The thin white lines sometimes seen on the skin of a jalapeno pepper are an indicator of chile heat.
The thin white striations on jalapenos are known as “corking.” To find out if these lines indicate that a jalapeno is hotter than a smooth-skinned specimen, we gathered samples of each and tasted them several times both straight up and cooked in our Stir-Fried Thai-Style Beef with Chiles and Shallots. Our results were all over the map: In some instances, tasters thought that the corked chiles tasted hotter; in other tests, it was the smooth-skinned chiles that kicked things up a notch.
Danise Coon of the Chile Pepper Institute at New Mexico State University helped us get to the bottom of this. She explained that corking is merely a genetic trait with no bearing whatsoever on chile heat. The differences that we detected probably had to do with their cultivation, she said. Chiles grown in hot, arid environments like New Mexico undergo a lot of stress, and stressed chiles produce more capsaicin (the compound responsible for the sensation of heat) than those grown in more temperate places, like California.
Our advice: If you want more control over the heat level when you’re cooking with fresh chiles, start with an easy-to-measure heat source, such as cayenne pepper or red pepper flakes, then add small amounts of fresh chiles, removing the ribs and seeds—both primary sources of the chile’s heat—to temper the spiciness.