Mexican Peppers
Chiles, Chilis, Chillis in Mexican Cuisine

If corn is the edifice upon which Mexican cooking is built, its soul lies in its seemingly infinite number of peppers. Sweet or spicy, they are as brilliant as glistening jewels when fresh, but turn darkly mysterious, hinting at complexity and nuance when dried.  When we talk of hot peppers we variously use the names chilis, chillis, or chiles. The Nahuatl called them chillis, but the Spanish word is chile(s). As Spanish is the language of Mexico, we shall call them chiles with all apologies to any dissenters.
Chiles have been present in the Mexican diet since 7500 B.C.  The Mayans tossed them in the water used to boil beans, and mixed them into their cacao.  They made sauces (salsas), the first being a simple sauce for dipping tortillas. 
The great sauces called moles, arguably the crown of Mexican cooking, blend several types of chiles, fresh and dried, each for its own flavor and property.A miracle of taste and nutrition, chiles are not juicy like tomatoes, not fleshy like peaches, they are essentially hollow containers for those burning seeds.  Chiles also function as a thickener.  The pre-Hispanic peoples did not have wheat, and their corn dough (masa) was not used to thicken.  Chiles, especially in their dried form, allowed them to thicken sauces without flour. 
Though the Mayans sometimes grew chiles in plots by themselves, they were mostly grown in the fields with tomatoes.  This may have been an early form of companion planting, as the capsaicin in chiles repels mammals by the very burn they produce when eaten, and may have driven away field invaders.  They do not bother birds which would fly into the tomato patches to feast on peppers and perhaps snack on a tomato worm as well.  Once the birds had eaten, they flew off, spreading the seeds throughout Central and South America.  The mammal of the human variety had to learn how to deal with the burning seeds.
Chiles are a rich source of vitamins and complemented the other native foods in the Mexican diet.  Their heat is measured in Scoville units. Once fresh chiles begin to wrinkle, they lose flavor.  They should be eaten as quickly as possible. To store them, wrap them in paper towels and put them in a paper bag in the refrigerator.  Plastic creates a humidity that speeds deterioration.
In Mexico many varieties of chiles are used to create a dish.  Just as we all like to combine many fruits for their flavors, so chiles are combines for their special qualities - the smoky taste of chipotles with the hot, but fruity taste of habaneros.
Frequently chiles will be roasted.  This removes tough skin.  The large ones are roasted as you would roast a red bell pepper.  It is your choice to do this over direct flame or under the broiler, but please don't put them in a plastic bag afterward.  A paper bag is fine or just put them in a bowl and cover with a dish or towel.  Small chiles are best roasted directly in a small heavy-bottomed pan (cast iron is gret!) or on a grill.  These are rarely peeled.

How to work with dried chiles
(Special thanks to Miguel Ravago of Fonda San Migue~ Austin, Tx )

The heat of chiles lies in the membrane of tissue within the shell itself. The seeds absorb some of this heat.  You can control the heat to the extent that you remove the membrane and by removing or leaving the seeds.
In his book, Fonda San Miguel, chef Miguel Ravago tells us the best way to handle dried chiles. He advised us that to seed dried chiles, "Use a sharp paring knife to make a slit down the side and carefully scrape out the seeds. To Fry, heat oil to shimmering, fry for 10 to 15 seconds, turning once. Do not burn. Drain on paper towels."
To toast, place on a hot comal or dry skillet for 10 to 15 seconds, turning once or twice. Do not burn." You can rehydrate chiles," Miguel continues, "by soaking them in very hot water for 15 to 20 minutes."   click for Fonda San Miguel
Always remember that chiles should be handled carefully: wear rubber gloves and do not rub your eyes or lips.
Fresh Peppers
Bell Pepper  - The bell pepper is the most commonly grown pepper in the US.  Mexico has a large export business with bells, but doesn't use them as much in their own cooking. We include it here only due to its familiarity.
Cayenne - This is long, thin pointed chile, on average 3 inches long.  It is not a Mexican native.  Though a native of South America, it has endeared itself around the world. It is fire itself.

Chilaca - A fresh form of the pasilla.

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Chiltepin, pequin and Tepin - These are small, wild chiles, very attractive to birds.  The word chiltepin may had derived from the Nahuatl combination of chilli and tecpintl which translates to 'flea chile' referring both to its size and its bite. In Puebla, the piquin is called pichichi.  There are many varieties growing wild in Mexico and southwestern states in the US.  They do well in home gardens. Legend has it that Texans eat them off the bush and use them instead of soap to wash their children's mouth if they use a bad word.

Güero - Servered on the side with Hot Dog Purchase in Los Algodones
This is a waxy yellow or yellow-green chile.  It is similar in appearance to the jalapeno, but is larger and Milder.

Habanero - Watch out for habanero which measures scorchingly high in Scoville units, many times hotter than Jalapeno. This is the hottest pepper of all.  It is well to adjust the heat by eliminating seeds to taste the unique flavor of this chile, described frequently as 'fruity, sweet, aromatic.   KEEP AWAY FROM YOUR EYES when working with habaneros.

Jalapeno - The best known of the chiles and readily available in market, the crisp jalapeno is complex in flavor.  It measures 2,500 - 10,000 Scoville units while the habanero measures between 80,00 to 150,000.   It is named after the city, Jalapa in Veracruz.

Poblano - A largish chile, 4 to 4 inches long in general.  It is dark green with a deep, mellow flavor.  This is the most popular chile for stuffing .  It is generally roasted and peeled before use.   This is a mere 1,000 -1,500 Scoville units.

Serrano - The serrano is the smallest of the fresh chiles, slim, narrow and firm. It can be a substitute for jalapenos, though it is harder to deseed.  It is medium green in flavor.  It is available canned in vinegar.  It measures 10,000 to 25,00 Scoville units.  This is fire.  Serrano means 'from the mountains' and was first grown in the mountainous regions of northern Puebla and Hidalgo.  they are often pickled en escabeche.

Dried Mexican Peppers

Fresh peppers often change their name when dried.  They also change their flavor, as the flavors concentrate in the drying process.  Once dried, their interaction with other foods is increased.

Ancho- This is a ripened poblano chile that has been dried.  It is dark brown with a red hue. The name translates as 'broad' for the width of its pods. They may be stored in air-tight containers or ground into powder.  They are part of the great mole sauce.

Cascabel - The name means rattle (and is the name for rattlesnake in Mexico).  It is grown primarily in Jalisco and Guerrero.
Chipotle - Chipotles are dried jalapenos. The name is derived from the Nahuantl combination of chil and potle meaning simply smoked chile.  They originated in  Teotihuacan, present-day Mexico City, where they were easily found in the markets. They are so readily available that they have become trendy. They are smoke-dried, and often found packed in adobo.

Guajillo - This chile is common in northern and central Mexico.  It is long, thin and smooth.  They vary in heat from modestly hot to blazing.  They are used primarily in sauces, in complement with other chiles.

Mulato - This is similar to ancho in that it is a dried poblano, though not one that has been ripened.  It is darker than the ancho. When in desperation, the ancho my be substituted, but it is readily available.

Pasilla - This is the dried chile chilaca.  It is hotter than the ancho. It is used primarily in the dried pod or powdered version.   It harmonizes well with other chiles.