In the Torah, wine is mentioned many times, though there is no mention of diluting it. The only clear reference to diluted wine in ancient Jewish sources is negative: “Your silver has become dross, your wine mixed with water.”[4] In ancient Israel, wine was preferred without water.[5]  Hashem would provide “a feast of fats, and feast of lees — rich fats and concentrated lees,”[6] ‘lees’ being shmarim, the sediment
from fermentation. Lees are the most flavorful and strong part of the wine, particularly sweet and alcoholic – more like a fortified port than a regular wine.[7]

Yet if we jump forward to the time of the Mishna and Gemara: wine was considered undrinkable unless water was added?!

In Rashi’s world, wine was drunk neat, and he concludes that wine must have been stronger in the past. We could work with this thesis, except that there is a glaring inconsistency: the Rambam a scant hundred years later shared the opinion of the Rishonim: we require wine for the Arba Kosot to be diluted “in order that the drinking of the wine should be pleasant, all according to the wine and the taste of the consumer.”[8][9] We need not believe that wine was stronger both during the time of the Gemara, and in Rambam’s day — but not for Rashi sandwiched between them.  Indeed, Rambam seems to put his finger on the nub of the issue: the preferences of the consumer.[10]

Today we drink liquors that are far more powerful than wine (distillation as we know it was not known in Europe or the Mediterranean until centuries after the Rambam): cask strength whiskies can be watered down by 4:1 and achieve the same alcoholic concentration as wine – but we like strong whiskies. Wine itself can be distilled into grappa, and we enjoy that drink without adding water. Given sweet and potent liqueurs like Drambuie, it seems quite logical that if wine could be made more alcoholic, we would enjoy it that way as well.

While the Mishnah and Gemara are clear that wine should be drunk diluted, the opinion that wine was too strong to drink came from later
commentators, writing hundreds of years later. In the Gemara itself, Rav Oshaya says that the reason to dilute wine is because a mitzvah must be done in the choicest manner.[11] Indeed, the Gemara itself seems to allow that undiluted wines were drinkable – it was just
not considered civilized behavior. A ben sorer umoreh, a rebellious son, is one who drinks wine — wine which is insufficiently diluted, as gluttons drink.[12] In other words, undiluted wine was drinkable, but it was not the civilized thing to do.

A review of the history of civilizations reveals the origin of the preference for diluting wine: Greek culture. The first mention of diluted wine in Jewish texts is found in the apocrypha: about 124 BCE, “It is harmful to drink wine alone, or again, to drink water alone, while wine mixed
with water is sweet and delicious and enhances one’s enjoyment,”[13] The source, it is critical to point out, was written in Greek, outside the land of Israel.

Greek culture and practices started being influential in the Mediterranean in the final two centuries BCE, and by the time of the Gemara, had become the dominant traditions for all “civilized” people in the known world. When the Mishna was written, for example, all educated Romans spoke Greek, and Latin had become the language of the lower classes. Greek customs were the customs of all civilized people.

It is best for the wine to be mixed with as much water as possible. . . . For both are works of God, and the mixing of the two, both of water and wine produces health, because life is composed of a necessary element and a useful element. To the necessary element, the water, which is in the greatest quantity, there is to be mixed in some of the useful element.[14]

Today, wine is not diluted; the very thought of it is repulsive to oenophiles. But just as in Isaiah’s day diluted wine was considered poor (and concentrated dregs were considered choice), the Greeks only liked their wine watered down.[15] We have hundreds of references to diluting wine in ancient Greece through the late Roman period – ancient Greeks diluted wine that Israelites preferred straight. In Greece, wine was always diluted with water before drinking in a vase called “kratiras,” derived from the Greek word krasis, meaning the mixture of wine and water.[16]   As early as the 10th Century BCE (the same time as Isaiah), Greek hip flasks had built-in spoons for measuring the dilution. [17]  Homer, from the 8th or 9th Century BCE, mentions a ratio of 20 to 1, twenty parts water to one part wine. But while their ratios varied, the Greeks most assuredly did not drink their wine straight.[18]  To Greeks, ratios of just 1 to 1 was called “strong wine.” Drinking wine unmixed, on the other hand, was looked upon as a “Scythian” or barbarian custom. This snobbery was not based solely on rumor; Diodorus Siculus, a Greek (Sicilian) historian and contemporary of Julius Caeser, is among the many Greeks who explained that exports of wine to places like Gaul were strong in part because the inhabitants of that region, like Rashi a millennium later, liked to drink the wine undiluted. This fact leads us to an inescapable conclusion: there is no evidence that Greek wine was any stronger than that of ancient Israel, Rome, Egypt, or anywhere else. Greeks and Romans liked their wine with water. Ancient Jews and Gauls liked the very same wine straight up.[19]  We know that it was the same wine, because wine was one of the most important trade products of the ancient world, traveling long distances from vineyard to market. A major trade route went from Egypt through ancient Israel to both northern and eastern climes.[20] Patrick McGovern, a senior research scientist at the University of Pennsylvania, and one of the world’s leading ancient wine experts, believes wine-making became established in Egypt due to “early Bronze Age trade between Egypt and Palestine, encompassing modern Israel, the West Bank and Gaza, and Jordan.”[21]
[22]

By the time of the Gemara, Hellenistic cultural preferences had become so common that nobody even thought of them as “Greek” anymore; civilized people acted in this way. Rambam would no more have thought having water with wine to be a specifically Greek custom than we would consider wearing a shirt with a collar to be the contamination of our Judaism by medieval English affectations.

Another possible reason why certain peoples preferred their wine watered down[23] is that ancient wine was more likely to cause a hangover. The key triggers for a hangover are identified as follows:

1. A bad harvest. If you are drinking wine that comes from a country where a small change in the climate can make a big difference to the quality of wine (France, Germany, New Zealand), then in a bad season the wine contains many more substances that cause hangovers.

2. Drinking it too young. Almost all red wines and Chardonnay are matured in oak barrels so that they will keep and improve. If you drink this wine younger than three years there will be a higher level of nasties that can cause hangovers. If left to mature these nasties change to neutral substances and don’t cause hangovers. As a rule of thumb, wine stored in oak barrels for six months should be acceptable to drink within the first year. If the wine is stored for twelve months or more in oak barrels, it should then be aged at least four years. Some winemakers have been known to add oak chips directly into the wine to enhance flavors (especially in a weak vintage and especially in cheaper wines); this can take years to become neutral.[24]

In other words, in the ancient world, with less precise agriculture, and minimal control over fermentation – and the common consumption of young wine that was not kept in barrels, the wine was surely “stronger” in the sense that the after-effects were far more potent, meriting dilution.

We can also explain the Rashi/Rambam difference of opinion using cultural norms. Greek culture, which dominated the Mediterranen  and Babylonia for hundreds of years, ceased to be dominant in Gaul and elsewhere in Northern Europe after the decline of the Roman Empire. But in the Mediterranean, region, Greek and Roman customs remained dominant in non-Muslim circles for far longer. Rashi was in France, where the natives had never preferred their wine diluted. The Rambam was in Alexandria, where wine, made anywhere in the Mediterranean region (including Israel) had been drunk with water for a thousand years.