There's a story in Primo Levi - The periodic table where a raw onion is used in the recipe for a varnish and nobody knows why. Turns out that it was used in the

There's a story in Primo Levi - The periodic table where a raw onion is used in the recipe for a varnish and nobody knows why. Turns out that it was used in the past to measure temperature (it would fry at a certain temp) and people kept doing it even when it was no longer necessary.