A Gentile Using a Timer to Operate an Oven

Taken from Zomet Institute
The Zomet Institute is an Israeli high-tech non-profit organization specializing in IT equipment and electronic appliances designed to meet Halacha.

Question: I recently heard that there are Shabbat timers operated by a Gentile using a method of gramma (indirect action). Thus, a Gentile turns the oven on and off using the timer. In our hotel … in Tel Aviv, we have many ovens which are connected to Shabbat timers. I would like to have more details about the timers mentioned above and to know if they can be installed in our hotel.

Answer: The Zomet Institute does not approve the use of a gramma mechanism for ovens in a hotel. Use of this principle is based on halachic permission in a case of a vital need, and it is suitable for hospitals, old age homes, and similar institutions.

What we approve for use in a hotel is an oven or a food heating cabinet using a timer that has been set before Shabbat begins. The precooked food must be put into the equipment before the heating begins. And even then, this only applies to “dry” food (such things as a main course of dry vegetables must be discussed separately). Cold liquid (such as soup) cannot be warmed by this method, since Shabbat laws prohibit cooking a liquid even if it has already been cooked beforehand.

We are aware that some (?) hotels allow a Gentile to put cold liquids into an oven before the timer turns it on, subject to the approval of the local kashrut authorities.

It should be noted that the Zomet Institute approves the system of putting cooked food into the ovens before they are turned on only if two other conditions are met (this is well known by the manufacturers of the equipment):
(1) The safety switch is deactivated on Shabbat, so that opening the door will not directly influence the operation of the oven.
(2) On Shabbat the buttons and switches on the oven must be covered in an esthetic way and locked.