What is potato whitener?

"Potato whitener" is not a commonly used term in the culinary world. It's possible you're thinking of something else, perhaps:

* Potato starch: This is a fine white powder made from potatoes, often used as a thickening agent in sauces, soups, and gravies.

* Bleaching agents for potatoes: While not typically used in home kitchens, some industrial processes use bleaching agents to whiten potatoes before they are processed into products like potato chips or French fries. These agents are typically approved for food use and are safe for consumption in small amounts.

* A slang term: It's possible "potato whitener" is a colloquialism used in a specific region or community. Without further context, it's difficult to determine the intended meaning.

If you can provide more information about the context in which you encountered this term, I might be able to give you a more specific answer.