Growing Hot Peppers: Can You Make Them Hotter?

Peppers (Capsicum spp.) are a common, popular, and easy-to-grow vegetable in the home garden. There are 26 wild species and 5 domesticated species of peppers, with hundreds of cultivars. Peppers are now grown in almost every country in the world.

Peppers are a warm-season crop that will languish in cool weather. They prefer well-drained soil of moderate fertility and are not picky about soil pH, but they must be grown in full sun.

Peppers are quite versatile in the kitchen. They can be eaten raw or cooked. Sweet bell peppers provide flavor to salads, omelets, soups, and casseroles. They can also be stuffed and baked. Chili peppers are hot (spicy, pungent) and can be used in a variety of ways in the kitchen. They add spice and flavor to salsas, pickles, and chilis and are a staple of many ethnic cuisines, including Mexican, Thai, Indian, and Chinese.

Chili peppers can range from somewhat mild to those that burn your mouth. Commercially, they are grouped into "mild," "medium," "hot," "extra hot," and "extremely hot."  The heat of a particular chili pepper variety, such as 'Jalapeno', 'Cayenne', 'Hungarian Hot Wax', 'Serrano', 'Poblano', etc., is always defined as a range. Genetics and the environment influence heat. Ripeness plays a role: a pepper gets hotter closer to being fully ripe. Peppers from the same plant can also significantly vary in heat from each other.

The class of compounds causing pungency in plants, such as chili peppers, is called capsaicinoids. There are 22 different compounds, but the major capsaicinoid in chili peppers is capsaicin. Capsaicin is most prevalent in the white membrane surrounding the seeds.  It is a chemical irritant and can irritate eyes, mucous membranes, and skin. Be careful and wear gloves when handling hot peppers. Don’t touch your nose or eyes. Wash your hands really well following contact.

In 1912, a chemist at a pharmaceutical company in Detroit, Wilbur Scoville developed the Scoville organoleptic test that scientists use to define a chili pepper's heat. This is also known as the Scoville scale or rating. Peppers are determined through testing to have a range of Scoville heat units (SHUs). Essentially, a hot pepper extract is diluted and tasted by a panel of trained testers to see if it still has "heat." The extract continues to be diluted and tested until no heat is noticed by the panel. That process, the number of dilutions, determines its Scoville rating. Each individual variety of pepper has its own range on the scale. Note that this is a rather subjective testing scenario.

More recent scientific tests have defined pepper heat levels. High-performance liquid chromatography (HPLC) was developed in the 1980s. In this test, the pepper’s heat is assessed quantitatively by measuring the concentration of capsaicinoids, especially capsaicin content. This is objectively a more accurate test. Yet, the Scoville ratings are still used to indicate the chili pepper’s heat.

The pepper plant is thought to create capsaicin as a protective response to keep foraging rodents from eating the fruit. A rodent's digestive system would create unviable seeds. Interestingly, birds have no reaction to capsaicin. They can eat the peppers and disperse viable seeds. Birds were responsible for the geographic movement of chili peppers until humans began to cultivate them.

When a chili pepper plant is stressed, the plant reacts by creating more capsaicin, within limits. A jalapeno cannot be made to be as hot as a habanero, but it can still be nudged into an upper heat range for a jalapeno. Research indicates that the most influential stressors are high temperatures and drought. Peppers grown in red soil also seem to have higher heat levels.  If you want hotter peppers, grow them in lean soil and water only when absolutely necessary. Some gardeners use dark mulch, even black or red plastic, to raise the ambient and soil temperature around the chili pepper plant. Conversely, grow your chili peppers in ideal conditions with moderately rich soil and even watering for predictable heat results.