Ask A Scientist: Fatty, Fatty Two By Four
Question: “Why can you whip cream but not milk?” -Michael W Syracuse, NY
Answer: Oh, whipped cream. So decadent and fluffy, a favorite all around. Pies just wouldn’t be the same without that rich vanilla scented goodness. Sundaes would just be ice cream in a bowl with crap all over it without this magical dessert topping. Unfortunately there is absolutely no cheating with your dairy products on this one- its cream or nothing for this heavenly foam. I’ll explain why, as it really boils down to how a stable foam is created.
Whipped cream is nothing more than a foam made from air and water that is stabilized by milk fat. Sounds similar to that creamy rich foam on top of your cappuccino, right? Basically, it is. However, milk foam has a tendency to collapse upon itself quickly due to the low viscosity of the liquid and the way that the fat interacts with the water when a bubble wall is created. The milk proteins don’t unfold at all and milk has a tenth of the fat of heavy cream’s 36% minimum. The fat, rather than the protein is what bonds with the other components in the dairy products to form a stable structure.
When making whipped cream, the cream is aerated through whipping it rapidly with a whisk. As air is folded in to the dense cream, tiny bubbles form from the water in the product. This forms your basic foam, which is unstable. Cream creates the ideal stable dairy foam because the more concentrated fat molecules bond with the water in the cream like a net to form a stable trap for air.
Another reason why milk doesn’t work well for creating stable foams is because generally speaking, the milk is homogenized while cream is not. (Both are pasteurized.) homogenization stabilizes the milk fat in dairy products by breaking down the moderately large fat molecules into smaller molecules, which allows the milk proteins to bond to readily to prevent separation. By breaking down the fat through homogenization the milk will not separate but it also won’t help for dessert toppings. Those smaller fat molecules don’t lend themselves to creating a stable foam as it would be similar to trying to patch a hole in a wall with paper mache strips.
Although there are many hints and tricks to perfecting whipped cream that I won’t cover here, the quick answer to why cream whips better than milk does comes down to the fat content, viscosity and how foams are created. A fun topic to impress your friends over dessert with, I’m sure!
-By Hannah Nordgren, Science Enthusiast