Some side quests are more enjoyable than others, while some can be quite confusing or frustrating. Completing "In Vino Veritas" in Kingdom Come: Deliverance 2 involves numerous small steps and even a side quest within a side quest. Let's break it down.
Begin "In Vino Veritas" by speaking with Casper Rudolf, located at his drink cart on the east side of Kuttenberg City (easily found by proceeding straight from the east gate). He seeks the secret to the monks' exceptional wine. Exhaust all dialogue options to learn about Havel and the book he entrusted to Adleta. This sets the stage for your approach to Havel.
To obtain the book from Adleta, visit her garden in the southeast corner of Kuttenberg's inner walls during the morning or afternoon. Gather five marigolds beforehand. Either find her before her brother, Hugo, arrives, or speak with Hugo to gain permission to talk to her. Maintain a kind demeanor while explaining your need for the book to Casper. You can attempt a skill check to obtain it directly, or offer the marigolds as a gift. Once acquired, read the book from your inventory. Note: Obtaining the book from Adleta is optional.
Alternatively, proceed directly to Havel at his inn in Kuttenberg City. Boost your Charisma to at least 18 (adjust your attire accordingly) and hone your drinking skills. In your conversation with Havel, select the following options: Germany, "Let's do it," "That's a very fine gift," Steinberger, and finally, "It's missing ginger." This impresses Havel, revealing the monastery's secret ingredient. Report back to Casper.
Travel to the vineyard north of Kuttenberg. Initiate the "Under the Straw Hat" side quest by speaking with the recruiter. While not mandatory for "In Vino Veritas," starting this quest allows unrestricted access to the vineyard. Locate Jerome on a bench near the main building.
Enter the main building, turn left, and access the storeroom. Use your lockpicking skills to open the chests and acquire the Sulphur Wicks needed for Casper. For extra Groschen, collect five seedlings from the garden behind the main building before departing.
To complete "Under the Straw Hat," perform tasks such as removing plants and moving sacks, then report to Jerome. Otherwise, return to Casper, delivering the wicks and seedlings (if collected).
This concludes "In Vino Veritas," allowing you to progress to other quests in Kingdom Come: Deliverance 2, or perhaps pursue badge and dice collecting.