In general, green olives are under ripe with firmer flesh and a lower oil content. Olives picked in a riper stage are a deeper green color. Olives that are tree-ripened turn dark brown or black, naturally. Green olives are soaked in a solution of lye, which removes a bitter-tasting substance called oleuropein. Then they're thoroughly washed to remove the lye and placed in a barrel of salt brine.
Black olives go straight into a brine solution, which promotes a lactic-acid fermentation.
Then they're treated with lye to remove the oleuropein. Some ripe olives are debittered with salt alone. I personally avoid California black olives, which are relatively tasteless imitations of the real thing. Actually, they are unripe green olives whose black color is obtained by exposure to air after lye extraction-a bland American version of a wonderful Old World edible. All Rights Reserved.