Dear Home Ec 101,
I would like to know why we have to leave the pot uncovered when we are making stock or broth?
Is there any particular reason?
It’s all about ease and evaporation in the case of making stock with the French method. During the first hour of cooking the stock needs to be skimmed several times while simmering to rid the stock of proteins that would otherwise cause the broth to be cloudy. After the stock has been strained and it is simmering the second time, the lid is not used to allow evaporation. This step reduces the volume of liquid, concentrating the flavor.
A secondary reason for leaving the lid off is better temperature control. When the stock is simmering it really should be around the 200°F point. Tiny bubbles may form but they should not break the surface. A covered pot retains more heat making it harder to reach the magic simmering point over an extended period of time.
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