It seems like it is always hit and miss when it comes to eating jalepenos. What are some ways to tell if the jalapeno is hot or not, besides tasting it?
The only way to test for capsaicin besides tasting is chemical testing, namely liquid chromatography. Problem is, the same kind of chili can be quite different in heat, even on the same bush it can be quite different from my experience. No idea why, though.
Here is one tip on how to check the heat of a chili without actually eating part of it, but still cutting it apart: Cut through the chili below the stem, touch the membranes, touch your tongues, feel the heat. http://www.chow.com/videos/show/chow-tips/78517/how-to-test-the-heat-of-your-chiles
You can adjust the amount of heat a chili adds to the dish by removing the white membranes. Just add the colored flesh, check for heat, and add membranes until the desired spiciness is obtained. Capsaicin is only produced in the white mebranes in the center. It may move inside the fruit, though. Areas closer to the membranes will be hotter (like, the seeds), than other parts.
Look for the white strecth marks it indicates the jalapeño is old and has endured more stress, it appears that being older and endure dry times increases something in their inner oil that makes them more spicy, of course there's no scientific evidence for this and each jalapeño vary its level of hotness but on average I have picked them like this and they never fail to turn me red
btw the color has nothing to do
source: trust me I live in mexico
If it's a great big shiny Jalapeno, chances are it's a Texas A&M mild Jalapeno (TAM). Very popular with farmers because yield is good, and fruit is pretty. Stores lik3e it for same reasons. Organoleptically speaking, you may as well get a bell pepper. They're not hot. Usually best to kick it up a notch with something like Serranos, they're about as hot as old style jalapenos. Hot jalapenos will be smaller than TAMS, and have some brownish stripes that many people who don't know their peppers find offensive.