Preservation is a tricky business. All formulations that contain a large amount of water need to be preserved and all preservatives have some kind of drawback. Potassium sorbate has been used for a long time but has recently been very widely used in products that have some kind of natural story about them. How natural is it?
Potassium sorbate is the potassium salt of sorbic acid. Sorbic acid gets its name from the latin name for the rowan tree, and sorbic acid was first isolated from rowan berries. S0 that is a nice story. Is the potassium sorbate in the product on your bathroom shelf produced by rosy cheeked peasants harvesting rowan berries and extracting it in their cottages? Not really.
Both potassium sorbate and sorbic acid are used in vast quantities in the food industry. They are related, distantly, to sugars. In nature most sugar is burnt for energy but some gets used to make other useful bits and pieces like the sorbic acid in rowan berries. I assume in the berries it has some kind of preservative activity.
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