Is it a good or a bad idea to cover food that is cooling? For example I have bolognese cooling in a tupperware container but don't know whether I should cover it and refrigerate or leave uncovered out for a while?
There are two factors to consider, both related to the evaporation of water from the cooling dish:
- Evaporative cooling: if the water vapor can leave the container, the food will cool faster, but may dry out slightly
- Condensation: if the water vapor cannot leave the container, it will condense on the lid, and possibly drip back down onto the food
Modern refrigerators are very powerful, so if a little water dripping back is not a problem (which it would not be for a bolognese for example), go ahead and cover the item and place in refrigerator.
On the other hand, if water dripping back onto the dish would mar the surface (of a pumpkin pie, for example), you will want to cool it without a cover until it is no longer steaming.
When the food you've been cooking involves some kinds of vegetables (cabbage relatives, mostly, and some other green leafy things), then one thing to worry about is the collection of sulphur compounds. If you cover the pan, then you can concentrate some sulfide (not a chemist) compounds that you might prefer to have evaporate out through your vent hood.
You should not cover foods while cooling. It will slow down the cooling and also cause a higher chance of bacteria forming. Best way to cool foods is in a refrigerator or if thats not possible at a cool space in a fairly flat container.