That everyday mystery that no one has ever really explained to you (and that messes up your kitchen every time)
We’ve all been there: you put a pot of milk on the stove, look away for two seconds… and boom. Milk everywhere. Hissing, bubbling, overflowing, burning onto the stovetop. Sticky mess, burnt smell: total chaos.
But why is milk so unpredictable?
Spoiler: it’s all science.
Milk: calm on the outside, chaos on the inside
As food scientist Christophe Lavelle explains, milk isn’t just “white water.” It’s made of about 10% proteins, fats, and sugars and these are exactly what make it so temperamental when heated.
Just like water, milk forms steam bubbles as it heats.
But here’s the twist: the proteins in milk cling to the bubbles and stabilize them.
Instead of popping, the bubbles pile up and form a thick foam.
And that’s not all.
As milk heats, a thin skin forms on the surface: a layer of coagulated proteins and fat. This skin acts like a lid, trapping the growing foam underneath… until the pressure becomes too much.
Then?
Milky volcano.
It’s not just milk: pasta water does it too
Yes, that pasta water eruption is caused by the same scientific principle. Except this time, the culprit isn’t protein: it’s starch. Starch thickens the water and traps the bubbles, forming foam that climbs up and spills over.
Result: a hot, starchy geyser all over your stovetop.
How to stop the boiling-over drama?
The good news? Science also gives us solutions:
1. Turn down the heat
High heat ramps up bubbling too quickly. Low, gradual heating gives bubbles time to rise and burst instead of overflowing.
2. Use a larger pot
Obvious but effective: more room = fewer eruptions.
3. The wooden spoon trick
Placing a wooden spoon across the top can break some bubbles and delay overflow. It’s not magic, though: don’t leave the kitchen trusting it 100%.
4. Use a “milk watcher” disc
These small ceramic or metal discs sit on the bottom of your pot. They help steam form into larger bubbles that burst more easily and they make a clicking sound when milk is close to boiling.
A built-in alarm for distracted cooks.
In a nutshell
- Milk overflows because it foams and a layer of protein and fat prevents the bubbles from escaping.
- The key is to heat gently, leave room in the pan and, ideally, stay close by (sorry, no miracles here).
And the next time someone tells you to "keep an eye on it", you'll know it's not just an expression: it's a true principle of culinary physics ;)
Adèle Peyches
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