The dwarves in Dwarf Fortress have their origins in Norse mythology. Mead has a lot of significance in Norse mythology, so I find it unacceptable that Dwarf Fortress has no mead!
In fact, I have several problems with the way Dwarf Fortress deals with alcohol:
1. Though fungus is a necessary part of fermentation, it can not itself, as far as I know, be fermented into alcohol. I might be wrong, since I couldn't really find any info comfirming this, and I suppose we could just say that the fictional mushrooms in Dwarf Fortress do produce fermentable sugars, so it isn't really a big issue for me.
2. All types of alcohol in Dwarf Fortress are made in a "still". A still is for making distilled liquors, so it would make sense for rum and whiskey, but not for beers and wines and the like, which are not distilled. To be honest, I'm not sure what word would be ideal for this building. Beer is made in a brewery, wine in a winery, mead in a meadery... I'm not aware of any general term.
Similarly, the job for creating an alcoholic beverage in this building is "Brew a drink". Technically this would only refer to making malted beverages such as beer and ale.
3. The drinks are created almost instantaneously. In reality, fermentation takes at least a couple weeks, depending on the type of drink. Perhaps a wort/must barrel should be created instead, which is racked or distilled after two to four weeks, becoming the final product.
4. While grapes do not require the addition of water to become wine, creating beer does require water. The fact that you don't need water to produce any of the drinks in Dwarf Fortress makes me wonder... Is longland grass really juicy?
But the biggest problem I have is the lack of mead!
Perhaps beehives could spawn outside similar to the way cave spider webs do (but not so plentifully). A dwarf can gather it, turning it into a honeycomb object, which can be processed into liquid honey and beeswax (which would become useful when candles are implemented). The brewer would turn honey and water from a bucket into the must that would become mead.
Also, I imagine that, since the ingredients for mead come from the outdoors, some people might be inclined to suggest that mead be more of an Elven/Human drink than a Dwarven one. I disagree with this on the basis that the Mead of Poetry, from Norse mythology, was created by dwarves.