Strangely enough, I
may have found a much quicker and easier way to complete this long series of quests and get the achievement, but I'll need help to confirm because I'm not sure if I got a friendly and lucky glitch or if that was intended.
So when I wanted to start this quest, I went to the location on foot and came across the "guarded treasure" shown on this screenshot:
In this guarded treasure I found the letter that triggered "Wine Wars: The Deus in the Machina" which is really weird because I hadn't begun the series of quests yet, I hadn't even talked to the PNJs, so I didn't do anything for them etc... but I was able to trigger the quest nonetheless.
Anyway, I decided to track the new quest (so the "Wine Wars: The Deus in the Machina one") so I went to the corresponding location, killed the centipede, got the note and the quest was accomplished without any following quests triggered. I decided to track the original quest again "Wine Wars: Belgaard" and when I arrived to the location, Liam and Matilda were arguing and Geralt took part in the discussion saying that he somehow knew what was the problem, and I directly got the "Wine Wars: Consorting" ; from there I just followed the normal path of the series of quest and ended up getting the achievement.
So in the end I didn't have to go through the "Wine Wars: Coronata" and "Wine Wars: Vementino" and I didn't have to be careful about reading letters, halting the quests at the very right moment, etc, so it's a much quicker and much more "braindead" way of doing the quests because you don't have to think about anything ; that's pretty much straightforward.
It seems weird because this specific way of doing the quests looks intended (according to the conversation Geralt, Matilda and Liam had when I first met them) but I find it hard to believe that no one before me found out about it.
I would like one of you to try what I did to verify if that was just a random nice glitch or if this is just for everyone else, which would save some troubles to all of you:
-First take the "Wine Wars: Belgaard" quest but don't do it
-Then go to the guarded treasure shown on the image, where you're supposed to find a letter that triggers the "Wine Wars: The Deus in the Machina" when you read it.
-If you didn't get any letter there, well that means I got lucky and you can just follow the other solutions to guide you through the quests.
-But if you were able to trigger the quest, then do it
-When it's done, just follow the "Wine Wars: Belgaard" quest, complete it and every other quests you receive after it and you should get the achievement.I hope my wall of text wasn't too confusing for you, please don't downvote the solution untill you've tried, I'm just trying to help here. If my "solution" happens to be wrong after verification, I'll just delete it. Thanks.