Barm

Barm is the name given to a type of foam or froth that forms on top of fermenting liquids like beer and bread dough.

Imagine you are making a yummy cake with a special ingredient called yeast. Yeast is a tiny living thing that helps the cake rise and become fluffy. When you mix the yeast with some water and sugar, it starts to eat the sugar and produce gas bubbles. These bubbles get trapped in the dough and make it puff up.

When you leave the dough to rest and rise, the yeast starts to multiply very quickly. As they eat more and more sugar, they produce more and more gas bubbles. As the bubbles get bigger, they create this fluffy foam on top of the dough. This foam is called barm.

Barm is actually a kind of yeast itself - it's the layer of froth that sits on top of the fermenting liquid. It's made up of lots of little yeast cells that are still alive and growing. Sometimes barm is skimmed off the top of the liquid and used to start a new batch of dough or beer, because it's full of active yeast cells that can kickstart the fermentation process.

So next time you see a frothy layer on top of your beer or dough, you can impress your friends with your knowledge of barm!