Serrano chilis are small to medium size chili peppers with good heat and a sharp flavor. They look like a slender jalapeño pepper. As it ripens, it turns from green to red to yellow, and some of them will turn a chocolate brown color. Serrano peppers are often used in salsas, marinades, sauces and chilis. Its size and shape make the serrano difficult to core and seed, so the best way to temper it is by using less of it.