Long ago someone figured out that mustard tends to lose most of its flavor if it sits in a smoker for a long period of time. However, mustard is a good sticky substance and is perfect for holding dry seasonings on meat. Hence, the method of mustard rubbing meat was invented. There are a couple of ways you can do this but the basic idea is the same. A thin layer of mustard on the surface of meats will hold dry rubs in place while the meat is smoked. This is especially true of ribs.
How to Use Mustard for a Rub
To do the mustard trick you can start by preparing the meat to be smoked, patting it dry with paper towels and then coating it with a thin layer of mustard. And best of all you don't have to use expensive mustard. Cheap, basic prepared yellow mustard works great. Now you can sprinkle your rub over the surface of the mustard. The dry rub will stick to the mustard. All you have to do is be a little gentle with the mustard coating to keep from wiping it off. You can wrap the prepared meat in plastic wrap and let it sit overnight. The vinegar in the mustard actually works to pick up the flavors from the rub and carry it into the meat. From this point, smoke the meat as normal.
The Mustard Tenderizes the Meat
Once the meat has completed smoking and is ready to be served the flavor of the mustard will have almost completely disappeared. The mustard actually works to tenderize the meat and you will notice little more than a thin crust of it over the surface of the meat. In fact, the mustard can help to produce the crust that is so sought after in traditional barbecue.
Another way to do the mustard rub is to simply add your dry rub to enough mustard to coat the meat. In effect, you get the same results as you do with the more traditional method described above.