In a stainless steel bowl, combine 1/2 cup Guinness, 1 cup malt vinegar, and the mustard seeds. Cover with plastic wrap and refrigerate overnight.
Combine the remaining ingredients in a saucepot and bring to a simmer.
Add the mustard seed mix.
Simmer for an additional 5 minutes, stirring constantly.
Give a couple pulses in a blender and pour into clean glass containers, sealing well.