The spicy or hot substance in chili is called Capsaicin and is an alkaloid. Many people claim that chili heat changes when it is heated. Some say it increases, some say it decreases. Let`s begin with the assumption that the chili heat increases. Technically, this is impossible, but the cause for this assumption can be easily explained. If you use chili powder, flakes, or whole chilies during cooking, the capsaicin is still bound. If you swallow down a whole chili pepper, then you won`t notice any burning in your mouth and throat area.
The burning will begin in your stomach when the gastric juices break down the chili. The Capsaicin must therefore be released to have an effect. Through cooking with chilies, more capsaicin is released into the dish, and the subjective perception of spiciness is stronger.
The question as to whether cooking decreases the spiciness can be answered with a clear NO. The alkaloid capsaicin is extremely thermostable. Its boiling point is between 210-220 °C and is not reached during cooking.
However, there are two possibilities that could decrease the chili heat through cooking or heating. Capsaicin is steam-volatile and can therefore enter the air during the cooking process. The other possibility involves direct grilling over coals, whereby temperatures of up to 400 °C can be achieved.