Why do I hate soggy crisps but love crunchy ones?

Think of opening a brand new bag of crisps. You pop one in your mouth and bite down. Crunch! Listen to that loud, happy crack between your teeth.

Now picture a crisp from a bag that stayed open all day. It feels soft and bendy, and it tastes all wrong. So why do you hate soggy crisps but love crunchy ones?

A fresh crisp is a thin slice of potato with almost no water left inside. Being this dry makes it brittle, which means it breaks with a sharp snap instead of bending. A dry twig on the path does the same thing when you step on it.

When you bite, your teeth press on the crisp until it snaps. Cracks race through it in lots of quick little jumps, and each crack makes a sound. Together, those sounds make the crunch you hear right inside your head.

Your brain listens to that crunch. Fresh apples and fresh carrots crunch too, and old ones go soft, so your brain has learned that crunch means fresh. That is why a brittle crisp feels like a real treat.

The air all around you holds moisture, which means tiny bits of water too small to see. You cannot feel it, yet it drifts right into an open crisp bag. What do you think happens when that moisture meets a dry crisp?

Because the crisp is so dry, it soaks up the moisture bit by bit, the way a dry sponge drinks up water. Hour after hour, the crisp grows damp inside.

A damp crisp is not brittle anymore. When you bite it, it bends and squashes instead of snapping. With no sharp cracks, there is no crunch, only a soft, quiet squish.

Your brain hears that quiet squish and feels the bendy bite. It decides this crisp is old, not fresh, just like a soft, wrinkly apple. That is why a soggy crisp tastes so wrong to you.

Brittle, moisture. You love crunchy crisps because a dry, brittle crisp snaps with a loud crunch that tells your brain it is fresh, and you hate soggy ones because moisture from the air makes them bend quietly, so your brain decides they are old.

Next time you hear a happy crunch, you will know your clever brain is listening, so sweet dreams and sleep tight.