How Is Soap Made?

Step 1 of 5

Water alone cannot shift grease.

Water molecules cling to each other and to other watery things. Grease is not watery, so water runs straight past it — you can rinse a greasy plate all day and it stays greasy.

Step 2 of 5

Soap has one end of each kind.

A soap molecule is a long tail that likes grease with a head on the end that likes water. That is the entire invention — one molecule that can hold onto both things at once.

Step 3 of 5

It surrounds the grease and lifts it.

The tails bury themselves in a spot of grease while all the heads point outward into the water. The grease ends up in a little ball wrapped in soap, and the water can now carry it away.

Step 4 of 5

Making it changes the fat completely.

Cook fat with a strong alkali and the fat molecules are cut apart and rebuilt with a water-loving end. Neither ingredient cleans anything; the thing you make out of them does.

Step 5 of 5

It is how you stop a virus, too.

Many viruses are wrapped in a greasy coat. Soap tears that coat apart in exactly the same way it lifts grease off a plate — which is why washing hands works so well and so cheaply.

Hard water contains dissolved minerals that grab soap and make grey scum. Detergents were invented partly to get around exactly that.