Several of our consulted chefs agreed that cast iron can leave an unpleasant flavor layer in tomato-based dishes. The "naked" cast-iron cooking surface of an unenameled skillet can cause "acidic foods to become discolored and acquire a metallic taste," says Weinstein.
So can you use cast iron when making tomato-based foods? Sadly, the answer is it is best not to. Acidic foods that require a long simmer can ruin all that seasoning you worked so hard to achieve. In turn, it will make your food taste a little tinny.
Roast your tomatoes in a cast-iron pan instead of a baking sheet, at 400°F instead of 350°F (or on a grill rather than in the oven), and replace the quartered shallots with shaved ones.
Do not use an aluminum pot, pan or utensil when cooking tomatoes. The acid in the tomato reacts unfavorably with the aluminum. Using aluminum makes the cooked tomatoes more bitter and fades the color. The dish will also absorb some of the aluminum and the acid in the tomatoes can pit and discolor the aluminum cookware.
After cooking, allow the cookware to cool, then use a pan scraper to remove stuck-on food, scrub with a nylon brush or nonscratch pad, hand dry, and add a generous layer of oil. Rub the oil onto the pan until it is evenly distributed.
I still own enamel-covered cast iron pots and pans that I purchased years ago (I like the colors that they add to our kitchen). But I use them sparingly, thoughtfully, and won't replace them when they are finally discarded. They might be one of the safest pans to cook with when cooking tomatoes and other acidic foods.
Cast-Iron Skillet
Not only are they our go-to for searing steaks or cooking frittatas, but this oven-proof skillet is fantastic for roasting. It has the same thick walls and low sides as a roasting pan (and at a fraction of the cost).
One of our staff members advised: "The acidity in tomatoes can react with the metal, potentially giving the food a metallic taste and damaging the pan's seasoning." However, based on my experience using a nitrided carbon steel frypan from our own brand, I've had no issues cooking tomatoes.
You let your skillet soak.
Soaking your cast iron skillet in your sink is a recipe for rust, as is washing it in the dishwasher. Instead, clean it ASAP, even using simple soap and water if you must.
Eggs fall into the category of sticky foods that are not ideal for cast iron skillets that haven't built up their seasoning yet. While cast iron can become non-stick with sufficient use over time, a newer skillet will almost certainly cause your eggs to stick to its porous surface.
Acidic foods (unless you make it snappy)
Acidic foods (like tomato sauce, wine-braised meats, etc.) enter the red zone when they spend too much time cooking in the skillet.
Cast iron cookware's disadvantages include its heavy weight, the need for seasoning and maintenance, potential reaction with acidic foods, and lack of slickness for delicate cooking tasks.
But in the case of tomatoes, the delicate, acidic fruit can adversely react with the metal, altering the taste of the food and potentially damaging the cookware. There are also potential health concerns specifically with mixing aluminum and acidic foods, making tomatoes a definite food to keep away from the metal.
Common cooking oils like olive oil will gradually produce seasoning, but won't be as effective as grapeseed oil. Canola, other vegetable oils, and shortening are a little better.
Never cook acidic foods in a cast iron skillet.
You can sauté cherry tomatoes in cast iron, but don't try making a long-simmering tomato sauce. If you recently purchased your skillet and it still needs to be "broken in," acidic ingredients can erode the seasoning and even make foods taste metallic.
You should season a cast-iron skillet at least once a month, but seasoning it after each time you cook with it also works. You may not need to repeat the entire seasoning process as you did before initially using it, but after each use, rinse it and give your cast-iron skillet a quick season by oiling it.
First, the black specks you see coming off into your food are not harmful. They are most likely carbon deposits. This happens due to overheating of fats and oils. Using an oil with a low smoke point will carbonize at high temperatures and cause residue from the pores of your pan to rub off onto your food.
Even when you're roasting vegetables, an aluminum baking sheet will give you a faster cooking time, offer more space than a standard roasting pan, trap less steam, and be easier to handle.
Your food will stick and burn. You will have to scrub, scrape, etc. until the food debris is removed. Seasoning a cast iron pan is very simple and should take about 30 mins or so.
Never use an aluminum pot, pan or utensil when cooking tomatoes, or any other soft metal items for that matter. The acidity in the tomato doesn't do well with them, they create a chemical reaction and can turn cooked tomatoes bitter, fades the color and the food will absorb some of the aluminum!
For our recommendations, we stick to stainless steel, cast iron, and enamel or ceramic coatings. If you're making the switch from traditional nonstick cookware, you should look into ceramic or enameled cookware.