Pork shoulder is a cut of meat known for its high fat content, making it an ideal choice for low-and-slow cooking methods like smoking or slow roasting. Preparing this cut typically involves applying a generous layer of dry rub before the meat is exposed to heat for many hours. To ensure the rub adheres properly to the irregularly shaped muscle, pitmasters often apply a thin, uniform coating of prepared mustard to the entire surface of the pork shoulder first. This practice serves multiple mechanical and chemical purposes that enhance the final texture and flavor of the barbecue dish.
Acting as a Dry Rub Binder
The primary reason for applying mustard is its function as an adhesive for the dry rub. Because pork shoulder has an uneven surface with crevices and fat pockets, a simple application of dry spices can lead to patchy coverage or the rub falling off during handling. The thick, paste-like consistency of yellow mustard is suited to create a continuous, tacky layer across the entire surface of the meat.
This thin coating of mustard acts as a “glue,” ensuring that the spice mixture stays evenly distributed on the pork shoulder before it enters the smoker. By holding the rub firmly in place, the meat receives a uniform distribution of flavor and color. Without a binder, a significant amount of the rub can be lost during the transfer to the cooking device or as the meat begins to sweat in the initial stages of the cook.
Developing a Superior Cooking Surface
The compounds within the mustard, combined with the heat and the dry rub, contribute to the formation of “bark,” the dark, flavorful crust on the exterior of smoked meat. The moisture from the mustard helps keep the spices moist long enough for the initial stage of cooking, preventing the rub from drying out and flaking off. This moisture allows the sugar and proteins in the dry rub to interact effectively with the surface of the meat.
As the pork shoulder cooks at a low temperature, the heat drives off the liquid components of the mustard, leaving behind the mustard seeds, vinegar solids, and emulsifiers. These remaining solids mix with the spices and the rendered fat, creating a complex surface layer. The proteins and sugars in this mixture then undergo the Maillard reaction, a chemical process that results in browning and the development of new flavor compounds. This reaction produces the deep, dark color and the robust, chewy texture that defines good barbecue bark.
Flavor and Acidity Contribution
While the mechanical benefit of binding the rub and facilitating bark formation is significant, mustard also contributes subtly to the overall flavor profile of the meat. The distinct pungency of prepared mustard dissipates almost entirely during the long, slow cooking process. Because the pork shoulder is cooked for eight to sixteen hours, the strong mustard flavor evaporates, meaning the finished product will not taste like mustard.
The acidity in the mustard, which typically comes from vinegar or wine, provides a subtle advantage. This acid slightly interacts with the meat’s surface, preparing it to better receive the flavors from the dry rub. More importantly, the residual acidity helps to balance the rich and high-fat nature of the pork shoulder. Although the effect is mild after hours of smoking, this acidic counterbalance works harmoniously with the sweet and savory notes of the rub, enhancing the complexity of the final pulled pork.