There are two ways of classifying chile peppersby their heat and shape. In 1912, pharmacist Wilbur Scoville invented a test to measure the hotness of peppers by diluting the pepper until the heat was just perceptible on the tongue. The Scoville rating is measured in multiples of 100; he rated a bell pepper 0, while a Japanese chile came in at 20,000 on the Scoville scale.
Following are the 11 most common categories of chile peppers, classified by their fruit shape and their heat (in Scoville Units):
Asian/Thai: Small slender, thin-walled fruits; green ripening to red; no distinct pepper flavor; high to extreme heat (8,000 to <60,000 Scoville Units). Very attractive plants are heavy producers. Use red ripe, fresh, or dried, to add heat to curries, marinades, soups, and stir-fries.
Cayenne: Long, curved peppers with two cells and thin wrinkled skin; generally green but can be yellow or purple; medium to high heat (5,000 to <60,000 Scoville Units). Super Cayenne'(1990 AAS Winner) is especially vigorous. Harvest red ripe; use fresh or dried to add heat to marinades, pizza, stews, soups, stir-fries, and curries.
Chile/Anaheim/New Mexico/Paprika/Pasilla: Long and tapered, with fairly thin walls and two cells; ripen from green to red; mild to medium heat (1,000 to <8,000 Scoville Units). Many varieties, some of which grow well in short northern climates and at high altitudes. They have mild pepper flavors; best roasted and stuffed, or chopped and added to ethnic dishes; good for drying when red ripe. The Paprikas have deep rich flavors; allow to ripen fully, then dry and grind up. Add to stews and soups and use as a garnish.
Habañero: Small lantern shape; thin-walls; fruity taste and extreme heat (8,000 to <60,000 Scoville Units). Fruiting may be erratic in northern gardens. Use sparingly when fresh in fruit salsas, ceviche, jerk sauces, and Caribbean curries.
Hot Cherry: Tomato-shaped, thick-walled green peppers; ripen to red; medium heat (5,000 to <8,000 Scoville Units). They have a rich, sweet flavor; use for pickles or poach them and stuff with meat or cheese.
Hungarian Wax/Banana: Long and conical, tapering to a point; medium thick walls; ripen yellow to red; mild heat (1,000 to <5,000 Scoville Units). Adaptable to many climates. Use yellow or red ripe for pickles and chutney, or add them to salsas and fried dishes.
Jalapeño: Short and stubby with thick meaty walls; deep green; medium to high heat (5,000 to <60,000 Scoville Units). Numerous varieties include Jalapeños for short northern climates, selections with yellow and orange stages of ripeness, and others that are highly productive. Harvest Jalapeños green; use fresh in salsas, pickle, and grill and add to tacos or burritos. Smoke dry - either green or red ripe - to make chipotles.
Ornamental/hot edible: Upright, small, round or tapered, and thin walled; medium to high heat (5,000 to <60,000 Scoville Units). Bred in a variety of colors and with different shaped peppers: 'Black Pearl' (2006 AAS Winner with black fruit), and'Super Chili' (1988 AAS Winner; small red chiles borne in large numbers). Taste these peppers cautiously first, as some are bitter, some are exceptionally hot; pickle to add heat to salsas, marinades, and soups.
Poblano (called Ancho when dried): Flat and round, slightly tapered with a blunt end; thin walls with three cells; dark green; mild heat (1,000 to <5,000 Scoville Units). Harvest green for roasting and stuffing; dry when red ripe and grind up for basic salsas and moles.
Santa Fe Grande: Medium-sized, tapered and conical; medium thick walls; yellow-to-red; medium to high heat (5,000 to <60,000 Scoville Units). Use fresh when ripe; pickle or roast and add to quesadillas and tacos. A new Santa Fe Grande type is 2006 AAS Winner 'Mariachi', a mild chile pepper with outstanding flavor when yellow or red.
Serrano: Slim, slightly club-shaped with medium thick walls; green; rich flavor; medium to high heat (5,000 to <60,000 Scoville Units). Use fresh in the green stage or fry or grill and use as a garnish or add to salsas, tacos, guacamole, and other traditional Mexican dishes.