Scoville units – measure of the hotness of a chilli pepper. Higher means hotter.
Chile de arbol: 25, 000.
Chili peppers should be well shaped, firm, and glossy. Their skin should be taut and unwrinkled, and their stems fresh and green. Avoid soft or sunken areas, slashes or black spots. Except for jalapenos, avoid cracks.
Wrap in paper towels and refrigerate up to three weeks. Do not store them in a plastic bag.