Metal leaching occurs when the food you’re cooking chemically interacts with the pot or pan you’re cooking with, especially with acidic foods over long periods of time. This can happen in aluminum, cast iron, or stainless steel cookware in different ways. While metal leaching can potentially alter the food you’re cooking and the cookware you’re using, there are no significant health concerns related to metal leaching.
Uncoated aluminum cookware is quite rare these days, but you will still sometimes see uncoated aluminum bakeware. Aluminum as a metal is quite reactive and so metal leaching will occur.
What metal it leaches: Aluminum
How it affects health: According to tests done by Cook’s Illustrated, the added aluminum in your food is extremely negligible, even when cooking acidic foods like tomato sauce and lemon curd. This is backed up by another study that finds that incremental intake of aluminum from cooking vessels constitutes less than 5% of normal daily intake.
How it affects flavor: Cook’s Illustrated found that leaching this can affect the taste of your food, and introduce “an unpleasant metallic taste”.
How it affects cookware: Over time the cookware will become corroded and degraded.
Cast Iron Cookware
Cast iron cookware is tremendously popular, but has some drawbacks including metal leaching.
What metal it leaches: Iron
How it affects health: Iron is an essential nutrient that has important uses and is present naturally in a variety of foods. Cooking in cast iron can significantly increase iron intake, but not to a level that would be at all dangerous. The one exception may be for people with hemochromatosis.
How it affects flavor: Similar to aluminum cookware, cast iron can introduce “unwanted metallic flavors,” according to America’s Test Kitchen.
How it affects cookware: Metal leaching in cast iron due to cooking with acidic ingredients will strip away the pan’s seasoning, making the pan susceptible to rusting.
Stainless Steel Cookware
Unlike aluminum and cast iron cookware, stainless steel is an alloy made from a combination of metals, making it more durable.
What metals it leaches: Chromium and nickel
How it affects health: Some people experience nickel and chromium sensitivities or allergies, with symptoms resulting from direct skin contact with the metals. This has caused concern that those sensitive people may also experience symptoms when eating foods cooked in stainless steel cookware. However, according to a recent study on cooking with stainless steel, "the amounts released were below known allergy-triggering thresholds”. Further, the low levels of metal leaching are further reduced the more the cookware is used. For those with nickel and chromium allergies, it is much more important to choose a diet with foods low in nickel and chromium, as that is where the majority of daily intake comes from.
How it affects flavor: It doesn’t! The quantities of leached metal are so miniscule that they won’t have any effect on the food’s flavor.
How it affects cookware: For the most part, metal leaching and general corrosion from exposure to acidic ingredients will not significantly affect stainless steel cookware. Salt pitting, however, is a different story, and is why we choose to use 316Ti to strengthen the cooking surface of our cookware.
The Bottom Line
Metal leaching does occur to varying degrees with uncoated metal based types of cookware. For aluminum and cast iron cookware, that means some recipes should be off-limits because they’ll end up tasting gross and will harm your cookware. For stainless steel, feel free to cook whatever you’d like! And for all of these types of cookware, metal leaching poses no significant health risks.