Here is the Serrano Pepper, Capsicum annuum, scoville units: 10,000 - 23,000 shu. The Serrano Pepper is a chili pepper that originates from Puebla Mexico. In fact Serranias in Spanish means foothills. The flavor is bright and very unique in flavor. Serrano Peppers are 2 to 3 inches long and a 1/2 inch in diameter. With a Crisp and fresh flavor, it is the hottest pepper commonly available in supermarkets. Unripe peppers are green and turn to red, brown, orange and yellow as they ripen. Serranos are smaller and hotter than a Jalapeno. Open pollinated, 90 days.