Distillation equipment is recorded as being introduced by members of an alchemical school in Alexandria in the first or second century CE. Distillation seems to have been known in the Roman world, but was employed for alchemy rather than beverage production.
Arab use of distillation apparatus is dated to the seventh or eighth century CE. There is certainly evidence that Muslim philosophers distilled wine into more potent liquids, but it is unclear whether they produced relatively pure ethanol. Rasmussen notes the “common view is that the Arabs did not find the products obtained from the distillation of wine very interesting” in alchemical terms (Rasmussen 2014). Distillation was still seen as an alchemical process, and was used for producing things like essential oils.
Some improvements in distillation were discovered in Al-Andalus similar to what you have read. Abulcasis Al-Zahrawi (ca. 936–1013) is credited with discovering the necessary cooling technology to produce alcohol efficiently through distillation. Though it is unclear if these innovations spread from Spain directly to Italy and France or from the Muslim world more generally over the next 100-200 years.
The isolation of reasonably pure (95%) alcohol/ethanol is often dated to southern Italy during the twelfth century, though some scholars argue it was isolated earlier by Muslim philosophers. Thirteenth-century Venetian innovations in glass production created more reliable glass vessels for distillation (though it seems these ‘innovations’ largely consisted of combining Roman and Syrian glass production techniques). These improved glass vessels are believed to have been significant in the rapid spread of “aqua vitae” production through Europe from early centers such as Montpellier and Salerno.
‘Aqua Vitae’ was used as a disinfectant, anti-septic, base for medicine, and for a variety of alchemical purposes. But as before, this activity was more medical than gastronomical. Though aqua vitae did lead to the development of early spirits such as Benedictine and Chartreuse. It took several more centuries for distilled alcohol to gain acceptance as a beverage rather than just as a medicine.
As for why Europeans didn’t distill spirits earlier. You equally might ask why people went to the trouble of distillation when they could instead simply drink more of a lower-strength alcoholic beverage. There wasn’t really a concept of high-proof spirits, so no-one was looking for ways to make them. Aqua Vitae emerged first as medicine, and the concept of recreationally drinking these distilled spirits evolved only slowly over subsequent centuries.
I couldn't find any scholarship which speaks to your specific conclusion that it would be “easy” to accidentally discover fractional freezing. But some general things to consider: Prior to the development of ethanol distillation in the twelfth century, earthenware is going to be far more common than barrels as a vessel for containing liquids, and earthenware freezes very poorly. Moisture in the clay can shatter the vessel, even if the liquid inside doesn’t freeze solid. Small vessels of many kinds are likely to rupture if left in freezing temperatures, large vessels like barrels full of beer or wine would represent a valuable product, and are unlikely to be left outside uninsulated.
It is possible, Needham concluded that fractional freezing was discovered in China in the third century CE, based on references to ‘outfrozen’ or ‘frozen-out’ wine.
But I couldn't find any reference to the development of fractional freezing in the West. Other than indications the process was used in the American colonies, with some sources claiming the process was discovered in the American colonies.
Sources
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Can you point to anything that specifically rules out freeze "distillation" as a process available to the Europeans? It's not the same thing as fractional distillation by evaporation, doesn't lead to exactly the same outcome, and isn't necessarily considered distillation (for example, there's a bit of a legal grey area on whether freezing and thawing beer to increase alcohol content is legal in the US for homebrewers who don't have a license from their state to distill liquor), so I can see how a source might say that distillation was unknown to the Europeans even if it were aware of the possibility for freezing beer, cider, etc.
Good question. A look at the traditional temperatures for say, cold-distilling gin (-5 C or 23 F-- which is distinctly below freezing) and the average winter temperatures of Europe outside Scandinavia will probably yield insights on how this could be true.
In 1654, the "spirit-in-glass" thermometer called the Little Florentine Thermometer was invented and used as part of the Di Medici meterological network, trying to standardize measurement of the weather. This is how we know about the "Little Ice Age" from the end of the Middle Ages to around 1850. Ocean temperatures were 1.8 F (1 C) cooler than modern temperatures as of 1996.
For temperatures before then, we must rely on climate proxy records (i.e. ice core samples, marine cores, mollusk growth records, and isotope measurements that replace lack of contemporary temperature records), and there is a Medieval Warm Period (Medieval Climate Anomaly) that lasted from 950 to 1250 AD. Ocean temperatures seem to have been 1 degree C warmer than temperatures as of 1996. This is thought to be the warmest period since the Roman Warm period (250 BC to 400 AD.) until modern times.
Because of the warm currents from the Gulf, much of Europe is spared deep freezing despite at being higher latitudes than most of the USA. The ocean is a considerable heat sink and temperatures tend to fluctuate less near the coast than deeper inland (that is, coastal summers are cooler, and winters warmer), so if the ocean warms, Europe warms.
Olso, Norway, is warmer, being near the ocean, and has average temperatures in winter that hover around the freezing point.
Glasgow, Scotland is cold year-around but even January temperatures average above freezing; it rarely falls below freezing. Even the coldest city in Europe, Reykjavík, Iceland, has an average low temperature in winter of just -2 C. The freezes there usually last no longer than a week-- because it's on the ocean.
The success of using freeze distillation naturally would require living in a locale where you had reliably (and predictably) subzero (degrees C) temperatures for long periods, enough to chill whole barrels and form ice, preferably in shade (since wood will warm in direct sun.)
Most of Europe, especially during the Medieval warm Period, would not have fit this description. Even Moscow is iffy, despite much harsher winters than Western Europe. The average high temperature in winter is around -4.5 C and low temperature is -8 C. This means some days are colder and some days are warmer. Temperatures frequently break above freezing.
Places that do easily fit this description would be Ust-Shchugor, Russia, one of the coldest places in Europe. So if you want to look for evidence of freeze-distillation in Europe before steam distillation, colder spots in Russia (and Poland and neighboring areas) would be best to look... you might not find it, though.
The second part of the issue is that fermentation requires warmth-- lager yeasts can be brewed at 40-54 F, while ale yeasts require warmer temperatures up to 70 F. Red wines are considered best fermented at temperatures between 70-85 F. Yeasts won't work well below 50 F, on average (except for the cold-adapted brewer yeasts.) So you want a place with some temperature variation if you're depending entirely on Mother Nature for both fermentation and freeze-distillation. Good brewers want temperature control for consistency, though!
Cold on demand would not come until long after steam distillation. Cutting and storing ice in icehouses-- i.e. the ice trade-- wasn't really afoot until 1806, well after the introduction of steam distillation (this ice was sourced from Norway and New England, later on also the Midwest.)
So, freeze distillation as far as we know, was mostly and heavily used by American colonists living in much harsher winters where they could indeed leave out barrels of hard cider to ice over on top, and thus distill this way. They called it "jacking" whence our name of "applejack" for apple brandies.