Olives are prepared in a variety of ways, called curing, to achieve their unique flavors and textures.
Ripe Olive Process
Black Ripe and Green Ripe olives are cured with small amounts of lye to bring out their naturally mild flavor. The process begins with hand-picked, unripened green olives that are cured in a series of lye and oxygenated water baths for multiple days or until the solution penetrates to the pits and removes the bitterness. A final rinse follows and, in the case of Black Ripe olives, iron is added as a color stabilizer. Carbon dioxide is introduced to neutralize the lye, after which the olives are sized, pitted, canned, and topped with brine. Once sealed, they're cooked with steam. Most similar to home-cured olives, the Green Ripe style is both cured and packed without the introduction of oxygen or iron.
Spanish Olive Process
Spanish olives also start as hand-picked, unripened green olives. They are first submerged in a bath of lye for a few hours to remove their bitterness. The fruit is then rinsed and soaked in a strong salt brine for three months, causing fermentation. This gives them their characteristic tartness. The olives are then bottled in salt brine, capped and pasteurized.
Sicilian and Kalamata Olive Processes
Sicilian and Kalamata olives have similar curing methods. Sicilian olives are soaked in salt and lactic acid for one year. The same process, minus the lactic acid is used to cure Kalamata olives, as well as Amphissa, Niçoise, Picholine, Cerignola and Gaeta olives. Similarly, many "home cured" olives are prepared by soaking the olives in water that is changed on a daily basis, after which the olives are cured in salt brine for several months.
Dry or Salt Curing
Dry Curing is the approach that starts with ripe, soft olives and results in salty, chewy varieties, such as the Dry Greek olive. Before curing, the olives are gently "smashed" to allow moisture to permeate their skins. Then the fruit is layered and covered with salt for four weeks. After curing, the olives are immersed in hot water to remove the salt, rinsed in cold water, and spread out to dry. The olives are then coated with olive oil (which is why they are sometimes called "oil cured")