A nonreactive pan is one that is made of or lined with a material that will not react with acidic ingredients such as tomatoes, citrus juice or vinegar. When using a pan that is not nonreactive it will result in an “off” flavor and an unappealing, but harmless, darker coloring of of the food. This is why a nonreactive pan is essential when cooking certain foods.
The most common nonreactive pans are made of anodized stainless steel but they can also be made from enamel or glass. On the flip side, reactive materials include nonanodized stainless steel, unlined copper or cast iron. Cast iron is the least problematic of the three as it can be used to prepare acidic foods only if the food is not left in the pan for an extended period of time.
When liquid is maintained at a temperature just below a boil, it is called a simmer. When there are tiny bubbles barely breaking the surface it’s considered a “gentle” or “low” simmer. If the bubbles are larger and moving faster, it’s considered a “rapid” simmer.
Simmering cooks food gently and slowly, perfect for delicate foods such as fish or fibrous root vegetables like potatoes. Keeping potatoes at a simmer allows them to cook more evenly.
When liquid is brought to a boil, the bubbles will be numerous, large, and consistently breaking at the surface. At this point, the liquid will also quickly evaporate.
Because boiling keeps food in motion it helps to cook it quickly and prevent it from sticking to itself which is ideal when cooking pasta. Tender green vegetables also do well with boiling because it helps to maintain their color and flavor. Lastly, because boiling causes speedy evaporation of liquids it’s also the best method to use when trying to reduce sauces.