Most of the heat in a chile pepper -- whether jalapeño, serrano, habanero, or another -- comes from the white ribs and seeds. Removing both reduces the chile's heat and allows more of the pepper's flavor to come through.
First, cut the pepper in half lengthwise. If you want the halves to stay intact for larger slices or a large dice, just trim out the seeds and ribs, cut out the stem, and slice the pepper as thick or thin as you like.
Otherwise, it's easier to get the seeds and ribs out if you cut each half in half again.
To get the seeds and ribs out, hold each quarter by the end. With the knife parallel to the cutting board, slice across the ribs and seeds. When you get to the top of the pepper, turn the knife downward toward the cutting board and chop off the stem with the same motion. (Here, we used a Granton Santoku knife; you may prefer a smaller paring knife.)
Reference: Help! I ate a hot pepper! (Cookthink)
Reference: How to seed a chile pepper (Cookthink)
Reference:: Why are some jalapenos hotter than others? (Cookthink)
What should you do if you eat a pepper that sets your tongue on fire?
Do not drink beer. Water won’t help either. (In a Caribbean folktale, children drown in a river trying to cool their tongues after eating habanero stew. See Dave Dewitt and Nancy Gerlach's The Pepper Pantry for the full story.) Capsaicin, the chemical that makes a hot pepper hot, doesn’t dissolve in water, so even ice water won’t help remove the heat.
Your best bet? Get milk. Because capsaicin is fat-soluble, a compound in milk can actually pull the capsaicin off your tongue and relieve some of the burn. Another option: eat bread or rice to absorb the heat. Cucumber can also have a cooling effect.
If you are feeling brave (or masochistic), you could try eating another pepper. According Robert Berkley, the author of Peppers: A Cookbook, you can build up a resistance to capsaicin by eating more chile peppers. With Berkley’s approach, you get the added high of a capsaicin-triggered endorphin release. Before you know it, you might be addicted to the hot little things.
Reference: How to seed a chile pepper (Cookthink)
Reference:: Why are some jalapenos hotter than others? (Cookthink)
