Daily Halacha: What Foods May Be Rewarmed on Shabbat?

Is it permitted to heat water that was already heated and then cooled before Shabbat?

In halacha (Jewish law), there is a concept called bishul achar bishul—“cooking after cooking.” This means that once something has already been fully cooked, warming it again is generally not considered cooking.

This rule mainly applies to solid foods, but for liquids, the halacha is usually stricter. However, if a food or drink gets worse when cooked again rather than improving, it may be reheated on Shabbat, even if it reaches the temperature known as yad soledet bo (hot enough that the hand would pull away).

So according to the basic halacha, it is permitted to heat water on Shabbat if it was already boiled before Shabbat (on Friday) and then cooled down.

Is it permitted to place solidified food on a hot plate (plata)?

Some foods naturally start as dry, such as chocolate or jam, and these may be placed on a hot plate even if they will soften or become moist and reach yad soledet bo temperature. Since they are considered dry foods, this is permitted.

However, it is not allowed to place gravy or sauce that has solidified in the fridge onto a hot plate. These types of foods started off as liquid and became solid from refrigeration. Reheating them would be like turning them back into a liquid which is considered cooking on Shabbat and is not permitted.

This halacha is explained in Shulchan Aruch.

From “Ach Tov VaChesed – Daily Halacha” by Hidabroot