I have researched that sweet wines were the most popular in the Roman Empire (mostly on Wikipedia, but in these aspects it seems to be more trustable than in other, more controversial subjects), but what about in Medieval Europe? Was sweet wine still favored in regions that were once part of the Western Roman Empire? Was sweet wine favored in the Byzantine Empire? What about in England and France in the Late Middle Ages (I have a huge interest in these in the end of the Medieval Period thanks to the Hundred Years War)? I would be greatful if you could give both general information and more specific information about certain regions and time periods.
The book I have on the subject is a reprint of an older book from the 1940s, and in and of itself is an interesting product of its time, but should give you a place to start, at least with regards to honey wine. It’s called Brewing Mead: Wassail! In Mazers of Mead: The Intriguing History of the Beverage of Kings and Easy, Step-by-Step Instructions for Brewing It At Home by Robert Gayre and Charlie Papazian. The book notes that “in early society, and right down to the Middle Ages, to drink the wine young, when it was at its sweetest and strongest.” (p. 47) The book provides a 10th Century Welsh account of meads being fermented, then topped off with additional honey as they were consumed. It’s difficult to know for sure what “strong” means by itself, but knowing that things like yeast cultivation and pasteurization are modern inventions, it is likely that additional honey was added back to the must to disguise any unpleasant flavors from poor fermentation. If you want to do additional reading on the subject of historical fermentation, I would recommend books by Dr. Patrick McGovern. I don’t have any handy to further flesh out my response and give you more details, but he has published two books and consults with industry experts to do modern interpretations of historic beverages.