Star-K Kosher Certification

Microwaving in the Workplace
Rabbi Tzvi Rosen, Star-K Kashrus Administrator; Editor, Kashrus Kurrents

In today's office cafeteria a company microwave is prominently seen next to the corporate coffee urn. As the cold winter months approach many office workers look forward to a hot cup of soup or hot chocolate with their brown bag lunch. Can the office microwave be used for general Kosher use?

Q. Are there different types of microwaves?
A. Yes. Regular microwaves, Microwaves with a browning element, Convection microwaves.

Q. What is the difference between these microwaves?
A. In a regular microwave the heat is caused by the movement of molecules in microwaved food. The food itself is not enough to heat the microwave chamber sufficiently, i.e. beyond yad zoledes bo.

In a browning element or convection microwave additional heat is introduced into the chamber from outside sources which heats the food and chamber as well. These ovens have a halachic status of a regular oven while a regular microwave does not.

Q. Does that make a difference?
A. Yes. A browning element microwave or a convection microwave must be treated like a regular oven and food to be heated must be completely double wrapped in leakproof wrapping.

Q. What qualifies as leakproof wrapping?
A. Two Ziploc bags or Saran Wrap.

Q. How can one use a regular microwave?
A. Since the chamber of a regular microwave does not get hot, food can be warmed uncovered if the following criteria are met:

The microwave - the ceiling, floor, and door and walls are completely clean of food particles, spills or residue.
No non kosher food is being microwaved in the microwave at the same time.
The floor or turntable is covered or the food is placed on a thick plate.

Q. What qualifies as adequate floor covering or thick enough plate?
A. A sheet of styrofoam or a styrofoam plate is sufficient.

Q. Can food be warmed double wrapped in a regular microwave if a person does not want to follow the cleaning criteria?
A. Yes.