The main ingredients in enchilada sauce are chiles, tomatoes or tomatillos, seasonings, and meat such as pork or beef. Pinto beans, black beans, or kidney beans can be substituted for the meat to make vegetarian enchilada sauce. "Enchilar" is the Spanish verb meaning "to add chiles" and enchiladas are corn tortillas covered with enchilada sauce. The tortillas are usually seared first to add a great smoky flavor to the dish.
Red enchilada sauce uses red chiles and red tomatoes, while green enchilada sauce uses green chiles and tomatillos, which are green. Tomatillo means "husk tomato" and the tomatillo is relatively small in size compared to most red tomatoes. The tomatillo is a staple in Mexican ethnic food and is especially popular in Guatemalan dishes. Tomatillos help to tone down the hot chile flavor of enchilada sauce.
Wilbur Scoville, a German scientist, invented a system of rating the heat in all types of peppers. Scoville units are not totally accurate as they are based on human tasting results which can be considered very subjective. However, Scoville comparisons give an excellent way of understanding the different degrees of spiciness between various chile peppers. The Scoville tests blended chiles with a neutral substance added in gradually increasing amounts until the tester could no longer taste the hot chiles.
The ancho, the guajillo, and the New Mexico chiles are just three of the common types of chiles used in enchilada sauce. While growing and other conditions affect the spiciness of chiles, the ancho and the New Mexico have about 1,000 Scoville units of heat each and the guajillo has about 5,000 Scoville units. The habenero chile is considered the hottest and can have a Scoville rating of 300,000 to 500,000 units. Habenero peppers range in color from green to orange.
Seasonings used in enchilada sauce vary, but cumin, garlic powder, cloves, and cinnamon could be used. Some Mexican cooks say adding Mexican cocoa powder is the secret to the best tasting enchilada sauce. Dried chili powder or canned chiles can be used instead of fresh chile peppers. Dried chiles also work, but need to be soaked in hot water before adding to the enchilada sauce.