There are olives that are harvested when the fruit is close to full ripeness, once it has attained the colour and oil content corresponding to each particular variety. The are many types of preparations depending on local tastes. Those in greatest commercial use are now outlined.
BLACK OLIVES IN BRINE
These are typical of the eastern Mediterranean countries; in Grecce they are from the Conservolea variety, which grades at around 200 fruits per kilogram, and in Turkey they are made with the Gemlik variety. The fruit is picked by hand when black ripe, but before the olives overripen or are shrivelled by frost. They have to be transported as quickly as possible to the processing plant where they are sorted, washed and immersed in 8-10 percent brine. Large-scale plants use big 10-20 tonne tanks while small-scale processors continue to use wooden vats. At the start of fermentation the tanks are tightly sealed because the olives must not be exposed to air. The brine stimulates the microbial activity for fermentation and reduces the bitterness of the oleuropein. It drops to a concentration of 6 percent, which makes it necessary to increase it to 8 percent and even 10 percent, while homogenising it by operating a pump to activate circulation.
When the bitterness has been sufficiently weakened - how long this takes can vary greatly - the fruit can be sold. The colour fades during the process, but is corrected by aerating the olives for two or three days, although sometimes they are treated with 0.1 percent ferrous gluconate or lactate to make them a deeper black. Lastly, the olives are selected and packed in barrels or internally varnished cans, which are filled with 8 percent fresh brine. They are popular on the market because of their slightly bitter taste and aroma.
They are also packed in vinegar (25 percent of brine volume) and may even be heat processed; a few grams of oil are then added to each can to form a surface layer. The Kalamata variety is prepared in this way; the elongated, medium-sized olives are slit to absorb the flavour of the marinade and then canned.
BLACK OLIVES IN DRY SALT
Also of Greek origin, these are prepared using overripe olives of the Megaritiki variety. They are vigorously washed and placed in baskets with alternating layers of dry salt
equivalent to 15 percent of the weight of the olives. The end product is not bitter, but salty, and it looks like a raisin; it is for local consumption.
Finally, a mention should also be given to the numerous styles of table olive preparations in the different olive-growing regions. Some examples are olives treated solely
with water to sweeten them prior to crushing or splitting, which facilitates washing. In many cases, the olives are eaten after being seasoned with herbs, pieces of orange,
lemon, garlic, paprika, oregano, etc. Until the turn of the twentieth century, the table olive market was local, but since then it has expanded to non-producing areas
where table olives have become popular. This is particularly true of the Spanish, Greek and California types.