Cooking tomatoes or other overly acidic food in your cast-iron skillet can cause some of the iron to leach out, causing your food to taste metallic.
Before you rule out tomatoes altogether, once your skillet is well seasoned, it should be able to withstand acidic food.
According to The Kitchn, "If the seasoning is very good, you can prepare dishes with tomatoes and other acidic foods, but it’s best to wait until your piece is well-seasoned."
How to season your cast-iron skillet
Seasoning relies on baking cooking oil or vegetable shortening into cast-iron skillets and pans at high temperatures. It seals interior and exterior surfaces to keep out moisture, prevent rust from forming, and create a smooth, shiny surface that quickly releases cooking foods. Proper cleaning -- rinsing with hot water (soap and abrasives are no-nos), wiping away grime, rinsing, drying, and applying oil -- maintains the cast iron's original seasoned finish and, along with regular use, continually enhances the skillet's nonstick properties.
Cast-iron skillets are sold as unseasoned and factory-seasoned versions, so read product labels before you buy. Those with preseasoned finishes are ready for service and can be used right away to bake a frittata, saute vegetables, or fry chicken.
You will need to season cast-iron skillets sold without a factory-seasoned finish by following the steps below.
Note that the experts at Lodge Manufacturing, makers of preseasoned cast-iron skillets, say these seasoning steps can be used to refurbish cast-iron skillets and pans that have lost their nonstick attributes and have dull, greying or rust finishes.
How to Season Cast Iron in 7 Simple Steps
- Protect the oven's bottom rack from dripping oil with a sheet of aluminium foil. Preheat the oven to between 350 and 400 degrees Fahrenheit.
- Wash your cast-iron skillet (or another type of cast-iron pan) with a stiff brush or a scrub pad and hot, soapy water. When preparing a cast-iron skillet for seasoning or re-seasoning, it's OK to use soap and plenty of elbow grease because you have not yet applied the final coating of cooking oil.
- Rinse the cast-iron skillet with hot water and dry thoroughly; make sure all soap residue and moisture have been removed.
- Use a paper towel or clean rag to evenly apply a very thin coating of cooking oil (any cooking oil will do) or melted vegetable shortening to the cast-iron skillet's surfaces.
- Set the cast-iron skillet upside down on the oven's top rack -- turning the pan bottom-up prevents excess oil from puddling on the skillet's cooking surface.
- Bake the cast-iron skillet or another cast-iron pan for an hour; turn off the heat and leave to cool inside the oven.
- Store the cool, now-seasoned cast-iron skillet in a dry area away from cooktops, sinks, and dishwashers. Use it often and clean it properly, and your perfectly seasoned cast-iron skillet will last at least a lifetime or more.