Ancho chilies, are dried, ripe poblano peppers (part of the highly variable species Capsicum annuum). Ancho chilies, like fresh poblanos, are generally low in heat, with a distinctive sweet, fruity flavour.
Ancho chilies are closely related to mulato chilies, which are also a variety of dried poblano. Mulatos are harvested later, and are hotter and more distinctively chocolaty tasting than ancho chilies.
Anchos should not be confused with poblano peppers, or pasilla chilies. Poblanos are fresh, while anchos are dried (the two names get swapped sometimes in English-language recipes and resources). Pasilla chilies are dried chilaca peppers (a completely separate variety), but for some reason the word ‘pasilla’ is often incorrectly applied to poblanos and even ancho chilies.
Anchos are are available whole (as shown in the picture), and ground into either flakes or powder.
Scoville Heat Units
1,000-2,000* (fairly mild)
*Some poblano peppers (and consequently some ancho chilies) are considerably hotter than others, even when originating on the same plant. If in doubt, taste a small sample.