After threshing wheat, one would be left with a heap of debris – mostly chaff – with the desirable kernels mixed in among them. Winnowing involved tossing the mixture into the air so that the wind would carry away the papery chaff, while the heavier kernels would fall back to earth. Zoreh is unlike other selection-based melachot in that it relies on wind power rather than selecting by hand or with a utensil. (See Melacha #7, Borer, and Melacha #9, Merakeid.)
The Rama rules that scattering by wind power is a violation of zoreh even without any aspect of selecting (see Orach Chaim 319:17). Accordingly, blowing dust off of a book or shaking out a cloth into the wind would be problematic on Shabbos. Surprisingly, however, using a spray deodorant or similar aerosol product is permissible as those do not actually use air pressure as a propellant, Rather, the compression of a high-pressure fluid is used to propel another fluid through a nozzle.
This is just an introduction to the concepts of the melacha of zoreh; it is not a substitute for a full study of the halachot.
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