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Why does lipstick destroy foam?

It’s not just the fats in lipstick that destroy foam - the fats in crisps, nuts and pork scratchings, as well as the natural oils in moustaches all diminish the head of a beer.

The head is created by bubbles of gas, often carbon dioxide or nitrogen, that are released as your pint is being pulled. These bubbles are coated with a strong skin of proteins that originate from the malted barley used during the brewing process and which helps the bubbles to form a stable foam. But when fats or detergents come into contact with the foam, they can literally punch holes in the protein skin, weakening and destabilising the bubbles and destroying the head.

A technique known as Atomic Force Microscopy, which can study the surface of bubbles at very small scales, has shown these holes in the surface of the protein skin.

Scientists at the Institute of Food Research in Norwich have been investigating how beer foam can be made to resist the ravages of oils and fats. They’ve found that the protein skin can be made stronger by adding compounds called hop acids which help to bind the beer proteins together. Another additive is a seaweed extract which thickens and strengthens the protein skin. And looking to the future, the researchers have recently patented a method of extracting a natural molecule from excess grain that is normally thrown away in the hope of using it to make more stable beer foams.

But preserving your head doesn’t have to involve strengthening the bubbles. Another method is to keep the fats away from the foam in the first place. Barley proteins are thought to have small pockets in which fat molecules can sit. So by ensuring that barley proteins aren’t lost in the brewing process, brewers can ensure that there are fewer fat molecules available to go on a bubble bursting rampage.

(via: Physics.org )