We just moved a couple months back and not everything has been found, namely the heating pad. I did get the books I ordered from the library and was able to make a good find of info. The first book,
The Incredible Secrets of Mustard, was worthless for my purposes. The second book which was simply titled,
Mustard, by Janet Hazan gave me what I was looking for. As I was casually flipping through the book I read an anecdote that said, "The heat in mustard comes from the enzyme myrosin, which is released when the seed is crushed or bruised and mixed with a liquid."
Now that I had the name of the enzyme I did some internet searching that led me to an article that had three really good nuggets of info. Article here:
http://www.ediblecommunities.com/vancouver/Recent-Articles/cutting-the-mustard.htm
The article is worth a read, it's short and entertaining but here are the three nuggets excerpted:
1. "the darker the seed, the more pungent the finished product."
2. "cold liquids start the reaction; warm or hot liquids arrest it. For maximum hotness, make sure the liquid you add to the ground mustard is cold. Add warmer liquid to limit the potency." (sorry grisell, no specific temperatures were mentioned)
3. "acid neutralizes the decline in spiciness. As time passes, the spiciness of your mustard will fade. Taste it every couple of minutes, and when you find a level of heat you like, mix in the acid of your choice, usually a type of vinegar. This will stop the pungency from dissipating any further." (this last one hit me right across the noggin as it's exactly what I did with my recipe. I added the cider vinegar at the same time as the other ingredients and barring any future heating I should expect that it's going to stay pretty close to it's current potency. I read an actual scientific study that mentioned a highly refined version of the enzyme held it's potency for over 53 days)