The melacha of ‘mechabeh’/extinguishing is interesting in the way it applies to the halachos of Yom Tov. Typically, one does not extinguish a flame for the sake of cooking; au contraire – one extinguishes when he is finished cooking! We have learned previously that the ‘mitoch’ principle, which expands the permissibility of doing those melachos common to food preparation (‘ochel nefeh’) to even non-food purposes, does not apply to all melachos. Well, unfortunately, ‘mechabeh’ is one of those it does not apply to! So here’s the problem: Generally, a person who wants to be able to cook on Yom Tov will turn on a burner before Yom Tov begins on a low flame and then raise it when he needs more heat for cooking. This is permissible (barring electrical processes that may be prohibited) under the ‘heter’ (permissibility) of ‘ochel nefesh’. But what about after the cooking is finished – can he simply lower the heat now? Based on what we have just learned, it would seem not, as this would constitute ‘mechabeh’ (i.e. reducing the size of a flame, even without extinguishing it) not for the sake of cooking! Oy! – Does this mean that he leaves the fire on high for the rest of Yom Tov?! This is one of the major issues discussed on this siman. We are about to learn about a major leniency which will prove very useful in this scenario:
Rav Cohen writes: “If food is cooking on a stove and, because the flame is too large, it will burn before it is properly cooked, one is permitted to lower the flame. In this situation, lowering the flame is considered a direct necessity for the preparation of the food!”
Ah! - so, that’s the “trick”: When the pot of food is nearing its cooking completion, don’t take it off the fire. Leave it on and let it simmer a bit more. And if you feel that the fire is too hot, and it may burn the food, lower the flame so that the food will come out just right. Now that the flame is lower, you may take the pot off when you desire, and ‘voila!’ – The fire is lower!
Now hear this, as Rav Cohen continues: “However, some Poskim (halachic authorities) rule that this leniency applies only where the option of lighting a new, lower flame is not available… If, however, it is possible to turn on a new flame (i.e. without creating a totally new fire, such as using a pilot light or igniting another gas jet with a candle etc.), one may not lower the existing flame, but should start a new, lower flame!”
That would seem to limit the permissibility of lowering the flame of the one burner so that the pot does not burn, but wait…
“According to HaGaon HaRav Moshe Feinstein zt”l, it is permitted to lower an existing flame to prevent food from burning even if one could start a new flame instead.” (Ed. A fascinating discussion explaining the respective viewpoints of the two opinions can be found in Rav Cohen’s footnote on p. 102, #6)
Summary: “Extinguishing or reducing the size of a flame is prohibited… on Yom Tov except in situations related to the preparation of food. It is permitted to lower a gas flame in order to prevent food that is cooking on it from burning. Some Poskim permit this only when lighting a new, lower flame is not an option. R’ Moshe Feinstein zt”l permits it in any case.”
A few additional points from Rav Cohen:
“1) Although it is prohibited to extinguish or lower a flame for any purpose other than as an aid to cooking, if a gas flame is causing a room to become uncomfortable hot, one is permitted to extinguish the flame in an indirect manner (by means of ‘grama’/causing). For example, one may place a full pot of water over the flame so that the water will boil and overflow, and thereby extinguish the flame. [Once the flame has been extinguished the gas may be shut off.] This method is permitted only if some of the boiled water will be used for a Yom Tov purpose, such as drinking or washing. Otherwise, it would be forbidden to boil the water in the first place.
2) It is permitted to ask a non-Jew to lower or extinguish a flame for any Yom Tov-related purpose, including one that doesn’t involve food preparation (!) For example, if a room is too hot due to a gas flame, or if the flame is too high for cooking purposes, one may ask a non-Jew to extinguish or lower it. Similarly, if one forgot to shut a bedroom light before Yom Tov, one may ask a non-Jew to shut it off. One may not, however, ask a non-Jew to extinguish a flame simply to conserve the fuel or prevent its waste.” [WARNING: These rulings are for Yom Tov only! One must not draw parallel conclusions for Shabbos; those must be studied separately!]