If matter expands when heated, why does most food shrink when being cooked?
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Most food has water in it, and some of that water is boiled away when you heat it- that’s most of the shrinkage. That’s why a hamburger patty or a roasted vegetable is going to shrink when you cook it.
Then think about pasta or rice. Those increase in size when you cook them- because they start dry and then absorb more water.
Most food contains water and the water evaporates as you heat your food up. Additionally grease may melt inside the food and flow out causing your food to shrink.
Boiling something dried will make it expand, think of pasta and rice.
When you’re cooking, you’re typically above the boiling point of water, which causes it to evaporate from the food and shrinks it. Juices coming from the food also reduce its apparent mass. Lastly, some solids (like fat) will liquify and flow out from the food.
Food does expand when it’s hot and retracts when it is cool. What you are seeing is because food looses mass when it is being cooked – mostly through steam or fat rendering out but there are some other reactions that can happen to make the food loose mass.
>If matter expands when heated, why does most food shrink when being cooked?
For the same reason you won’t end up with a bigger house when you burn it down.
Your food (and most any thing around you) isn’t just “matter”, it’s a complex structure, a type of building. Multiple different buildings with unique structures and characteristics, in fact!
Denature the proteins, boil off the water, break down the cell walls… there are many ways to destroy those buildings via heat – you’re not merely making them *warm*.
In addition to the other comments noting that water and fat are lost, I just want to add that if it’s a protein being cooked, then one thing that also happens is that the proteins, which you might think of as stretched-out rubber bands for this purpose, scrunch back on themselves.
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