Why do we cover (put a lid on) pans and pots when cooking?
Well, certainly one reason is to reduce the splatter - to contain it within the pot instead of having it splatter all over the stove.
However, from a broader perspective, we place a lid on a pan or pot in order to:
- Keep the moisture from evaporating. If we cook mashed potatoes on the stove, but didn't cover, then all of the water could evaporate before we actually got the food cooked to the point where it was tenderized.
- On the stove, it creates a small oven so all of the food is cooked from all sides. The lid will keep the moisture in the pot, where it will collect between the surface of the food being cooked and the walls and lid of the pot. This water vapor will contain more energy than will dry air, so the top of the food is being cooked both by heated air (instead of having the heated air escape up and out of the pot to be replaced by incoming cold air to replace the air that moved up and out), as well as being cooked by the heated moisture in that heated air. So we are cooking the food from all sides, not just from the bottom.
- So why do we cover a pot in the oven, which is already an enclosure? It's because it will allow the moisture to stay in the food's environment instead of evaporating into the oven, and to reduce the splatter inside the oven.
- So why do we use terra cotter bowls to cook some foods in, inside the oven? The clay absorbs heat energy from the surroundings, which it radiates to the food. Since it is closer to the food and surrounds the food, it is possible to more evenly heat the food, while retaining the moisture.