I knew that question was coming, reader Wolfe, thanks for pulling the trigger. It’s a good time to discuss this since we’re on the subject of butterfat globules and such. As you remember from the post below, the protein membranes that surround fat globules tend to break when you apply shear forces to them. That allows the butterfat molecules they contain to escape, which can be a good thing up to a point.
If there happens to be an air bubble nearby, those free fats will flock to its surface. Why? Because cream is watery and fats hate water. Bubbles are of course another effect of agitating cream, so the two effects of whipping — more free fat and more bubbles — reinforce each other (literally). If the cream is chilly, the free fats will start forming crystals which create walls around the air bubbles, keeping them from popping. The cream gains volume.
This is all well and good so long as the whipping doesn’t go on for too long. If it does the fat crystals get too massive and rip away from the bubble surfaces. The bubbles pop and the cream loses volume as butter grains begin to form. Then it’s pretty much all over for the dessert topping…but just the beginning of the toast spread!
It’s important to remember that it’s not just any cream that can whip. Cream must have a fat content of at least 30%. That’s a virtual impossibility for naturally separated cream, which is why you didn’t see a whole lot of whipped cream before the cream separator was invented about 100 years ago. Prior to that time whipping cream was incredibly laborious. It took well over an hour to produce as cooks skimmed spoonfuls of froth off quantities of manually separated cream that they’d beat and beat and beat and…
Mother technology, where would we be without you?