You’ve probably heard it’s not a good idea to cook acidic foods like tomato sauces, wine sauces, or chilis in cast iron because the iron could leach into the food and add a bitter, metallic taste. Well, America’s Test Kitchen put that theory (and some others) to the test, and the bottom line? It’s fine.
First of all, it’s absolutely true that when you cook acidic ingredients in cast iron for extended periods of time, trace amounts of iron molecules from the metal can get into your food. The good news though is that first, it’s not bad for you at all, and second, you won’t taste it. In fact, America’s Test Kitchen says that it won’t even be noticeable unless you’re cooking for a long time. To test the theory, they simmered a highly acidic tomato sauce over medium heat in a cast iron skillet and checked every 15 minutes for off flavors and any damage the sauce may have caused to the pan:
1The Myth: You can’t cook wine, tomatoes, or other acidic ingredients in a cast-iron pan.
THE TESTING: When acidic ingredients are cooked in cast iron for an extended amount of time, 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, and the pan’s seasoning can be damaged as well. To test how fast this happens and how noticeable it is, we made a highly acidic tomato sauce and simmered it in a well-seasoned skillet, testing it every 15 minutes to check for off-flavors and damage to the pan.
THE TAKEAWAY: In the end, our tasters could detect metallic flavors in the tomato sauce only after it had simmered for a full 30 minutes. So, while you can definitely cook with acidic ingredients in your cast-iron skillet, you have to be careful. First, make sure your pan is well seasoned; seasoning keeps the acid from interacting with the iron—to a point. An acidic sauce can afford a brief stay in a well-seasoned pan with no dire consequences. You should also be careful to remove acidic dishes from the skillet after they finish cooking; don’t let them sit too long in the warm skillet and transfer any leftovers to an airtight container. (These rules do not apply to enameled cast-iron skillets; the enameled coating makes it safe to cook acidic ingredients for any length of time.)
All of our cast-iron recipes have been carefully developed to work in cast iron, even when they use highly acidic ingredients like vinegar, wine, tomatoes, cherries, and stone fruits. We use tricks like shorter simmering times, diluting the problematic ingredients to make the pH less of an issue, and waiting until late in the recipe to add the acidic ingredients. If you do accidentally oversimmer an acidic ingredient, you may have to throw out the food, but you can simply reseason your skillet and get back to cooking in it again.
2The Myth: One of cast iron’s greatest advantages is that it heats really evenly.
THE TESTING: We were interested in this question because it would affect the way we went about preheating our skillets for cooking. To see just how the pans reacted when placed over heat, we designed a test that would give us a visual indication of the way heat traveled through the cast iron. We spread 1 tablespoon of all-purpose flour in both our favorite cast-iron skillet and a traditional stainless-steel skillet and heated them over medium heat until the flour started to toast. As the flour browned in the hot pans, it essentially created a map of how each skillet heated up.
THE TAKEAWAY: While the flour in the stainless-steel skillet toasted evenly to a uniform golden brown (below, left), the flour in our cast-iron skillet started to burn in some spots before other areas of the skillet had any browning at all (below, right). It turns out that because cast iron is such a poor conductor, it in fact heats very unevenly on the stove—and more or less so depending on the level of heat you use. To work around this, we preheat the skillet in a 500-degree oven when we need a really good, even, fast sear. The better heat distribution in the oven helps the pan heat more evenly, creating a superior surface for searing. For recipes where a strong sear isn’t necessary, we preheat the pan for either 3 or 5 minutes over medium-high heat on the stovetop, which we found to be the best way to get relatively even heat without too much work.
3The Myth: Cast-iron skillets work only on gas stoves; you can’t cook with them on an electric range.
THE TESTING: Part of our testing procedure for the recipes in this book was to make them not only in both traditional and enameled cast-iron skillets but also on both gas and electric stoves. We know that almost half of our readers are likely to use electric stoves in their home kitchens, so we wanted to make sure our recipes would work for them, especially since some people think that cast iron and electric stoves don’t mix well.
THE TAKEAWAY: We mostly found that cast iron works great on electric, although it may take a little longer to achieve the same results since cast iron is slightly slower to heat on an electric heating element. If you’re using a cast-iron skillet on an electric range, you may find that you need to cook things slightly longer—use the upper ends of the timing ranges given in our recipes. If you have a glass-top range, you should also take extra care when moving the heavy cast-iron pan around on the stove to avoid any scratching or damage.
4The Myth: You should never wash cast iron with soap.
THE TESTING: During our extensive recipe-testing process we generated hundreds of dirty skillets and thus had plenty of opportunities to test different cleaning methods. While developing our recommended procedure, we experimented with a variety of cleansers, including dish soap and scouring powders.
THE TAKEAWAY: We found that a few drops of dish soap are not enough to interfere with the polymerized bonds on the surface of a well-seasoned cast-iron skillet. Don’t scrub the pan with abrasives like steel wool or use harsh cleansers like Comet, and don’t soak the pan, since those things can definitely affect the seasoning, but it’s OK to use a few drops of dish soap if you need to clean up a particularly greasy pan, or even if that just makes you feel more comfortable with your cast iron. Just make sure you rinse the pan clean and wipe it dry when you’re finished.
5The Myth: If a cast-iron pan gets rusted, it’s ruined.
THE TESTING: Because cast iron is so durable, old cast-iron pans are a common find at thrift stores, antique shops, and flea markets. But older cast iron may not always be in tip-top shape. To find out whether even the most damaged cast iron could still be salvaged, we took the most abused skillets we could find; completely stripped them of all their dirt, rust, and ruined seasoning by sending them through the self-cleaning cycle on our oven; and then tried reseasoning them from scratch.
THE TAKEAWAY: It takes a lot to kill a cast-iron skillet. If yours has a crack in it from improper use or storage, or if it has literally rusted through, it’s time to throw it out, but unless the structure of the pan has been truly compromised, there isn’t much that can “ruin” a cast-iron skillet. Even if the seasoning gets seriously marred or the pan starts to rust, you can clean it off and start fresh.
6The Myth: When you cook in a cast-iron skillet, your food will absorb a lot of extra iron so you can effectively supplement your diet by using this type of pan.
THE TESTING: We simmered tomato sauce in a stainless-steel pan and in seasoned and unseasoned cast-iron pans. We then sent samples of each sauce to an independent lab to test for the presence of iron. The unseasoned cast iron released 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 than the sauce from the stainless-steel pot.
THE TAKEAWAY: Since this occurs in pronounced amounts only with unseasoned skillets, which you wouldn’t use for cooking, we don’t consider this an issue. A seasoned cast-iron skillet will not leach any appreciable amount of iron into food cooked in it.