Here’s a nice little article on the halakhot that surround making kiddush on whisky instead of wine. The author, R’ Ari Enkin, observes in his second footnote that some permit whisky on Friday night as well, while others forbid it. His source for that is the Shulchan Arukh (Orach Chayim 272:9), which gives no evidence either way. It’s not alluded to in this article, but there’s actually a cute story that surrounds the impermissibility of using whisky for this purpose.
In Jeremiah 11:16, the prophet likens Israel to an olive tree. There are a couple of midrashim (Shemot Rabbah 36:1 and Shir haShirim Rabbah 1:21) that explain this in relation to olive oil: just as olive oil when mixed with other liquids always remains distinct, so too does Israel – despite being mixed with other nations – always maintain its integrity; just as olive oil always floats towards the surface, so too does Israel always come out on top.
There was a 17th century scholar named R’ Yaakov Moshe ben Avraham Helin who authored a commentary on Midrash Rabbah called Yedei Moshe. In it, he credits an observation to his brother-in-law, Rav Yitzhak – the Av Beit Din of Krakow. The observation is this: if you pour olive oil into whisky, the oil sinks to the bottom. Surprisingly, this is actually true: the gravity of pure alcohol is about 0.8 and oil about 0.9 (a measure of density with respect to water, water being measured as 1). If we consider the non-alcoholic parts of whisky to be water, a heavier oil could easily weigh more than 40% alcohol.
What to do? The midrash says clearly that oil always floats to the surface when mixed with other liquids, and here we have a case where that is patently incorrect. Rav Yitzhak’s suggestion? Whisky is not a liquid (!!). And not only that, but whisky therefore cannot be used for kiddush on Friday night, since the halakhot of kiddush demand of us that we use a liquid for that purpose.
In his commentary on Orach Chayim, R’ Avraham Gombiner notes some of the reasons held by people who allow the use of whisky (Magen Avraham, OC 272:6), although he doesn’t mention any of the reasons held by those who reject it. In his commentary on Magen Avraham, R’ Shmuel haLevi Klein fills in the gaps (Machatzit haSheqel, OC 272, s.v. ונ”ל דא”מ על יי”ש). Believe it or not but he actually quotes the Yedei Moshe, who rules that whisky isn’t to be considered a liquid, although he does conclude that we don’t learn halakha from such stories. To those of you who are interested, the following is the relevant part of his text:
ובס’ ידי משה על מדרש רבה כתב ראיה בשם גדול א’ דע”כ יי”ש לא מקרי משקה מדאמרינן במדרש למה נמשלו ישראל לשמן מה שמן עולה על כל המשקין ר”ל אם תתן שמן על כל המשקים השמן צף למעלה כן ישראל יעלו על כל או”ה. וביי”ש אם נותן לתוכו שמן, השמן שוקע למטה. וא”כ על כרחך אינו בכלל משקין לפ”ד המדרש הובא גם כן בספר ת”ש אלא דסיים שאין למידין הלכה מפי אגדה
“And in Sefer Yedei Moshe on Midrash Rabbah, he writes a proof in the name of a certain sage that if so, whisky (יין שרף) is not to be considered a liquid, since it says in the midrash: Why is Israel likened to oil? Just as oil rises above all liquids (which is to say that if you place oil in any liquid, the oil will float to the surface), so too will Israel rise above all the nations of the world. But with whisky, if you place oil into it the oil sinks to the bottom. If so, you are forced to say, according to the manner of midrash, that it is not in the category of “liquid”. This is also brought in Sefer T.S. (?), which concludes however that we don’t learn halakha from such stories.”
[H/T R’ Ozer Alport, who first drew my attention to this Yedei Moshe and the corresponding passage in Machatzit haSheqel. And thank you, Sean, for your insights on the relative density of whisky and water.]