Stainless steel is a non-reactive material which can go into the dishwasher, and which is lighter than traditional cast iron. “The problem with stainless steel is that it has terrible heat conductivity. It heats up slowly and unevenly compared to other materials,” says Justin Kowbel, co-founder of Borough Kitchen. “If the flame hits a certain point, you get hot patches.”
“The second type of material is copper or aluminium, which distributes heat more evenly, faster and more responsively. You can’t cook directly in it, because it’s reactive (you’ll end up oxidising everything and turning your food black), so it’s usually lined with stainless steel and/or an enamel, ceramic non-stick coating.” This, says Kowbel, is always preferable to a flimsy plastic non-stick coating such as Teflon, which will inevitably wear off (the result being that your casserole dish will need replacing).
So, enamel-coated copper or aluminium has the benefit of being easy to clean, scour-able and non-reactive, and with better heat distribution than stainless steel. Copper is also desirable looking, especially if you have it to match a set of copper pans hanging from the ceiling. However, it will tend to dull in the dishwasher.
What you really want is cast iron
What you really want, recommends Kowbel, is cast iron. “I would say that the third material, cast iron, is by far the best for locking in heat evenly – the main function of a casserole dish. The only caveat? It can be heavy, so it’s not ideal if you’ve got a bad back.”
Traditionally, a cast iron casserole dish would need to be maintained and seasoned (much like a carbon steel wok), so brands like Staub or Le Creuset also use an enamel coating inside, to save you the hassle. It can be easily rinsed with warm water (or even washed in the dishwasher – though this might cause discolouring). It distributes heat evenly and locks it in, keeping your meal warm and slowly ticking along for prolonged periods of time.
This coating of porcelain, stoneware enamel can offer either a brushed, textured or a smooth non-stick surface, made from clay that has been baked and glazed to make it very hard and durable at high temperatures. However, despite the culinary benefits of cast iron, as a material it is heavy, hard, and moderately brittle and may break if knocked or dropped.