Why do my potatoes go black after cooking?

Jean usually leaves potatoes to cool in the cooking water and wonders if plunging them in cold water would help. 'We’ve all been there,' sympathises spud queen Poppy O’Toole. 'It’s a harmless chemical reaction,' the author of The Potato Book continues, 'but it looks rank and only gets worse with the slow cooling process that Jean’s using.' Harold McGee, in On Food & Cooking, says the darkening is caused by the combination of iron ions, a phenolic substance (chlorogenic acid) and oxygen, which react to form a pigmented complex.

To prevent it, make the pH of the water 'distinctly acidic' by adding cream of tartar or lemon juice after the potatoes are half-cooked. Reactive metals such as a carbon steel knife or aluminium pan may also be the cause, Tom Hunt adds, so use a non-reactive metal like stainless steel.

potatoes, blackening, chlorogenic acid, iron ions, oxygen, lemon juice, acidic ph, stainless steel, aluminium pan, carbon steel