Berakhot 140

9:
We now come to discuss the substance of the first item of disagreement between Bet Hillel and Bet Shammai in this present chapter. It concerns the recital of Kiddush on Shabbat and Yom Tov. The Kiddush, [usually] recited over wine, is a declaratory statement made before the festive spread to the effect that the day is holy. Kiddush on Shabbat Eve consists to two berakhot: a berakhah over wine [assuming that wine is being used, as is almost universally the case] and then a berakhah which declares the sanctity of the day. On all festival evenings (with the sole exception of the last day/s of Pesaĥ) a third blessing is added, called Birkat ha-Z^eman [the blessing of the season], known familiarly as she-he-ĥe-yanu. The order of berakhot here described is in accordance with the opinion of Bet Hillel as brought in our Mishnah. (In the vast majority of cases, where there is a maĥloket [difference of opinion] between Bet Hillel and Bet Shammai, the halakhah is in accord with the opinion of Bet Hillel.) The Gemara explains the rationale of this difference of opinion as follows:

I have received several messages concerning the issue raised by Reuven Boxman concerning the nature of the wines in Rabbinic times. You will recall that I had originally explained that In rabbinic times the wine was bottled "neat" and in order for it to be drinkable it had to be diluted with water. Reuven had commented that to the best of my knowledge wine then, as well as wine today, is fermented naturally, and the fermentation process comes to a halt when the alcohol content reaches approximately 12-13%. The only way to get a "stronger" wine is by distillation, which today we would not call wine, but rather spirits, and I don't think that the mishnah is referring to a distilled product. Since I am quite unknowledgable in this matter, I requested assistance.

First of all I checked with all the classical commentators and found that my statement reflected their teachings. For example, Rambam comments on this mishnah: their wine was so strong that it was undrinkable before being diluted with much water.

Andy Berkowitz explains: Wines's alcohol content derives from the sugar content of the grape juice used. Yeast is used to convert the sugar to alcohol and carbon dioxide. The CO₂ is given off as a gas, but the alcohol remains. Different grape varieties and different growing climates produce grapes with varying sugar content. Also, sugar can be added before fermentation to increase the alcohol content. Because high-alcohol wines last longer than low-alcohol wines, the vintners may have intentionally created stronger wines. Today, many wines makers start with grape juice concentrate. Because concentrate weighs less than juice, it is easier and cheaper to transport. It is later diluted. Perhaps the same process was followed in Talmudic times. [I comment about the possibility raised by Andy in his last sentence that it does not seem to be the case: the process of making wine in ancient Israel is described in Encyclopedia Judaica 6:1417-1418.]

Reuven Lerner quotes from a book ["On Food and Cooking: The Science and Lore of the Kitchen", by Harold McGee, published in 1984 by Collier Books)]. In Chapter 9 ("Wine, Beer, and Distilled Liquors"), McGee says (p. 427):

Reuven Boxman's comment regarding the alcohol content of wine is indeed correct. As McGee says on p. 431:

Did the Greeks (and thus the rabbis of the Talmud) know about distillation? McGee seems to think not, and quotes Aristotle, whose Meteorology (Book 2) describes the amazing science of distillation without mentioning wine or beer even once. McGee says (p. 432):