Without a doubt, one of the most fundamental tenets of Judaism is Shabbat observance. Our rabbis were very concerned that a person should not violate Shabbat and therefore instituted many safeguards designed to distance a person from even the possibility of transgressing. They had a deep understanding of human nature as well as the circumstances that might lead a person to inadvertently transgress the Shabbat. Therefore, each of their safeguards were put in place to counter a potential weakness that a person might have in a particular area.  The Shabbat blech is an example of just such a safeguard.  
   
    When it comes to cooking on Shabbat, Torah law allows us to put a pot of uncooked food on the flame before Shabbat so that we may enjoy hot fresh cooked food on Shabbat.  Because the actions of cooking all take place before Shabbat, there is no violation of cooking on Shabbat itself. In Halacha this is called shehiyah or literally “leaving” food on the fire. Torah law also allows us to take a hot cooked item off the fire and then return it back to the fire.  As the food is hot and already cooked, this returning does not involve any additional cooking of the food. This is called chazarah, returning the food to the fire.
   
    When examining shehiyah, “leaving” food on the fire, the rabbis of the Mishnah understood that the relatively routine procedure of leaving a pot of food on an open fire could lead to an inadvertent transgression of Shabbat. This is because the average cook is very conscientious about the food he or she is cooking and will constantly check it and adjust the flame accordingly. Before the advent of modern cooking equipment, this meant fanning, stoking or raking the coals. This flame adjustment, whether to make it higher or lower, is, in itself, a Torah prohibition.
   
    To remove this concern, the rabbis decreed that if one wants to leave food on a fire before Shabbat he must do two things:  first, he must make a hekair or reminder in the place of the fire; second, he must reduce the heat of the fire.  Historically, this took the form of either the removal of the coals from the stove thereby using the radiant heat from the stove to cook, known as gerufa, or alternatively, covering the coals with ashes or dirt which was known as ketuma.

    Today, this hekair is accomplished with a piece of sheet metal which we place on top of the stove, directly on the burners.  This piece of metal is refered to by the Yiddish word “blech”.  This blech creates both the necessary reminder and reduces the heat of the flame. It must be noted that there are a few circumstances where one may leave a pot of food on the fire without a blech.  Although these scenarios exist, elaborating on them here would be rather technical and would take us beyond the scope of our discussion.
   
    In regard to chazarah, replacing hot cooked food on the stove on Shabbat itself, our rabbis recognized that any act that looks like cooking will eventually lead to mistakes whereby actual cooking will take place. They, therefore, instituted five conditions for returning a pot of food to the fire on Shabbat. One of these five is that there must be a hekair or reminder in the place of the flame. As with shehiyah, in the past this was accomplished with gerufa or ketuma. Today, this too is accomplished with a blech.  So, practically speaking, this means that in order to serve hot soup from a pot and then put it back on the fire we must first have a blech.
   
    So we see that a blech is the means by which we comply with a necessary safeguard that the rabbis instituted to help keep us away from violating the Shabbat.   As we’ve mentioned before, before using a blech or applying any of the ideas mentioned above, please consult your local halachic authority.