What is the halacha regarding using a slow cooker on shabbat?
There are a number of questions involved in using a slow-cooker on shabbat: 1) Is there a violation of the prohibition forbidding “hatmana” (=covering a pot with other material to preserve or to add to its heat) on shabbat? In most- if not all- slow cookers, the top of the inner pot is not covered by another additional covering and even the sides of the inner earthenware pot are clearly raised above the walls of the outer metal pot. Ashkenazim follow the psak of the R’ma (Orach Chayyim 253a) who limits the prohibition against “hatmana” to instances where a pot is totally enveloped by another material. Therefore, for Ashkenazim, there is no prohibition of “hatmana” involved in the use of a slow cooker. 2) Is there a violation of the prohibition against leaving uncooked food on Shabbat eve on an open flame (=“sh’hiyya”)? If you add to the slow-cooker a piece of raw meat just before the beginning of shabbat so that it cannot be ready for the shabbat evening meal this prohibition does not apply (Shulchan Aruch Orach Chayyim 253a). To avoid problems of “hachzara”, do not return the inner pot to the slow cooker on shabbat (for a different opinion, forbidding the use of a crock-pot on shabbat, see Shu”t Minchat Shlomo b-c, 12, 9; see Shmirat Shabbat K’Hilchata ch.1, n.195).