Mishna Shabbat 4

Read it in Hebrew has the full Hebrew text. It opens a new window so you can compare the English & Hebrew.

1. What what may food be covered to keep it hot? To begin with, let us first discuss what may not be used: husks , manure, salt, lime, sand (whether wet or dry); furthermore, do not use straw, grape skin, fluffy pulp , or fresh herbs ; having said so, dry herbs are fine , as are garment fabrics , ground-fruits , the wing of a dove , sawdust, caulking made from refined flax; Rebbe Yehuda permits unrefined flax in the caulk but not refined flax.

2. Animal hide may be used to cover and may be removed and replaced as needed ; not so for wool shearings, which may be used but not removed or replaced . How? By what action? The lid is removed and the shearings fall away . Rebbe Elazar Ben Aazr’ya explains it this way: the top is bent on its side and the strands fall away so that the food can be removed but not put back in. The sages respond: the food may be removed and replaced . The food must be covered before the onset of Shabbat. If this was done and the cover came off? Replace the cover. It is also fine to place a jug beneath the cushion .