The jalapeño is a medium-sized chili pepper pod type cultivar of the species Capsicum annuum. A mature jalapeño chili is 5–10 cm long and hangs down with a round, firm, smooth flesh of 25–38 mm wide. It can have a range of pungency, with Scoville heat units of 3,500 to 8,000.
Compared to other chilies, the jalapeño heat level varies from mild to hot depending on cultivation and preparation and can have from a few thousand to over 10,000 Scoville heat units. The number of scars on the pepper, which appear as small brown lines, called ‘corking’, has a positive correlation with heat level, as growing conditions that increase heat level also cause the pepper to form scars. For US consumer markets, ‘corking’ is considered unattractive; however, in other markets, it is a favored trait, particularly in pickled or oil preserved jalapeños.