Olives (Olea europaea L.) and olive oil are regarded as one of the healthiest foods in the world. They have been used for at least a few thousand years, being mentioned in the bible too. This article looks at the fermentation through brining of olives which are also often called table olives. A similar article can be found on the production of olive oil which is regarded as an equally important food. The amount of oil is between 12 and 30% depending on the cultivar.
Olives are mainly fermented through lye treatment then brining. This is a well established process conducted primarily throughout the Mediterranean region but especially Italy, Greece, Morocco, Spain and Morocco. According to the Olive Oil Council, five countries, including Spain, Turkey, Algeria, Egypt and Greece produce over 70% of the world’s olives. which is about 2.65 billion kg (2015-2016 data). Olives are also treated similarly in the USA but the conditions are slightly different.
The main purpose of lye treatment is the removal of glycosidic proteins which produce an acute bitterness. This key bitterness protein is oleuropein. The other polyphenols are hydroxytyrosol (β(3-4-dihydroxyphenyl)ethanol), tyrosol (β(4-hydroxyphenyl) ethanol) and verbascoside; the major polycyclic triterpenes are the oleanolic and maslinic acids. The lye treatment hydrolyses oleuropein into β(3-4-dihydroxyphenyl) ethanol, oleoside 11-methylester and oleoside. These particular glucosides alongside oleuropein itself, in acidic medium, produce glucose and a number of compounds called, collectively, oleuropein aglycones (Bianchi, 2003).
The process of brining is not complex. The processing is often described as similar to sauerkraut except the olives are soaked in this lye before brining.
Olives for the table are first harvested when yellow and green. Some through are picked when they are dark red. They are treated with a 1.3-3.5% lye (sodium hydroxide). The higher level is extreme and most lye solutions will be between 1.6 and 2.0%. Olives are routinely batch treated in large containers. The olives are held at ambient temperatures between 22 and 26C.
It is a natural fermentation process too because no starter cultures are used as in other types of fermentation. There is however, a fraction of brining liquor used like a pitching culture as in beer brewing that is added to the brining mixture.
The fermenting organisms are Lactobacilli. The most common are L. plantarum and L. pentosus. Both these are commonly found in fermentation of pickled cucumbers and sauerkraut.
The lye treatment usually destroys a large proportion of the fermenting organisms as does subsequent washing but there are still enough microorganisms for further fermentation.
Thee is enough carbohydrate in an olive besides oil to support fermentation. The amount of fermentable carbohydrate is from 2 to 5% and is generally glucose.
References
Bianchi, G. (2003). Lipids and phenols in table olives. European Journal of Lipid Science and Technology, 105(5), pp. 229-242.
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