When he is the right amount of drunk (green outline) he gets chatty and can be persuaded to give you some of his top quality barley for the Brewday quest 'Brell's Everlasting Brew'. To get him into that state:
1. Sober him up by buying him a cup of strong black a coffee.
2. Count the dwarven ales you have Dwayne serve him, until he gets agressive in his tone or he gets a green outline (lets you skip to step 6).
3. Sober him up again.
4. Now order him one dwarven ale less than what made him agressive.
5. Then start getting him some gnomish spirits until he gets chatty (green outline).
6. Now talk to him about his barley.
He serves the drinks to Jimmy:
- A dwarven ale will get him drunken quickly.
- Some gnomish spirits will get him drunken less quickly but he can't take many of them.
- A cup of strong black coffee will sober him up so you can try again.
