A Complete Guide to Table Olive Varieties and Curing Methods

Why Raw Olives Are Inedible

A ripe olive straight off the branch is nearly impossible to eat: it carries a sharp, mouth-puckering bitterness. The compound responsible is oleuropein, a phenolic that can make up as much as 14% of a young olive's dry weight. Under the International Olive Council's trade standard, a fruit only earns the name "table olive" once that bitterness has been removed and the olive preserved, either through natural fermentation or heat treatment.

Five Ways to Cure a Bitter Fruit

Producers reach the same goal — stripping or breaking down oleuropein — through different routes. Natural, Spanish- or Sicilian-style curing submerges olives directly in brine, where lactic acid bacteria ferment the fruit over weeks. Dry-salting buries olives in layers of salt until they shrivel and concentrate. Cracking or splitting the flesh without breaking the pit speeds up brine penetration on firm, green fruit. Water-curing skips salt and acid altogether, soaking olives in daily-changed water for ten to fourteen days.

Lye, or sodium hydroxide, treatment works fastest of all, cutting bitterness within hours before the olives are rinsed and brined — the same underlying chemistry behind California-style black olives, where green fruit is darkened through oxidation in an alkaline bath rather than left to ripen on the tree.

Green, Turning, and Black: One Fruit, Three Harvest Windows

Colour categories aren't separate cultivars — they describe harvest timing. Green olives are picked early in the ripening period, before any colour change. Olives "turning colour" are picked mid-ripening, ranging from pink to wine-red. Black olives are picked at or near full ripeness. Under the IOC standard, both the harvest colour and the curing method must appear on the label, so a jar's name tells you exactly when the fruit was picked and how it was processed.

What the Calibre Numbers on the Jar Mean

Numbers like "160/180" printed on an olive jar aren't marketing — they're a size grade defined by the IOC standard: the range of how many olives make up one kilogram. A lower number means larger fruit; a higher one means smaller. The standard also caps how much size can vary within one grade, no more than 4mm between the largest and smallest olive in a 100-piece sample. Calibre labeling is mandatory only for whole, pitted, and stuffed olives; sliced or chopped styles are exempt.

Quality Grades: Extra, First, and Second

The IOC standard sorts table olives into three commercial grades. "Extra" or "Fancy" covers olives with the fullest expression of their variety's traits and only the slightest defects; whole, split, pitted, or stuffed olives need to exceed calibre 351/380 to qualify. "First" or "Select" covers good-quality olives with minor defects and is open to every style except chopped and paste olives. "Second" or "Standard" covers olives that don't meet the higher grades but still satisfy the standard's general requirements — the category with the widest defect tolerance.

Stuffed Olives and Olive Paste

Stuffed olives are pitted fruit filled with pimiento, almond, anchovy, capers, or citrus peel, among other fillings the standard recognizes; olives with a partly or fully empty cavity are graded as a defect. Olive paste, by contrast, is defined narrowly: crushed olive flesh and nothing else. Chopped and sliced styles carry their own tolerance rule — no more than one pit fragment per 300 grams of drained flesh.

Reading the Brine: Storage and Spoilage Signs

A cloudy brine isn't automatically a red flag: the IOC standard notes that fermenting olives can carry billions of lactic acid bacteria and yeast per millilitre of brine as a normal part of the process. What does signal spoilage is an off smell, an unusually soft texture, or a colour that departs clearly from the fruit's expected shade. Heat-sterilized styles, like oxidation-darkened black olives, must be processed long and hot enough to destroy Clostridium botulinum spores, and any olive should be kept submerged in its brine and refrigerated once the jar is opened.