Cast iron cookware must be among the most versatile and beloved of all kitchen implements. It's equally useful on the stove top and in the oven, capable of pitching in on the grill or even a campfire. It sears, it sautes, it deep-fries and it bakes. The list of cooking tasks for which cast iron cookware is the best choice is a long one, yet there are a few foods that stand out as exceptions. Avoid highly acidic ingredients to prevent damaging your pans and diminishing the deliciousness of your meal. You should also assess the slickness of the pan's seasoning before tackling typically stickable fare.
To comprehend why certain foods are unsuitable for cast iron pans, you need to understand the seasoning process. Seasoning is the build-up of baked-on layers of polymerized fat, which seals the tiny pores in cast iron. Seasoning creates a hardy, slick surface for non-stick cooking and a barrier between food and metal. Most modern cast iron pans come pre-seasoned. With regular use and proper handling, as well as occasional re-seasoning, the non-stick properties of cast iron cookware improve considerably over time.
Avoid Acidic Ingredients
As a general rule, avoid cooking highly acidic foods in cast iron pans. Common examples include tomatoes, wine, vinegar, apples and citrus fruits or juices. Unless the pan is perfectly seasoned, the acids in these foods can react with any exposed metal, causing minute amounts of iron to transfer from the pan to the food. This can cause a noticeable metallic taste as well as discoloration. Acidic foods can also damage the pan's seasoning and dull its finish. The longer the acidic food is cooked, the greater the risk of these undesirable results. A pan that is not well-seasoned is also more susceptible.
Breaking the Rules
Acidic foods in some circumstances will fare just fine in cast iron cookware. Consider the degree of contact between the acidic food and the surface of the pan. For example, tomatoes are acidic, but breaded and fried green tomatoes are not problematic because breading and oil come between the acidic food and the metal. Adding vinegary marinated olives or jalapenos to cornbread batter and baking the mixture in a cast iron skillet should likewise be successful, because there is very little, if any, direct contact between metal and acidic food. Deep-fried apple fritters are also viable for the same reason.
Another reason to "break the rules" is because you have full confidence in the seasoning of your pan. Anecdotal evidence suggests that a very well-seasoned cast iron pan can handle acidic foods with shorter cooking times without detriment to either the pan or the food. So, adding a splash of wine to a quick pan sauce is a risk you might be willing to take, but slowly simmering a tomato-rich bolognese is probably best avoided.
A Sticky Situation
Only very well-seasoned cast iron pans can handle foods that tend to stick, such as fried eggs, crepes, omelets and delicate fish. A newer cast iron pan, one with questionable seasoning or one with any traces of burnt-on food residue, is not a good choice for cooking such items. Teflon-coated non-stick cookware is likely better for the task.
Because it is somewhat porous, cast iron has a tendency to absorb and retain stronger flavors and aromas. Washing diminishes this effect, but it can still be noticeable if you cook something mild tasting, such as a creamy sauce, immediately after cooking something relatively strong, such as fish or a spicy curry. Use a different pan or let the cast iron cookware go through a series of uses and washes to avoid the unwanted transfer of flavors and aromas. If you regularly use cast iron pans for both savory and sweet dishes, Bon Appetit magazine recommends designating a separate pan for each use.