Pimientos start their journey as a type of chili known as 'cherry peppers.' Small and red (hence the name),
Most folks use pimientos as a garnish, either in the center of a green olive or mixed with cheese.
Freshly picked green olives have a bitter taste, so they are traditionally cured in brine before being packed.
Even then, their flavor is more enjoyable with a little something extra, and in the U.S., that 'something' is most often the pimiento.
Until the early 1960s, pimientos were sliced and then stuffed into olives by hand. The Sadrym company from Seville, Spain
The more modern machines use a mix of crushed pimientos combined with a binding agent like gelatin or guar gum, which is formed into large sheets