Adding Cold Milk to Hot Coffee on Shabbos
ANSWER: In a previous Halacha Yomis we noted that although food does not usually cook in a kli sheini (a secondary vessel), some foods are kalei habishul and cook easily even in a kli sheini. Since we are uncertain what items are kalei habishul, we avoid placing all food in a kli sheini.
Nonetheless, one may add cold water to a cup of hot tea (if not scolding hot) because it is clear from the Talmud that water will not cook in a kli sheini and is not in the category of kalei habishul. What is the status of milk and fruit juices? Do we treat them as kalei habishul, or are all liquids the same as water? Rav Shneur Zalman of Liadi, the founder and first rebbi of Chabad, wrote in his seminal work Shulchan Aruch Harav (318:12) that all liquids have the same status as water. This would seemingly include milk. Accordingly, it would be permissible to add milk to a cup of hot tea. However, the Mishnah Berurah (318:39) writes that milk may be added to a kli sheini only if it was originally cooked. Apparently, the Mishnah Berurah disagrees with the Shulchan Aruch Harav and does not consider all liquids to be the same as water. (As a side note, although we ordinarily do not reheat liquids that have cooled because “yeish bishul achar bishul bedavar lach”, nonetheless the Mishnah Berurah allows adding cold cooked milk to a kli sheini. Apparently, this is because there is a confluence of two uncertainties: there is minority opinion that allows reheating liquids that have cooled, and the status of milk as kalei habishul is uncertain.)
Is pasteurized milk considered cooked? Typically, milk is pasteurized at 161ºF, and according to Igros Moshe (OC 4:74, Bishul §3) 160ºF is the temperature of bishul. Still, there is a possibility that the pasteurization dipped slightly below 160ºF. Even so, Tzitz Eliezer (14:32) writes that one can add pasteurized milk to a kli sheini because of several considerations. First, many poskim cite the ruling of the Shulchan Aruch Harav that uncooked liquids may be added to a kli sheini. Second, perhaps the Mishnah Berurah (who only allows cooked milk in a kli sheini) does so as a stringency and not as an absolute position. Third, the concern that many foods may be kalei habishul is at most an uncertainty. Fourth, it is unlikely that the temperature of the water in a kli sheini will be greater than the temperature at which the milk was pasteurized, and if so, ain bishul achar bishul will apply even if the pasteurization temperature was less than160ºF. He concludes that since there are so many reasons to be lenient, one may add pasteurized milk to a kli sheini. However, as we noted in a previous Halacha Yomis, there is an advantage to preparing the coffee in a kli shlishi (a third vessel filled from a kli sheni) to avoid the Chayai Adam’s concern of yad nichves (that scalding water in a kli sheini is treated like a kli rishon).
____________________________________________________
The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt"l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.