Cheres - Pyrex

QUESTION: According to those opinions that maintain that glass does not absorb, does this mean I can use a Pyrex baking pan for both milk and meat?

ANSWER: Even if glass utensils do not absorb, it is still not advisable to use them for both milk and meat, since they might have residue from the previous use, and one might forget to scrub them completely clean. Regarding glass which is used directly on the fire or in an oven, such as Pyrex baking pans, there is a disagreement among poskim as to whether glass retains its non-absorbent status. Rav Ovadya Yosef (Yechaveh Daas 1:6) writes that for Sefardim, even glass baking pans which are used directly on the fire can be scrubbed clean and used on Pesach since they do not absorb. However, the Tzitz Eliezer (9:26:2) cites many poskim, including Rav Shlomo Kluger and the Maharam Schick, who write that we must assume that glass which was used on the fire absorbs. Accordingly, it most certainly may not be used for milk and meat even if it was carefully cleaned. Rav Belsky said that he heard from Rav Yaakov Kamenetzky as well that glass utensils which were used on the fire absorb and should not be kashered even in cases of significant loss.

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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.