The Romans made wine two ways: by treading on the grapes or by pressing it. Treading was the preffered method and produced the higher quality wine. Pressing would be done three times, and each time the juice would be syphoned off to produce an increasingly coarser wine. This third pressing would have needed watering down because it would have been virtually vinegar. It is also this third pressing that would have been offered to slaves as a treat.
The freshley pressed juice would then be stored in a dolium which would have been partially buried in the ground. It was in the dolium where fermentation took place from between two to four weeks. To sweeten the wine they boiled a portion of the juices to bring out the natural sugers and then add it to the dolium halfway through fermentation. The finished product with have been closer to a modern Madeira. To lessen the acidity the consumer would sometimes add chalk or marble dust.
Unfortunatly grape varieties are not usually named in the sources with the Amenean - not extinct - grape being an exception with Virgil and Pliny singing it's praises.
If Gin was Mother's Ruin of Victorian England, wine deserved the same title in Rome. Women were forbidden to drink wine, yet that didn't stop women being portrayed in plays as drunkards and alcoholics. And we all know how closely art reflects society.
Caligula was said to have drank wine unwatered which would go someway to explaining his eratic behaviour. I've even heard it be said that his mysterious illness was as a result of alcohol poisoning.