In certain circumstances the Sages forbade leaving food on a fire from before Shabbos, out of fear that one may come to increase the flame on Shabbos in order to quicken the cooking of the food.

The Rabbinical restriction only applies in specific scenarios. It depends on:

1. The type of oven used. [To be discussed in Halacha 3]
2. The status of the food: raw versus cooked. [To be discussed in Halacha 5]
3. The form of cooking that is being done, such as cooking in a pot or roasting over a fire, or baking bread as will be explained.

Concepts:

• Shehiyah: Leaving a food on a fire over Shabbos, having been placed there on Erev Shabbos for the Shabbos meals.
• Ben Drusaiy: The name of a robber who would eat his food prior to it being fully cooked. The exact definition of how much cooking is required for it to be considered “Ben Drusaiy” is disputed, of which the ruling is that it Lechatchilah refers to a food that is at least half cooked. This will be discussed further in Halacha 5B.
• Mitztameik Veyafeh Lo: Further condensing is beneficial for the owner.
• Mitztameik Vera Lo: Further condensing is damaging for the owner.
• Bichideiy Sheyasu: Amount of time it takes for one to cook a certain food.
• Gerufah: The removal of the coals from the oven
• Ketumah: The covering of the fire.
• Yad Soledes: An area where food can heat up to approximately 110 Fahrenheit.

Practical summary of how to prepare the Blech Erev Shabbos:

• Below is provided a quick summary of the Halachas explained in this section. For the full details please refer to the relevant Halachos and Q&A written in this section.

It is forbidden to leave less than half cooked food on an open flame into Shabbos. This law created the use of a Blech. The blech effectively covers the fire and allows one to leave even less than half cooked foods on the fire into Shabbos. In most cases the foods are in any event fully cooked and a blech is hence not needed. It is customary however to place a blech over the fire even in such a case, as this allows one to be allowed to return foods to the fire on Shabbos in case of need. [See “The Laws of Chazara” for more information!]

Covering knobs: It is proper to cover the knobs of the stove in addition to covering the fire. Today there are blechs available that contain a side metal addition which is used to cover the knobs. Alternatively one can place tinfoil over the knobs.

Electric plates: If one uses an electric plate to keep his food hot over Shabbos then if the electric plate does not have alternate settings of heat, it does not need to be covered even if the food will not be half cooked before Shabbos. If it does have alternate settings of heat then it must be covered for one to be allowed to leave less than half cooked food on it into Shabbos.

Ovens: One may leave food which is at least half cooked in a lit oven into Shabbos. One may not leave less than half cooked foods in an oven unless the inside of the oven is properly covered. [See “The Laws of Shehiyah” Halacha Q&A 3 for details!]  One must beware not to open an oven while it is off if it is temperature based. [See “The Laws Of Cooking” Halacha 15]

When to set up the blech: The blech is to be set up together with the food with enough time for the food to heat up if the food were to be cold. Meaning even if the food is currently hot it is to be placed on the Blech with enough time for it to become hot if it were to be cold. In a case of need one may set up the Blech any time before Shabbos even if the food is cold.

If one does not have a blech or electric plate: If one does not have a blech or electric plate for Shabbos he may still leave all his food on an open flame before Shabbos, so long as the food is half cooked by the time Shabbos enters.