Preparing for Havdalah on Shabbos
ANSWER: Rav Belsky, zt”l was asked this exact question. He ruled that if one forgot to put a beer in the fridge before Shabbos they may do so on Shabbos to use for Havdalah. He explained that since one isn’t doing any prohibited act by putting beer in a fridge on Shabbos and one is doing so for the purpose of enhancing a mitzvah, it is permissible. This is comparable to the halacha brought by the Chayei Adam (153:6) that on the first day of Yomtov, you may borrow wine from a neighbor if you will need it on the second day of Yomtov for Kiddush, and you will not be able to borrow the wine at night. Although you are not permitted to prepare from one day of Yomtov to the next, but in this case, since the activity involves no melacha, it is for mitzvah, and it is not obvious that you are preparing for the next day (maybe you want to drink the wine on the first day of Yomtov), he writes that it is permitted. Therefore, one should put the beer in the fridge early in the day so that it could also be suitable to drink on Shabbos, and this way it will not appear that one is preparing for after Shabbos.
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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.