I tried several things with mustard powder and ground mustard seeds. I cooked with it, made several teas boiled for various times and cold steeped it in some Duvel.
Cooking with it would produce a huge and savory mustard aroma for about 1 minute of sauteed heat time with stir fried veggies. Then it would disappear completely and leave behind very little flavor or aroma.
Boiling hot steeps produced minimal flavor and aroma with 15, 10, 5 and 0 minute boils followed by a fast cool. Cold steeping in beer produced a nice sweet mustard aroma like honey mustard after 24 hours and a light mustard flavor. Cold steeping is the method I'll use for this beer.
Mustard powder produced better results than seeds with less effort. I'll add mustard powder to the primary after fermentation is complete and bottle the next day.
Thanks erockrph for suggesting the cold steep and making me think about the aromatic and flavor volatility of mustard powder in the presence of heat and thanks again to reverseapachemaster and troybinso.