Whether you make your own barbecue sauce from scratch or buy a commercial product, the thicker the sauce is, the more likely it is that it will thoroughly coat the meat being barbecued. There are a number of ways to change the consistency of a sauce. By heating the liquid for a period of time, you reduce the amount of moisture in the sauce without adding any further ingredients. Alternatively, you could use a thickening agent, such as cornstarch or flour.
Pour the barbecue sauce into a pan and place it on the stove.
Set the burner to medium heat and bring the sauce to a boil.
Reduce the heat under the sauce to low. The goal is to allow the barbecue sauce to simmer long enough for some of the liquid to evaporate.
Stir the sauce continually as it simmers to avoid burning it.
Remove the pan from the burner once the barbecue sauce reaches the desired consistency and allow the sauce to cool to room temperature.
Add the cornstarch to the cold water using a ratio of one part cornstarch to four parts flour.
Whisk the cornstarch mixture with a fork to thoroughly dissolve the powder. The resulting liquid should be the consistency of pudding or thin paste.
Pour your barbecue sauce into a pan and heat it on a low temperature setting.
Stir the cornstarch slurry into the warmed sauce 1 tablespoon at a time until the sauce is your preferred consistency.
Combine flour with cold water in a ratio of one part flour to two parts water.
Stir the ingredients vigorously with a fork until the mixture develops into a thick liquid. Continue stirring until all of the lumps from the flour are dissolved.
Fill a saucepan with the barbecue sauce. Place the pan on the stove and let the sauce simmer over low heat.
Stir in the flour mixture 1 or 2 tablespoons at a time while the sauce simmers. Add as much of the flour paste as you need to thicken the barbecue sauce.
Remove the pan from the stove once you have the proper texture for the sauce and allow the mixture to cool.