The question: Can you turn cream into butter with just your arms?
Make a prediction
How many minutes do you think it will take? Write your guess on the worksheet before you start. Scientists call this a hypothesis.
What you need
1 cup heavy cream (cold)
A clean jar with a tight lid (at least 2 cups)
A pinch of salt (optional)
A strainer and a bowl
A timer
Steps
Pour the cream into the jar, add a pinch of salt and close the lid tightly.
Take turns shaking hard! Start the timer.
Notice the stages: liquid, then thick whipped cream (the sloshing stops), then suddenly a yellow lump and watery liquid.
Strain out the liquid. That is real buttermilk.
Press the butter with a spoon under cold water to rinse it, then spread it on bread.
🔬 Try shaking with a clean marble in the jar. Is it faster?
⚠️ Safety: Make sure the lid is on tight. Keep the butter in the fridge.
What's happening? The science
Cream is full of tiny drops of fat, each wrapped in a thin coating. Shaking first traps air (whipped cream). As you keep shaking, the coatings break and the fat drops bump into each other and stick together into a solid clump: butter. The thin liquid left behind is buttermilk.
Think further
Why do you think the cream must be cold?
Where else in cooking do we whip air into something?
