What is a nonreactive saucepan?
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Clay, enamel, glass, or stainless steel. These materials don't react chemically with food. (Aluminum & copper can react, changing the taste & color).
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Ferrous metal can also alter flavors unless they have an enamel coating. Acids will react with iron pans.
some aluminum, such as calphelon, is meant to be non-reactive. It's annodized and I've used it for years with success.
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As I understand it, the *reactive* surfaces to avoid are cast-iron, copper and aluminum.
So a high-end stainless steel (such as All-Clad) or an enameled cast iron (such as Le Creuset) is the way to go when cooking with anything overly acidic like tomatoes.