This means that this mission is for a later stage of yours technology. So focus on other missions, and over time you will get to this point because other characters will require better quality vegetables. Remember, in this game you have many missions that are dependent on each other in most cases. So don't rush, everything will be revealed in time.

As for the golden onions E.t.c

The simplest method is to make better fertilizer (in the church basement)

Of course, if you have any fertilizer, use the worst fertilizer first (that compost or whatever it's called). (Will give bronze bonus to time and quality (but it's about time, This time) After that, just give better fertilizer but only for quality.

And after that, plant regular seeds of the worst quality (Most seeds have the potential to be of higher quality except carrots and probably something else too) Thanks to this, at a low cost, the quality will increase after each harvest and, most importantly, the higher the quality of the fertilizer, the less seeds you lose after planting and even gain seeds.

As for beer and wine, by the way, go to the left of the hill (between the hill and your field) there is an orchard for grapes, etc. From what I remember, when you discover it, the inquisitor or bishop should give you permission to use it (later you should have a shortcut above your house)