Does Cultured Butter Need To Be Refrigerated?
You pick up your butter dish and carve out a generous dollop of soft butter, smoothly and easily gliding it over some bread. The butter is creamy and flavorful, an artisan cultured butter with just the slightest hint of tanginess — a real treat. But is it okay that you've been keeping it on the counter?
The answer is that it depends on the temperature of your kitchen and how long it's been there. According to the USDA, butter is safe at room temperature — but it can turn rancid over time. The biggest problem isn't bacterial growth, but an absorption of off smells and flavors or the butterfat itself turning bad. The more heat it's exposed to, the faster this will happen.
The founder of the cultured butter company Pepe Saya, Pierre Issa, told Delicious that in warmer climates like Australia, "you can only leave it out for around two to three days in summer and five to seven days in winter. After that, it's gone. If you can't consume a whole block of butter in that time then it needs to be kept in the fridge."
Food safety is still important to practice around the butter within that time. Cross-contamination can introduce pathogens, like putting a butter knife down on a counter that has bacteria on it and then using that knife to cut the butter. Though butter is resistant to bacterial growth, it isn't impenetrable — and pathogens multiply much more rapidly at room temperature than in the fridge.
Why can butter be left out, but other dairy can't?
You'd never leave milk on the counter for seven days. Why is it okay to leave butter on the counter that long? The answer is that the high percentage of fat — at least 80%. Bacteria needs water to grow. Butter has a high percentage of water, but it's all emulsified into the fat; each microscopic droplet of water is surrounded by fat. Bacteria struggles to penetrate fat.
Traditional, unmodified butter — cultured or not — has a "long history of safety without time/temperature control," according to the FDA. The problem with food safety at room temperature comes from agitating the emulsification through whipping or melting. When the fat begins to melt, it can separate. If the water de-emulsifies, it becomes susceptible to bacterial growth. Similarly, the FDA reports, there have been instances of whipped butter that had been "temperature abused over an extended time period" leading to outbreaks.
Cultured butter is made by introducing bacterial cultures to the cream for fermentation before churning, but they're the good kind of bacteria; they won't make you sick or contribute to your butter going bad. It's easy to determine whether or not your butter has gone bad by examining the color and the smell, but these rancidity markers won't tell you if it's contaminated with dangerous bacteria like Listeria or E. coli. If you're worried about cross-contamination, better to play it safe.
Salted versus unsalted butter
Salted butter didn't just come about because it's delicious. Before modern refrigeration, salt was an important preservative. Butter has been around since about 8,000 B.C., and along with it, foodborne illness. Refrigeration, of course, is a bit more recent. Salt has been a key tool for preserving food over the millennia because it inhibits bacterial growth. By adding salt, the butter — which is already fairly inhospitable to bacterial growth — became more shelf stable, so to speak.
The FDA states that a 3% salt concentration has been proven to inhibit all but one bacteria (Staphylococcus aureus, a pathogen that is usually harmless and found in 30% of all human noses, but sometimes causes major infections). Proper pasteurization before culturing and proper handling should prevent contamination from S. aureus — just make sure to avoid sneezing on your salted, cultured butter. Unsalted or lightly salted butter, on the other hand, is much more prone to contamination. A salt concentration of just 1% permits the growth of most foodborne pathogens. Unsalted butter is still considered to be okay at room temperature by the FDA, but it has the potential to fall victim to cross-contamination faster than salted butter.
At the end of the day, cultured butter is fine to keep at room temperature, just not for too long. The solution is to eat more butter, more often — or to put only the amount of butter you know you'll use in a few days in your butter dish.