There is a pepper grown in Japan called the Shishito peppers. Only 1 out of 10 is spicy and there’s no way of knowing beforehand
The pepper is small and finger-ling sized, slender, and thin-walled.
Although it turns from green to red upon ripening, it is usually
harvested while green. The name refers to the fact that the tip of the
chili pepper looks like the head of a lion , and in Japanese it is often abbreviated as shishitō.
About one out of every ten peppers is spicy. The occurrence of pungent fruit is induced by such factors as illumination, and other stress may predispose the peppers to turn spicy.
There does not seem to be any hard and fast rule to differentiate the
hot from mild without breaking it open. Producers often dodge the
question ; the prefectural agricultural testing center at Kishigawa, Wakayama in 2005 stated that the capsaicin
forms more easily in hot and dry conditions in the summer, and even an
expert has a difficult time differentiating the hot from the mild
growing on the same plant.
Therefore, some of the rules bandied about in blog-space etc., may be suspect or only semi-reliable. One supposed rule is that it is spicy if it has fewer seeds, and this can be determined by touch. Some say to try to sniff the pungency. Another says if the tip terminates narrowly then it is hot.
For cooking, a hole is poked in the pepper beforehand to keep expanding hot air from bursting the pepper. It may be skewered then broiled (grilled), or pan-fried in oil, or stewed in a soy sauce- and dashi-based liquid. It is thin-skinned and will blister and char easily compared with thicker skinned varieties”