These are obtained from olives that are picked when their colour is starting to change. They are harvested before full maturity, when the flesh is quite firm and oil formation has not concluded. The process of darkening the fruit by oxidation is typical of California. Olives suitable for processing as green olives are selected as they enter the factory, then placed in brine at concentrations between 2.5 and 10 percent in inverse relationship to fruit size, and they are protected from air.
The olives are placed in large concrete tanks in an initial solution of 2 percent lye until they are ready for subsequent preparation. When they are to be prepared for the market, they are placed in low-concentration lye and then washed in water into which compressed air is injected. Further treatments in dilute lye, each followed by aeration, facilitate penetration through to the stone. Next, the olives are washed to eliminate lye residue and to lower the pH to close to neutral. Solutions of 0.1 percent ferrous gluconate or lactate are often applied to enhance fruit darkening. After placement in brine for a few days, the olives are ready for canning. Heat processing in the form of temperature and pressure-controlled sterilisation is fundamental to ensure the product keeps properly.