If on Shabbat a person has in his plate a hot, cooked food, such as a piece of meat, and a raw food, such as a raw vegetable, must he ensure that the raw food does not touch the hot food, or may he have them touch one another?
A basic principle in the Halachot of Shabbat states that liquid in a “Keli Sheni” (“second utensil”) cannot effectuate the process of cooking as defined by Halacha. This means that, as a rule, once a liquid is transferred from the original utensil in which it was cooked, one may place raw food into the liquid, since it no longer has the capacity to cause “cooking” as defined by Halacha. In a “Keli Rishon” (“first utensil”), however – meaning, the original pot in which the liquid was cooked – the liquid is capable of cooking raw foods, and it is therefore forbidden to place a raw food item into a “Keli Rishon” on Shabbat.
The Maharshal (Rav Shlomo Luria, Poland, 16th century), as cited by the Tureh Zahab commentary to the Shulhan Aruch (Yoreh De’a 94), ruled that this distinction between a “Keli Rishon” and a “Keli Sheni” applies only to liquids. A hot solid food, however, according to the Maharshal, is capable of “cooking” a raw food even in a Keli Sheni. The Maharshal explains that the reason liquids cannot cause “cooking” in a “Keli Sheni” is because the walls of the second utensil cool the liquid slightly, such that its effect on a raw food cannot be considered “cooking.” However, when one takes a solid food item such as meat from the pot and puts it on a plate, it does not touch any walls and it thus does not cool. As such, it is still capable of cooking a raw food.
Accordingly, it would be forbidden to place a raw vegetable on or right next to a hot piece of meat or kugel on one’s plate on Shabbat, since the meat or kugel would then “cook” the raw vegetable. This is the ruling of several recent and contemporary authorities, including the Mishna Berura (Siman 318), the Kaf Ha’haim Sofer, Rav Yosef Shalom Elyashiv and Rav Shmuel Wosner.
Others, however, disagree. Hacham Ben Sion Abba Shaul (Israel, 1923-1998), in his work Or Le’sion (vol. 2, p. 239), and Hacham Ovadia Yosef, as cited in Yalkut Yosef (Shabbat vol. 3, p. 202), rule that even solid foods are incapable of effectuating the process of “cooking” in a “Keli Sheni.” According to this view, then, it would be entirely permissible to place raw foods or raw spices onto or next to a hot solid food in one’s plate on Shabbat, and this is, indeed, the Halacha.
Summary: Once a food has been transferred from the utensil in which it had been cooked, it no longer has the capacity to effectuate the process of “cooking” as defined by Halacha. Therefore, if one has a hot piece of meat, kugel or other food on his plate on Shabbat, he may place raw foods next to or on the hot food.