Saw this definition of "midlings" on www.kitchenwitch.com:

Midlings "are the hulls that fall off rice when it is processed for human consumption. It has NO nutritive vale of any kind". It goes further to compare the consumption of midlings to eating wood shavings. If slaves could make something like this tasty enough that their master(s) could not stop eating it, then they were smart enough to have escaped.

Georgia Walker-Adams