Olive Yield: What It Is and What It Depends On
Every year at the start of the oil season, the figure that is awaited with some trepidation is what the oil yield will be. It is a kind of productivity index, a percentage value that basically quantifies how many liters of oil were produced with 100 kg of olives.
It is a value that can vary significantly based on various aspects related to the entire Olive supply chain.
The oil yield of the crush, or the liters of oil obtained from the pressing of a certain quantity of olives, is the main topic during waits at the mill. In this value, expressed in percentage, the expectations and hopes of olive growers are catalyzed. A good yield can pay back for a year’s work and costs incurred as well as that of pressing. Generally, the oil yield increases over time and the latest crushings are more satisfactory.
Olive yield: what it’s all about
In the following article we will look at some aspects that are essential to better understand what we mean when we talk about olive yield and what variables condition this figure.
The aspects we will focus on are:
- What is meant by “surrender”
- What the yield of olives depends on
- The right conditions to foster yield
- The price and yield
What is meant by “olive yield”
The yield is related to the oil extracted during processing at the mill, is therefore the oil present in the individual fruits and depends mainly on the variety of olives, the weather (how much and when it rained) and the peculiar characteristics of the mill where processing takes place. In other words, if on productivity man can try to intervene in several stages, for yield, the only moment dependent and controlled by man is the pressing.
In fact, the yield is closely linked to the quality of the oil, the type of crusher, cold extraction and then with always controlled temperatures; reduced kneading times, generally favor, on the one hand, the quality and positive characteristics of the oil while on the other hand decreasing the yield and therefore the final quantity of oil obtained.
Want to know more about oil extraction methods?
Read the article devoted to this topic: What are the methods of olive oil extraction?
What the yield of olives depends on
The olive tree is a centuries-old plant that lives in strong symbiosis with the environment, of which it acquires a “genetic code” referring to the specific characteristics of the geographical area in which it is located.
As even imperceptible microclimates vary, therefore, so do the properties of the oil produced, with shades of remarkable quality from one harvest to the next.
For this reason, pedo-climatic conditions are so determinant in attributing value to an extra virgin oil: temperature, rainfall, altitude, soil type, exposure to sun and wind are all elements, in fact, that peculiarly affect the product, with the result of a remarkable diversity of organoleptic and qualitative characteristics.
The help of a favorable climate in regions that are by nature suited to olive growing-along with the use of scrupulous and rational agronomic techniques-are therefore ideal prerequisites for achieving a good quality extra virgin worthy of the name.
The variety (cultivar) of the olive plant, and thus the characteristics of the fruit (shape, size, pulp-to-stone ratio), greatly affects the organoleptic qualities of the oil.
There are more than 700 types of cultivars in Italy. The optimal choice of when to harvest also depends greatly on the number of plants, how loaded they are, and the means and resources available.
Broadly speaking, oil production and revenues from sale appear to be little affected by the harvest period. Therefore, postponing the harvest trusting in a better yield leads to only apparent (illusory) benefits.
In addition, the harvest is still subject to risk because any bad weather may preclude the possibility of harvesting, may damage or reduce the crop, etc. In other words, with time the probability of something going wrong increases.
The right conditions to foster yield
The time and manner used to harvest the olives equally greatly affect the final product.
In fact, there is no identical harvest period for all olives: it varies-over a season between September (for early varieties) and December/January (for late varieties)- depending on cultivar, environmental conditions and agronomic practices.
The veraison stage -that is, the progressive color change of the olive epicarp (i.e., the outer part of the fruit) from green to purple to black, depending on the variety- is the optimal one for obtaining a quality oil, rich in polyphenols and fruity.
A color variation -indicative of the increase in accumulation of oil, volatile components and antioxidant substances in the pulp- decisive, therefore, for the time of harvesting: harvesting which must not, however, take place before veraison, in order to avoid too modest a yield and excessive and unpleasant notes of bitterness and spiciness in the oil.
The methods for harvesting olives have also been handed down, for the most part, as they were in the past: in fact, traditional manual techniques coexist today alongside more modern mechanized systems.
It is not bad to remember that from a certain point onwards the oil yield of olives increases only apparently; various studies indicate that the inoliation of the drupe (the stage of ripening of the fruit, the drupe precisely, in which the lipid quota increases i.e., the amount of oil) begins as early as August (average period for Italy) and ends in November, so that beyond this date the increase in yield is only apparent since, with the dehydration (decrease in the watery part of the fruit), the ratio of total weight to extracted oil varies significantly.
It is an obstacle to a good yield whether a very coarse sized kernel or a pulverized kernel; in practice, placing the paste between the fingers, the latter should feel fluid, while feeling the minute fractions of the kernel almost sting the fingertips. It is of fundamental importance the presence of these kernel fractions that in the “continuous” promote “beaching,” that is, the separation in centrifugation of the liquid part from the solid part, which through these small particles drains as, precisely, water does on the sand in the beach.
Hammer crushers certainly cause more emulsion of the oil particles, but they seem to be able to extract more color from the olives while mullers, which have no contraindications as a method of crushing except for the slowness of the operation, seem to be able, where the is deemed excessive, to mitigate the bitterness in the oil.
It is therefore advisable, with tests, to define the average times of gramation that allow to obtain oils well endowed with polyphenols and pleasant to the taste and the best possible yield, let it be clear that in fact it is a matter of defining the best compromise, not for nothing that gramation is the most oxidative operation in the whole extraction cycle, and therefore it is the greatest risk to quality.
The price and yield
The cost of pressing is about 15 euros per 100 kg of olives, but it can vary from mill to mill and from the region of Italy where it is done.
Generally for small quantities of oil for family use, there are no obligations of any kind. If the number of liters produced is more than 200 liters, however, packaging is mandatory. In this case, the mill will request the private individual’s fiscal data for the issuance of the packaging invoice and will have to send communication to the relevant bodies for control checks. Packaging at the mill is done in 5-liter cans.
Alfio Lo Conte
Tecnico ed esperto degli oli extravergini di oliva, iscritto nell’Elenco Nazionale sezione Campania.
Maestro di frantoio con diploma, conseguito presso International Extravirgin Agency.
Read more articles by: Alfio Lo Conte
Recent Comments