Bone broths are one of the biggest food trends of the past few years, but making your own stock is nothing new. Cooks who have made their own chicken stock before have likely noticed a layer of foam forming on top of the simmering broth, and while this sight can be worrying if you don't know what causes it, it's completely harmless.

This foam is called soup scum, and according to Bon Appétit, it forms on top of meat broths because of "rogue proteins that coagulate when heated." These proteins are leached out of meat, bones, and vegetables by heat, and once they're out in the open, they become viscous and form bubbles, creating foam.

While soup scum is not harmful to ingest, most cooks remove it so the broth doesn't turn an unappealing grayish color. The best time to do so is when the broth reaches the boiling point; just use a slotted spoon or fine mesh strainer to skim suds off the surface of the broth, until the liquid is clear and no more foam is forming.