Attempting to spread cold butter is one of life’s small tragedies.
It’s exacerbated by the waiting presence of a wonderfully fresh baguette, or a just-toasted English muffin replete with crags and stalagmites. Scrape, scrape, scrape. Sigh.
The appeal of room-temperature butter is obvious in these instances, but the question remains: Is it ever safe to leave a stick unrefrigerated? We asked the butter experts.
The sum of their answers: Yes, it’s fine to leave butter unrefrigerated for small periods of time, but ideally not longer than a day or two. Refrigeration preserves butter’s best flavor and extends its shelf life, but room-temperature butter probably isn’t too big of a health risk.
Refrigerator temperatures reduce the growth rates of spoilage microbes on butter, says Peter Cassell, press officer for the U.S. Food and Drug Administration. Lower temperatures and less exposure to light also reduce rates of oxidative rancidity, the process by which oxygen in the air can create a rancid smell and taste in oils and fats. For these reasons, the FDA’s Foodsaver guidelines recommend butter be stored at room temperature for only a day or two, while it can be refrigerated for up to two months. California Dairy also advises limiting butter’s storage at room temperature to “short periods of time.”
“The longer you leave it out at warmer temperatures, the more issues you’ll have with food safety—although there aren’t many food safety concerns—but more so quality concerns,” says Chris Galen, spokesperson for the National Milk Producers Federation. “At around 68 degrees, butter can start to oil off, meaning the oil de-emulsifies from the solid. It’s not a safety issue but a quality issue for people who care about either the mouthfeel or look of it.”
The Wisconsin Milk Marketing Board agrees that concerns about bacteria or food safety aren’t the primary reason you should refrigerate butter.
“The general composition of butter, an emulsion with both a high fat and high salt content, makes it a fairly inhospitable environment for bacterial growth,” according to Adam Brock, Director of Technical Services at WMMB. “Leaving butter out for a few hours, or a few days, will not result in bacterial growth that would create a food safety issue.”
He adds that pasteurized, salted butter will last longer than pasteurized, unsalted butter, and that placing butter in a dish at room temperature will slow the oxidation process.
Bottom line: Leaving a stick of butter at room temperature for a few days won’t harm you, but it could cause your butter to spoil faster and potentially absorb unwanted smells from the rest of your kitchen. Best butter practices say to leave just the amount you want to spread at room temperature and to use it up promptly.
All this being said, try not to pass judgment too harshly on those who insist upon treating their butter differently from you, since butter rules are—like butter itself—kinda squishy.
“There’s not a hard and fast correct answer on this, as with so many other things in life,” National Milk Producers Federation’s Chris Galen says. “There’s some gray area here.”