If you're looking to add flavor to your barbecued meats and poultry, but you're not interested in using a barbecue sauce, a rub is the way to go.
A rub is a blend of seasonings, spices and herbs that are mixed together and then applied to the surface of a piece of meat or poultry before smoking or barbecuing.
And what do we mean by barbecue? In this context we mean long, slow cooking at a low temperature, like 225 F, especially over wood coals. This is totally different from grilling, which although it also takes place on a grill, utilizes high temperatures and short cooking times.
And using a dry rub for grilling will cause the rub to burn (much like when using barbecue sauce during grilling). So that's rule number one: Use rubs for barbecuing and smoking, not grilling.
What is a Rub?
Beyond that, the only other rule is that a rub combines salt and sugar. You can add heat and aromatics to your heart's content, but at a minimum, a rub is a blend of sweet and salty flavors.
And we should also specify that a rub is dry. Yes, there are so-called wet rubs, which include liquid ingredients like lemon juice, Worcestershire sauce, molasses and so on. A wet rub isn't quite a sauce; it's more like a thick paste.
With rubs, the ingredients are applied directly to the meat, and they adhere to it either by way of the meat's natural surface moisture or by brushing it with oil first.
Nevertheless, wet or dry, BBQ rubs follow the same rule of salty and sweet plus whatever else. Note too that wet rubs are really the only way to include sour flavors like vinegar or citrus in a rub, and these flavors can sometimes be desirable.
Building a BBQ Rub: Start with Salt and Sugar
So start with a cup of Kosher salt. For Morton's Kosher salt, a cup is about 250 grams, whereas Diamond is more like 200. So make sure you weigh it to make sure, and then simply add an equivalent amount, by weight, of sugar. Whether you use white sugar or brown sugar doesn't matter as long as it weighs the same as the salt. Note: A sweeter rub will work with pork shoulder or pork ribs, but you might want to experiment with using less sugar for your brisket or tri-tip.
By the way, we're not going to worry about weighing everything, but with Kosher salt, the coarseness is what determines how much a given cup will weigh, and since the salt and sugar are the base, it's a good idea to get those quantities right. And by the way, don't use table salt (i.e. ordinary salt-shaker salt). It's got a metallic flavor that is more noticeable in larger quantities.
Adding Heat and Color
Next, most rubs will feature a generous portion of paprika. You can use smoked paprika, which will impart a lovely wood-smoke flavor to your rub, or plain. But with a cup each of salt and sugar, you can go with anywhere from 1/2 to 1 cup of paprika and not go wrong.
And with this ratio, 1 tablespoon of cayenne pepper is probably about right to add a medium amount of heat. Remember, you're not eating the rub by itself. It's being distributed across the surface of the meat. Chipotle powder is another lovely way to add heat, color and smokiness, since chipotles are smoked chiles.
Finally, black pepper will also impart a bit of heat. You can add more or less, but if you're going with 1 tablespoon of cayenne, then 1 tablespoon of ground black pepper is probably about right. Ideally you'd use freshly ground but grinding that much pepper can be tedious so it's not the end of the world if you use the preground kind.
Finish with Aromatics
Finally we have aromatics, which are a broad category of ingredients including garlic and onion powders, cumin, mustard powder, as well as dried herbs like oregano. You'll use a smaller quantity of each of these, but when combined they could easily make up 1 cup overall (assuming a base of 1 cup of salt and 1 cup of sugar).
These are your basics, and you can absolutely make an absolutely magnificent BBQ rub using just the ingredients that have been mentioned so far.
But you can also branch out, once you're ready to do some experimenting, into ingredients like celery seed, caraway seed, ground ginger, and spices such as allspice and coriander, as well as herbs like thyme, rosemary and parsley.
How Much Rub to Use
It's common to see spice rub recipes that are reckoned in terms of how much rub to use per pound of meat. Which is not a terrible way to calculate, but bear in mind that you're only seasoning the surface of the meat, and the surface area of a piece of meat does not exactly correspond to its weight. Therefore it's a fairly inaccurate way to calculate.
What you want is simply to cover the entire surface of the meat. When no more will stick to it, and the excess simply slides off, you've applied enough. But since BBQ rub keeps for several months when stored in a cool, dry place, you might as well make plenty and store what you don't use in a ziploc bag or other airtight container.
It's not a bad idea, though, to label your container with the ingredients you used and in what quantities. That way when you go to replicate it later, or even if you want to modify it, you'll know what was in it to start with.