In a small bowl, combine beer and mustard seeds. Cover and refrigerate overnight.
Place seed mixture in a blender. Cover and process until chopped and slightly grainy.
Transfer to a Dutch oven. Add the ground mustard, brown sugar, vinegars, salt, allspice and cloves. Bring just to a boil. Remove from heat; stir in vanilla.
Ladle hot liquid into 7 hot half-pint jars, leaving 1/2-in. headspace. Wipe rims. Center lids on jars; screw on bands until fingertip tight.
Place jars into canner with simmering water, ensuring that they are completely covered with water. Bring to a boil; process for 10 minutes. Remove jars and cool.
Editor's Note
The processing time listed is for altitudes of 1,000 feet or less. For altitudes up to 3,000 feet, add 5 minutes; 6,000 feet, add 10 minutes; 8,000 feet, add 15 minutes; 10,000 feet, add 20 minutes.
