We commence with the laws of chazora – returning a pot of food to the stove as part of the Melacha of Bishul. This shiur contains 3 conditions with 2 more to follow in the next issue.

Under what conditions may a pot of food be returned to a blech or hotplate on Shabbos?

The critical issue here is that of bishul – cooking. The halacha is that any food or liquid that is not fully cooked is subject to the issur of cooking. By removing and returning food to the fire several prohibitions might be violated.

Let us take the following example: on Friday night, a family member removes a pot of chicken from the hotplate, which is intended for the Shabbos day meal, takes a portion and returns the pot to the hotplate. If the remaining portions of chicken are not fully cooked, that family member has violated a biblical prohibition of bishul. [Whether or not the chicken returned to the hotplate may be eaten is a separate issue and was dealt with a few weeks ago.[1]]

The additional cooking of partially cooked food is a biblical prohibition. [2] Had the partially cooked food not been removed no problem would have occurred.

Before one may return food to a heat source one must ascertain whether the food is fully cooked.

Rule #1 – food or liquids must be fully cooked prior to being returned to a blech or hotplate.

What if I am not sure if it is fully cooked?

Then it may not be returned to the heat source. [3] Since it involves a biblical prohibition, the rule is safeik d’oraisso l’chumra – a doubt involving a biblical prohibition must be stringently resolved.

What is the next problem?

Food removed from a heat source tends to cool down and returning it to the heat source will inevitably raise its temperature. In certain cases this will also involve bishul – cooking. The Shulchan Aruch rules [4] that reheating a cold cooked liquid involves bishul and is prohibited. [5]

How does one define “cold” with reference to returning liquid to a heat source?

It is a machlokes between the Mechaber and the Rama. [6]

The Mechaber holds that food or liquid below the degree of yad soledes bo is considered cold and may not be returned. We know that yad soledes bo is defined as somewhere between 40°-45°C, 104°-113°F. The problem is that it is possible that this may not be taken as a leniency and accordingly l’chumra (stringently) must be calculated as 71°C, 160°F. [7]

The Rama holds that as long as it has not completely cooled down it may be returned. [8]

Rule #2 – Food [9] or liquids must not have cooled down. According to the Mechaber it must be yad soledes bo and according to the Rama it must not have cooled down.

What is the next rule?

Even when food is fully cooked and hot it may not be placed or returned onto an open flame. [10] The reason is because it is mechzi kimvashel – it appears as if one is cooking on Shabbos. In previous shiurim we mentioned the concept of garuf v’katum – raking coals or sprinkling ash onto coals. The modern equivalent is a blech and hotplate, because one does not regularly cook on them. Accordingly the hotplate must be one that is used for warming and not for cooking. Both these items are considered covered heat sources and one may return pots of food onto a blech or hotplate.

Rule #3 – Food may only be returned to a blech or hotplate.

May one cover the flame on Shabbos?

One may cover the flame on Shabbos with a blech, [11] provided that the blech does not become red hot, as that would be hav’arah – making a fire.

Does the covering not affect the flame beneath the blech?

No, it merely modifies the flame's direction or shape but does not affect the amount of gas escaping the burners.

Thus, even if the pot was removed from an open flame where it was placed before Shabbos, one may cover the flame with a blech on Shabbos and one may then return it provided, of course, that the other conditions have been fulfilled.