Ancho chilies are dried ripe poblano peppers. Ancho chilies, like fresh poblanos, are generally low in heat, with a distinctively sweet and raisin-like fruity flavor.
Mulato chilies are dried variety of poblano pepper, picked when very ripe. Mulato chilies are moderately hot, with a sweet, fruity, slightly smoky flavor. They’re highly appreciated for the distinctive chocolate/cherry/licorice notes that they impart to a dish.
Pasilla chilies, are dried, ripe, chilaca peppers. Pasillas are elongate, thin, and tapering, with wrinkled, nearly black skin. Their flavor is fairly similar to that of an ancho chili, with raisin and coffee notes. They also tend to be a little hotter than ancho chilies.
Above from http://www.diversivore.com/guide-to-mexican-chili-peppers/
The correct spelling for the pod of the capsicum plant is chile. This was actually read into the congressional record by Senator Pete Domenici of New Mexico. To paraphrase, chili with an “i” is the red stew that is made in Texas. Chile with an “e” is the fruit of the capsicum plant, which is the major agricultural product of New Mexico. From here.
The Holy Trinity of Mexican Chili Peppers:
“The Holy Trinity” is a tasty blend of 3 Mexican Chili Peppers. They are a staple in any Mexican kitchen, and are used in many traditional dishes.
Ancho:
Dried, ripe Poblano Peppers, Ancho Chilies have a distinct sweet, fruity flavor and are lower in heat than many other peppers. They are a staple in traditional Mexican dishes, such as Mole sauce and Tamales.
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Mulato:
Mulato chilies are also a dried Poblano pepper. However, they are picked when very ripe, so the flavor is distinctly different from Ancho chilies. They have moderate heat, are still sweet like an Ancho, but also exhibit a smokey flavor. Mulato Chilies are the hottest member of the Holy Trinity and are extremely popular in Mexico.
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Pasilla:
The Pasilla Chile, or “Chile Negro,” is a dried Chilaca pepper. They are mildly hot, with flavors of sweet raisin and coffee. Pasilla chilies are used in a lot of meat and savory dishes, particularly in sauce.
