Cooking Technique/Science question(?) about pot lids
I am learning to cook and this may be trivial...but...
1)What is the purpose of using a pot lid or not during cooking? Please give an example of things you would cook with the pot lid-less and lid-ded? W
2)Also, what is the purpose of the steam venting hole in the pot lid. Does it relate to your answer to (1) above?
At the most basic level, cooking without a lid allows you to reduce the volume of water in a dish -- letting it cook off as water vapor -- and thus concentrate the flavors of the remaining liquid. This process is called reduction; it can be reversed by adding more liquid. Sometimes -- for example, when finishing pasta in a sauce in a pan -- you do both.
Cooking with the lid off or partially on allows you more control over how rapidly something simmers -- simmering (as opposed to boiling) covers a fairly wide range of temperatures between 185F and 212F, IIRC, and letting steam out helps control inadvertant overheating. A steam vent is like leaving the lid very partially off, without the risk of drips from the lid onto the cooking surface; that being said, I would not want a steam vent that could not be closed.
By contrast, cooking with the lid on recirculates much of the water vapor back into the liquid, and thus retains the moisture balance. Sometimes, one even will put foil over the pot, depressing it a bit, and lay the lid over that to deepen that process. Or even seal the lid with foil or clay. Some lids come with a textured underside that act as drip points.
Use a pot lid when you want to retain moisture. Leave the lid off when you want moisture to evaporate.
Rice cooks by absorbing moisture. By leaving the lid on the pot, moisture does not escape. (Maybe not the best explanation, but you get the picture)
When cooking something you want thickened (like a stew or chili), leaving the lid off will allow moisture to evaporate (which also concentrates the flavor)
The steam vent hole can be used to control the amount of moisture that evaporates and it can also be used to tell when a lidded pot is boiling.
Hope this helps.