Most people take a few basics along when they travel, like underwear, a toothbrush, and a change of clothes. Apparently Kate Beckinsale adds butter to her list.
The actress tells People in a new interview that she tends to pack her own butter (specifically Kerrygold grass-fed butter) when she travels. "I find it quite hard to get ahold of," Beckinsale says. "If I'm going from one city to another, I'll put some in my suitcase to make sure I have it. I'm the crazy person traveling with butter."
This raises a major question: Is that safe?
It's a little tricky, Darin Detwiler, PhD, director of the Regulatory Affairs of Food and Food Industries program at Northeastern University, tells Yahoo Lifestyle. "Butter is interesting because there is dairy in it, but it's mostly fat," he says. "And fat doesn't exactly help bacterial growth."
But there are a few things that can happen if you don't refrigerate your butter, especially if you keep it out for a long period of time or don't refrigerate it at all, Detwiler says. One is that it can go rancid. "You'll know right away," he says. Another is that you can get foodborne bacteria like E. coli or salmonella, which can grow on the butter and infect you. Finally, if you leave your butter out, there's more of a chance for cross contamination with other foods and bacteria that may be in your kitchen. "The more you leave it out, the more you're leaving it open to cross-contamination or the bacterial growth," Detwiler says. "You really have to take that into consideration."
Still, plenty of people don't refrigerate their butter or at least leave it sitting out for longer periods of time and do just fine. "It's about the level of risk you're willing to take," Detwiler says. "Just because butter is less likely than other foods to give you a foodborne illness doesn't mean there's zero chance."
Whether the butter is salted or not makes a big difference, Benjamin Chapman, PhD, an assistant professor and food safety extension specialist at North Carolina State University, tells Yahoo Lifestyle. "Most salted butter [creates a] 10 to 15 percent salt water concentration for the micro droplets of water in the butter," he explains. "That's important because foodborne pathogens need water to grow. But they don't like salt water at 10 to 15 percent very much."
If butter is unsalted, "pathogens could be introduced into the water droplets when someone sticks a knife into the stick, and they could grow," Chapman says. "Salted, it's unlikely."
If you like to keep your butter out or, like Beckinsale, you like to travel with it, there are a few things you can do to lower your risk of it going bad. "Keep it in an airtight container, keep it out of the sun, and try to keep it as cool as possible," Detwiler advises. "That's better than nothing."
Of course it's possible to leave your butter out and be just fine, but it's important to know that it's not risk-free. "You can argue this all you want, but here's the real argument: Why take a risk?" Detwiler says.