In recent years, the demand for green oils has been increasing, leaving behind the term liquid gold, which traditionally referred to virgin olive oil. This colour variation is only due to the oxidation state of chlorophyll, a molecule that forms part of plant respiration, through the assimilation of CO2 and the emission of O2.
In its normal state, chlorophyll is green, and when it is oxidised (by the action of light, oxygen (air) or water), it transforms into an orange-brownish colour (which is the well-known golden colour of virgin oil). And here, a reflection, the chlorophyll is in the skin of the olive, and also in the pulp, when it is still white, which means that “green oils” can be obtained with ripe/black olives, as long as their pulp is still white. And the same, even if you work with very green olives, and you obtain green oil, if you do not manage this oil very well, eliminating any oxidising agent (water, light and/or air), this green colour will turn yellow in a very short time (2 or 3 weeks). For this reason, the bottles destined for premium markets are opaque, or are packed in boxes.
Nutritional properties of green oil
Another thing that is associated with “green oil” is the nutritional and health-giving properties of a food rich in polyphenols (and pigments such as chlorophyll, or carotenes). Natural antioxidants, which in the mammalian organism, have been shown to act in the mechanisms of ageing (cellular oxidation), blood sugar regulation, cardiovascular and anti-inflammatory properties, which are beneficial to our health. Not forgetting the importance of oleic acid, the major component of virgin olive oil, and its properties for regulating the body’s cholesterol system, as well as nourishing the skin, mucous membranes, hair and digestive system.
To obtain oils rich in these molecules and to take advantage of their healthy properties for the body, it is necessary to know the characteristics of each variety of olive, to know when is the optimum time to harvest them, and how to proceed to the mill to obtain oils rich in these but at the same time, as long as it gives a powerful oil, rich in sensations, it is also necessary that it is not too aggressive (too bitter or spicy or astringent), which can penalise its commercialisation, however healthy it may be.
In the case of the Arbequina, the most common olive variety in Catalonia, in order to obtain oils with a good balance between sensations and antioxidant richness, it is necessary to work the olives very carefully during the harvest and the transport of the fruit to the mill, and to look for a stage of ripening of the fruit when the majority of the olives on the tree are already changing colour, no longer green, and varying between yellow and medium bright. At this point, for the arbequina variety, the maximum expression in aromatic sensations and richness in antioxidant concentrations is obtained. Then, in the mill, working under controlled process temperature conditions, around 25ºC, and adjusting the paste preparation time and water consumption (necessary to separate the oil from the rest of the olive components), to ensure that the antioxidant components, including chlorophyll, come out in the oil and not with the rest of the components of the olive paste.
The work of the producers, with their care in harvesting and transport to the mill, as well as all the actions applied to the olive tree throughout the year, are the first step, and very important for the production of a good extra virgin olive oil. Polyphenols are antioxidant agents, and their function is very simple: in the presence of an oxidising agent, they get in front and oxidise first, preventing the fatty acids from degrading. So if we are not very careful with the olives, in the whole process of harvesting, collection and transport, and the fruits are heated and begin to ferment, the proportion of antioxidants will decrease rapidly. Favouring the loss of green colour, spiciness, bitterness, astringency and the shelf life of this oil.
Once the oil has been produced, the work is not over. In order to guarantee complex oils, rich and powerful in sensations, it is necessary to do a very good job of managing the oils, in which it is necessary to stabilise them, eliminating all oxidising agents, as quickly as possible. This is why it is necessary to filter the oils within a few days, or to take meticulous care in the decantation of the oils, in suitable installations. To increase cleanliness and, above all, to store the oils in spaces that have neither light nor air chambers. These are the agents that can oxidise the oil, causing it to change colour from green to yellow, and reducing its natural antioxidant agents.
The elaboration and obtaining of the “green oil” is a work with several actors, that requires the implication and the good work of all, to be able to have healthy fruits, in the optimal moment of maturation and oil content, in the oil mill, and a treatment typical of a food artisan workshop, at the same time of a good knowledge of how to “take care” of the oil to be able to make arrive an excellent oil to the consumer, as are the oils of the Espluguenca, the Agrarian Cooperative of the Espluga Calva.
Esteva Martí Perelló
Grup d’olis de l’IRTA