Food grade.
Potassium sorbate is synthetically produced by reacting potassium hydroxide with sorbic acid. 
It is also available naturally from some fruit berries but rarely in commercial quantity.

It is effective against yeasts and moulds but only some bacteria and works best with products that have a pH of 5.

Potassium sorbate can be used effectively with water-based products to inhibit mould.

Usually only used in products with a very high water content as in linen sprays. Cannot be used as the sole preservative in creams, etc.