I'll try toasting them first to drive away any moisture.
Per my research that's a wrong move.
I made some badass mustard earlier this week:
1/4 cup brown mustard seeds
3/4 cup white mustard seeds
2 tsp salt
2 tbs of red wine vinegar
2 tbs red wine
enough cold water to achieve desired consistency
I ground up the seeds in the spice grinder. Then into a blender with all the rest of the ingredients, though I added the vinegar once the mixture was somewhat blended. Blended some more to my vision of what mustard should look like and poured into wide-mouth mason jars. Dated the tops and placed in fridge. Ended up with a respectable 1.5 pints of mustard.
The ice cubes helped keep it cold to preserve the hotness.
Initially it was very bitter, but after a couple days it is mellowing nicely with a very nice heat that lingers. It stays with you differently compared to chile heat. I'm getting a lot of sophisticated flavors dropping out of the heat.
Mustard is now back up there in the top five condiments in the euge household. Currently it's beating out mayo, sriracha and salsa.