803. Sifting

Shabbos 21:32

Sifting is a category of prohibited labor. We may not sift straw in a sieve, nor may we place a sieve full of straw up high so that the chaff will fall as this is like sifting. We may put straw in a sieve to carry to an animal's trough. Even though chaff falls away in transporting it, this is not problematic because it is not a person’s intention.

Shabbos 21:33

One who makes a mixture out of particles and water is liable for kneading. One may therefore not make a mixture using a large volume of roasted flour out of concern that one may come to knead unroasted flour. One may mix roasted flour a little bit at a time. Regarding grain that has not matured to a third of its growth, which is roasted and ground coarsely like sand, one may mix a large volume with things like vinegar all at once so long as the resulting mixture is soft. If it is firm, it is prohibited because of its similarity to kneading. Even for a soft mixture, one may not follow the normal weekday procedure. Rather, one must first put in the grain and then the vinegar.