Just thought I'd share...Tried this recipe
for stout mustard from Saveur magazine, and it turned out awesome. I couldn't leave well enough alone and follow a recipe exactly, so I made a few substitutions. Half Pints Brewing's Stir Stick Stout (if you're in Western Canada, you need to try this beer!) instead of Guinness, malt vinegar instead of red wine (because malt vinegar just seemed right), and I substituted coriander for allspice because I didn't have any, and besides being completely different, it seemed ok for the recipe.
If you use a homebrewed stout, you may want to pasteurize or cook the mustard; not sure how live yeast in the mix would go over...
The mustard is awesome on garlic sausage or anything else that involves pork and fat, and actually cheaper to make than it is to buy any of those fancy mustards (provided you get your mustard seed bulk, or from an ethnic market, not in tiny bottles in the spice section).