Beer braised brats are a great summertime BBQ dish. I really like it served with a strongly flavored Guinness mustard on a toasted bun with peppers and onions.
Bratwurst is made from veal, beef, or pork and is great when cooked to 141°F (60.6°C), though you can go a little lower if you prefer. Because the sausage is made up of ground meats, you will want to hold it at temperature long enough to pasteurize the middle of it, usually 2 to 3 hours.
Because the beer is sealed in the bags with the sausage, if you don't have a chambered vacuum sealer I recommend just using Ziploc bags to hold the brats. I prefer to finish the brats by grilling them, but you can sear them any way you want. If you don't grill them, you can roast or pan fry the peppers and onions as well.
Most Guinness mustard recipes just add a few tablespoons of Guinness to store bought mustard, which works fine in a pinch, but this recipe creates the mustard from scratch, filling it full of great Guinness flavor. It needs to be started a day ahead of time and the longer it sits the better it will taste. It will last for several weeks in the refrigerator.
Preheat the water bath to 141°F (60.6°C).
Place the bratwurst into the sous vide bag and add the beer. Seal the bag then place in the water bath and cook for 2 to 3 hours.
Combine the mustard seeds, malt vinegar, and Guinness in a bowl. Cover with plastic wrap and let sit for several hours or preferably overnight.
The next day, add the soaked mustard seeds and their liquid to a blender or food processor. Add the remaining ingredients and process until it is the consistency you desire. The mustard can be refrigerated for several weeks.
Peel the onions and then cut into slices about 1/2" to 3/4" (13mm to 19mm) thick, trying to keep the slices together. You can also thread the onion slices onto a shish-kabob skewer.
Cut the sides off of the peppers, leaving them whole. Salt and pepper the onions and peppers and then drizzle with the canola oil.
Heat a grill to high heat. Add the onions and peppers and cook until they just begin to brown and are cooked through. Remove them from the heat. Once they have cooled enough to handle slice the peppers into 1/2" (13mm) strips and cut the onions in half.
Remove the bratwurst from their bag and pat them dry. Sear the brats on the grill over high heat, about 1 or 2 minutes per side.
Brush the inside of the buns with oil and then grill briefly until they just start to brown. Remove from the heat then smear some Guinness mustard on the buns, add a bratwurst, and top with the peppers and onions then serve.
Adding 0.3 grams of xanthan gum to the Guinness Mustard before blending it helps it hold together better and keep its shape when plating.