Bright green, they're often referred to as dolce (sweet), and come from Castelvetrano, Sicily, from the olive variety nocerella del belice. They have a Kermit-green hue, meaty, buttery flesh, and a mild flavor.
According to Professor Stan Kailis one of Australia’s foremost experts in processing table olives, the Green Sicilian olives found in Australian supermarkets are likely to be the Sicilian olive variety Nocellara de Belice that have been treated using the Castelvetrano style of pickling. The fruit is bright green as they have been treated with lye (caustic soda). If they were naturally fermented without lye they would be a grey/ green colour. Following is an excerpt from Stan’s book “Producing Table Olives” (Kailis and Harris 1997) – available from The Olive Centre
“Castelvetrano-style olives are popular in Sicily. They are different to the Sicilian-style green olives that undergo a natural fermentation without a pretreatment with Lye. With Castelvetrano table olives, a local variety, Nocellara de Belice, is used. After washing the raw green olives they are placed in a 2-3% lye solution in a suitable plastic barrel or drum. After one hour, coarse salt (3-4 kg/100L barrel) is added and agitated to mix and dissolve the salt. The barrel is sealed and further agitated to ensure mixing and to form the processing brine. The olives are ready to eat after two weeks. When the barrel is opened, the lye/salt brine is drained and the olives are washed to remove excess lye. Under ambient storage conditions the Castelvetrano olives have a shelf-life of only a few months, especially under hot conditions. As this olive style is a seasonal product, long-term storage is not required.
Nocellara de Belice olive trees are not available in Australia. The fruit, however, is similar in size and shape to the spanish variety