COMBINE vinegar, beer, Mustard - Yellow Seed, and Mustard - Black Seed in a small bowl.
STIR, cover with plastic wrap and let sit at room temperature for 8 hrs, or up to 24 hrs.
PROCESS soaked mustard seeds with Horseradish Powder, Applewood Smoked Sea Salt, and sugar in a food processor until coarsely ground and thickened, about 1 min, scraping down sides of processor bowl as needed.
TRANSFER mustard into a jar with a tight sealable lid.
REFRIGERATE mustard for up to 2 months.
Yield: 1 cup
Total Time: 24 hrs
Prep: 24 hrs