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When Cookware Turns Food Tinny

By Cook's Illustrated Published January 2010

Recipes with acidic ingredients often call for nonreactive cookware; how much will the metals really affect the flavor of the finished products?

When acidic ingredients are cooked in “reactive” pans, such as those made of aluminum or unseasoned cast iron, trace amounts of molecules from the metal can loosen and leach into the food. Although these minute amounts are not harmful to consume, they may impart unwanted metallic flavors.

To determine for ourselves just how noticeable such flavors are, we simmered tomato sauce in an aluminum Dutch oven and in seasoned and unseasoned cast-iron Dutch ovens. As a control, we also cooked tomato sauce in a stainless-steel Dutch oven. Tasters noticed a strong taste of iron in the sauce cooked in the unseasoned cast-iron pot and a more subtle metallic taste in the sauce cooked in the aluminum pot. The sauces cooked in seasoned cast iron (which has layers of oil compounds protecting the surface of the pan) and stainless steel tasted just fine.

We then sent samples of each sauce to an independent lab to test for the presence of iron and aluminum and found that unseasoned cast iron did indeed release the most molecules of metal. The sauce from this pot contained nearly 10 times as much iron (108 mg/kg) as the sauce from the seasoned cast-iron pot, which contained only a few more milligrams of iron than the sauce from the stainless-steel pot. The sauce from the aluminum pot showed the presence of 14.3 mg/kg of aluminum, compared to less than 1 mg/kg in the sauce from the stainless-steel pot.

The verdict? Avoid reactive cookware when cooking acidic foods, since it can compromise flavor.