Hmm, I actually think that rather than "beermaking" it should be "Brewing", requiring Pottery (where are you going to ferment the beer in? A pit in the ground? Wooden barrels haven't been invented yet, remember.) In addition, I think it should be handled differently, but it leads me into an idea that's been brewing (no pun intended) in my mind for several months, so allow me to be sidetracked...
Fundamentally, I think, we should add an extra layer of resource harvesting. In addition to certain basic resources directly harvested from the land, we should add something else. The best way for me to explain is to describe it in some degree of detail.
Using the example of Beer, a good idea (in my opinion) would be to do this: for a civilization (for the sake of argument, Belgium) that has access to Grains (Wheat, Corn, or Rice), it can build up to one Brewery for every source of Grains it has access to up to five. Each Brewery provides one source of Beer, much as Hollywood provides five of Hit Movies. Thus, nations with only one source of Grains would not be able to sell their beer abroad, but those that have more could sell their wares to drier places. If we wanted to go further, we could have Monarchy be a prerequisite for building Distilleries, where a civilization with access to one source of Beer or Wine could produce Liquor, along similar rules to Breweries. Just a thought.
In any case, other resources might work similarly:
Cows: For a square with a Pasture and Cows, Workers can build Dairies in addition to the Pasture, which would increase the health benefit of the Cows and allow you to build one Cheesemaker's Shop (what else should I call it?) for every source of Dairy-harvested Cows, up to five Cheesemaker's Shops per civilization, each providing one source of (tradable) cheese. The Dairy and Cheesemaker's Shop would require Pottery and Animal Husbandry.
Textiles: A civilization with access to Textiles (either Sheep or Silk) can build one Weaver's Shop (again, what else can I call it?) for every source of Textiles, up to six (aha!) Weaver's Shops, with prerequisite Pottery. Each provides a tradable source of Cloth. In addition, with Replaceable Parts, the civilization can build up to one Textile Mill for every two Weaver's Shops, each providing an additional source of Cloth, and increasing hammers by 25%.
Leather: A civilization with access to either Sheep or Cows may build a up to one Tannery for every source of Sheep or Cows, up to five Tanneries. Each Tannery provides a source of Leather. Requires Animal Husbandry.
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