Chili powders are not interchangeable. The reddish-brown powder often found at stores or in the pantry, labeled "chili powder," may look much like ancho chili powder, but the two tastes are considerably different. Ancho chili powder is made from ancho peppers, which are the sweetest of the chili peppers; it is also relatively mild compared to powders made from other chili pepper varieties. Besides Mexican cooking, ancho chili powder also can be sprinkled directly on foods, much as salt and pepper are used.
Traditional Chili Powder
The reddish-brown powder sold as chili powder is a blend of spices that season chili and similar dishes. Dried ground chilis are only one ingredient. Most traditional chili powders use powdered ancho or jalapeno chilis as their base, then add cumin, oregano, garlic and salt. The type of chili used in chili powder is what determines how hot it will be.
Ancho Chili Powder
Ancho chili powder is a pure chili powder, made only from dried chili peppers with no other ingredients added. Fresh poblano peppers are dried, creating the flat, wrinkly, heart-shaped ancho pepper. When finely ground, the dried, reddish-brown ancho peppers produce a sweet, mild, slightly smoky seasoning. Ancho chili powder is commonly used in authentic Mexican dishes such as tamales.
Chili peppers are rated for the degree of hotness they produce according to the Scoville Scale. Ancho peppers and the resultant ancho chili powder are very low on the scale, at only 1,000 to 2,000 Scoville heat units. This is only slightly higher than a standard green bell pepper, rated at zero on the Scoville scale. Jalapeno peppers, in contrast, typically rate between 2,500 and 5,000 units and spicy Cayenne or Tabasco peppers range between 30,000 to 50,000 units -- a substantial difference.
If you are preparing a favorite Mexican dish and don't have ancho chili powder, don't just use whatever chili powder you have available without scrutinizing the label first. Chili powder made from pure ground pasilla or Coronado peppers is the closest in heat and flavor to ancho chili powder. If you only have a blended chili powder based on jalapeno or another pepper that is considerably hotter than ancho peppers, use a much smaller amount to avoid making the dish much hotter than is called for in the recipe.