In the cheese making process, the milk separates into curds and whey. The question is whether the whey (which is essentially a byproduct of the cheese making process) is included in the prohibition of Gevinat Akum. Rav Moshe Feinstein (Teshuvot Igrot Moshe Y.D. 3:17) rules that it is not included in the prohibition, whereas Rav Eliyahu Bakshi Doron (Techumin 23:466) believes that it should be included in the prohibition. Rav Moshe argues that the whey should be viewed as distinct from cheese as butter is viewed distinctly from milk according to the lenient opinions regarding Chemat Akum. Rav Shmuel Wosner (Teshuvot Sheivet Halevi 4:87) adopts a middle approach and rules that the prohibition applies to whey only when the whey is heated together with the curd at a temperature higher than Yad Soledet Bo (hot to the touch). Yad Soledet Bo is the Halachic defintion of heat in the context of Kashrut and Shabbat and Poskim assert varying opinions regarding the parallel in degrees Fahrenheit– the opinions range from 110–120 degrees (see Teshuvot Minchat Shlomo 1:91:8, Rav Shimon Eider’s Halachos of Shabbos p.243, and Rav Mordechai Willig, Beit Yitzchak 21:pp.178-179). Since Beliah (absorption from food) occurs at Yad Soledet Bo, Rav Wosner reasons that the whey absorbed from the Gevinat Akum and is rendered as forbidden.
Rav Blech reports that the policy of the Orthodox Union is to follow the approach of Rav Wosner using Rav Aharon Kotler’s standard (as reported by Rav Shimon Eider and Rav Moshe Heinemann, as cited by Rav Blech) for Yad Soledet Bo, which is 120 degrees Fahrenheit. Although many would not ordinarily rely on Rav Kotler’s ruling in a context where it serves as a leniency, in this context it is justified because the custom has been in the United States (as mentioned in Rav Moshe’s Teshuva) and Israel (see Binetiv Hechalav p.42) to entirely follow Rav Moshe’s ruling. Accordingly, the OU’s policy represents an upgrade from the previously accepted practice.
