
Red chili pepper is the pungent, ripened fruit of Capsicum plants in the nightshade family, whose heat comes from capsaicin.
Sharp capsaicin heat that builds on the palate, over a mild vegetal, faintly fruity flesh; the pith carries the strongest burn.
Slice, muddle, or sliver it into the build to add capsaicin heat, dosing by variety and by how much pith and placenta are kept or removed to dial the burn up or down; since capsaicin is hydrophobic, water does not wash the heat away.
Only another capsaicin-bearing chili can supply the defining heat — dried chili flakes, a chili tincture, or hot sauce work as an accent; unrelated pungent ingredients such as black pepper or ginger give a different sensation and cannot stand in.
Sweet/bell pepper
Sweet or bell peppers are also Capsicum fruit, largely C. annuum, but are non-pungent, contributing vegetal flavour and colour without capsaicin heat; a red chili pepper is defined by its pungency.
Black pepper is the dried fruit of Piper nigrum, an unrelated family; its pungency comes from piperine rather than capsaicin, and it shares only the English name 'pepper'.
Growers cultivate chili peppers on domesticated species of the genus Capsicum, of which Capsicum annuum is the most widely grown. The heat is capsaicin and related capsaicinoids, concentrated in the placental tissue and internal white pith that hold the seeds rather than in the seeds themselves; pungency ranges from effectively none to extremely hot depending on variety and growing conditions.
Fresh chilies are perishable; refrigerate and use within a week or two, discarding any that soften or spoil.
Capsicum was domesticated in the Americas at least as early as roughly 3000 BC, with Capsicum annuum domesticated in Mexico.