaw overnight in the refrigerator, or drop frozen cubes directly into hot batter for pancakes, biscuits, or quick breads.
What happens if you leave buttermilk overnight?
Discard it. The USDA’s 2-hour rule is standard guidance for perishable dairy, and buttermilk is no exception. Even though the acidity of buttermilk provides some natural protection against bacterial growth, extended time in the temperature danger zone (between 40 and 140 degrees Fahrenheit) allows bacteria to grow to levels that can cause illness, and you can’t determine bacterial load by smell or appearance alone.
The fact that the buttermilk is already sour makes it especially easy to miscalculate here. A carton left out overnight can smell just as fresh. This does not make it safe. Toss it.
Recipes That Use Buttermilk
If your carton is nearing the end of its window, use it before turning it over. Buttermilk adds softness to this Cinnamon Pecan Crunch Banana Bread and is excellent as a marinade base for fried chicken, mixed into pancake or waffle batter, or added to biscuits and scones. It also works beyond baking: Mix it into mashed potatoes, use it in place of cream in thin soups, or stir it with olive oil and herbs for a quick salad dressing.
See also
FAQ: Can buttermilk be left out while cooking?
For short periods of time during active cooking, yes. If you’re measuring buttermilk for a recipe and it sits on the counter while you gather other ingredients, that’s okay. The USDA’s 2-hour rule takes into account the cumulative time of refrigeration. If you’re doing a longer baking session and the buttermilk will be sitting out on the counter for a long time, put the carton back in the fridge between uses.
FAQ: Is it necessary to refrigerate buttermilk after opening?
Yes. Once opened, carton buttermilk must remain refrigerated continuously. Seal the carton tightly and place on the inner shelf. Use within 2 weeks of opening. Once the seal is broken the printed date has less meaning than the date you opened. See if buttermilk goes bad to see how long it lasts and how to tell if it has gone bad.
FAQ: Is buttermilk considered a thickener? How can you tell if it’s gone bad?
Yes, buttermilk is naturally thicker than regular milk and has a mild sour smell. Some separation between liquid and solid is also normal: shake it before use and it should recombine into a pourable liquid. Signs of spoilage include a texture that is too thick to loosen even when stirred, a visible blue-green or pink mold, or an odor that is strongly musty rather than mildly pungent. See What Makes Buttermilk Go Bad for a full breakdown of normal vs. bad symptoms.
Further reading
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