Vinegar

Vinegar is a substance found in abundance across the civilized galaxy and a great deal of the uncivilized parts as well. It is, in the Guide's considered opinion, mostly harmless — though this assessment has been contested by at least one onion.

It performs three jobs at once: it preserves, it sharpens, and it gently informs every passing bacterium that the premises are closed. For the brine maker stranded far from home, vinegar is the difference between dinner and a cautionary tale.