Should I cover food while reheating it in a microwave

microwavereheating

For reasons of time, I like to cook more than one portion of a meal and then reheat a portion in the microwave whenever it's needed.

Aiming for maximum energy efficiency, I wonder if it's a good idea to cover the food with a big ceramic or glass bowl?

Just in case this is somehow relevant, here are my two main thoughts which led me to ask this question:

  • Covering might be good because the developing steam is concentrated in a small volume and gives off more of its heat to the food.

  • Covering might be bad because the bowl partly reflects the microwaves, and therefore a part of the energy never reaches the food.

Best Answer

You do get some reflection of microwaves off a glass or plastic cover (Table 1 here)

    Material    Reflection  Transmission
    Metal       0.88         0.00
    Glass       0.38         0.60
    Plexiglas   0.16         0.83

Don't use metal lids. Neither glass nor Plexiglass plastic absorb much of the beam.

The question then becomes: Does reflection off a lid slow heating more than retaining heat in an enclosed vessel speeds it? Anecdotal, but experience tells me that using a plate over a bowl or a casserole dish cover routinely gives hotter, more uniformly heated food. Probably true for plastic wrap too, but I don't use that in a microwave since I had a piece of it melt on me.

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