People often think that table olives can come straight off the tree and into a jar with perhaps some seasoning, but this is not the case and far from it. The olive fruit is a drupe. It has a bitter component which is called ‘oleuropein’, a low sugar content from 2.6-6% when compared with other drupes which have on average 12% or more and finally a high oil content from 12-30% depending on the time of year and variety.
Due to these characteristics it makes it a fruit that cannot be consumed directly from the tree and it has to undergo a series of processes that differ considerably from region to region, and which also depend on the variety of olive. Some olives are, however, an exception to this rule because as they ripen they sweeten right on the tree, in most cases this is due to fermentation. One case is the Thrubolea variety in Greece, however this is not common.
Oleuropein, which is distinctive to the olive, has to be removed as it has a really strong bitter taste and those who have eaten an olive straight off the tree know what I am talking about: it is not, however, pernicious to health. It just tastes terrible. Depending on local methods and customs, the fruit is generally treated in sodium or potassium hydroxide, brine or successively rinsed in aerated water.
The olive's suitability for table consumption is a function of its size, which is important to presentation. Olives between 3 and 5g are considered medium-sized, while those weighing over 5 g are large. The stone should come away easily from the flesh and a ‘flesh:stone’ ratio of 5 to 1 is acceptable; the higher this ratio the better the commercial value of the olives. The skin of the fruit should be fine, yet elastic and resistant to blows and to the action of alkalis and brine.
High sugar content in the flesh is an asset. The lowest acceptable level is 4%, especially in olives that undergo fermentation.
For table olives oil content should be as low as possible because in many cases it impairs the keeping properties and consistency of the processed fruit. Only in certain types of black olives is a medium to high oil content desirable.
In Spain most of the table olives are green olives. These are obtained from olives harvested during the ripening cycle when they have reached normal size, but prior to colour change. They are usually hand picked when there is a slight change in hue from leaf-green to a slightly yellowish green and when the flesh begins to change consistency but before it turns soft. Colour change should not have begun. Trials have been run to machine harvest table olives, but owing to the high percentage of bruised fruit they had to be immersed in a diluted alkaline solution while still in the orchard, this being said table olive are still in their majority harvested by hand. Recently harvested, the olives should be taken to the plant for processing on the same day.
Green olives are processed in two principal ways: with fermentation, which is considered the Spanish style, and without fermentation, which is considered the Picholine or American style.
In Spain the majority of olives are treated in a diluted lye solution (sodium hydroxide) to eliminate and transform the oleuropein and sugars, to form organic acids that aid in subsequent fermentation, and to increase the permeability of the fruit. The lye concentrations vary from 2% to 3.5%, depending on the ripeness of the olives, the temperature, the variety and the quality of the water. The treatment is performed in containers of varying sizes in which the solution completely covers the fruit. The olives remain in this solution until the lye has penetrated two thirds of the way through the flesh. The lye is then replaced by water, which removes any remaining residue and the process is repeated. Lengthy washing properly eliminates soda particles but also washes away soluble sugars, which are necessary for subsequent fermentation.
Fermentation is carried out in suitable containers in which the olives are covered with brine. Traditionally, this was done in wooden casks. More recently, larger containers have come into use that are inert on the inside. The brine causes the release of the fruit cell juices, forming a culture medium suitable for fermentation. Brine concentrations are 9-10% to begin with, but rapidly drop to 5% owing to the olive's higher content of interchangeable water.
When properly fermented, olives keep for a long time. If they are in casks, the brine level must be topped up. At the time of shipment, the olives have to be classified for the first or second time as the case may be. The original brine is replaced and the olives are packed in barrels and tin or glass containers. Sometimes they are stoned (pitted) or stuffed with anchovies, pimento, etc.
The most commonly used varieties in Spain are Manzanillo and Gordal.