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Note: This article was AI-translated from Arabic and is currently under manual review. The author is not responsible for any translation errors. Please refer to the original Arabic text for the most accurate and authoritative information.
Olive Oil Quality from Tree to Table | Episode Two
How do good manufacturing practices protect the oil's flavour and quality during crushing, malaxation and separation?
Sound fruit harvested at the right time may arrive at the mill, only for an oil to come out that is less distinctive than its quality allows. The cause may be a setting that has not changed since last season, washing water that is no longer clean, or an actual temperature that bears no resemblance to the number shown on the control screen.
In the first episode we followed farm mistakes up to the delivery of the fruit. Here we follow its journey inside the mill, where good manufacturing practices determine how much oil we extract and how much fruitiness and natural compounds we preserve. Owning a modern line requires operation suited to each batch, and tests that reveal the effect of daily decisions.
Fruit differs in variety, ripeness, moisture, infestation and waiting time. Mixing it at reception or processing it without inspection costs the mill the chance to fine-tune the process and trace the causes of any defect. That is why the batch identity and its harvest and arrival times are recorded, its condition is assessed, and unsound fruit is separated from batches intended for premium quality. [1]
One detail worth checking is fruit left at the bottom and in the corners of the feed hopper; continually adding a new crop on top of fermenting residues can spoil the results of sound batches. The hopper should be checked for complete emptying, places where fruit gets trapped should be monitored, and the workflow organized to reduce waiting inside the facility. [2]
Having a washing unit does not guarantee clean fruit. Water loaded with mud, juice and fruit debris can transfer contamination, especially to damaged fruit. The water should be fit for the required food use, its cleanliness should be monitored and it should be renewed as needed according to the actual load, while checking how efficiently soil, stones and leaves are removed before crushing. [1, 3]
Saving water is not achieved by running a dirty washing tank for the whole shift, but by managing water consumption efficiently, monitoring and renewing it, and cleaning the tank on a schedule that matches the processing volume and the condition of the fruit, so that washing does not become a source of contamination.
Likewise, deliberately adding more leaves to give the oil a stronger green colour does not make up for fruit quality or sound processing; colour alone does not prove oil quality. Leaves may affect the oil's pigment and phenolic content, as well as its flavour, bitterness and astringency, to degrees that vary with variety, leaf proportion and extraction conditions.
From our practical experience, an excess of leaves may be accompanied by a noticeable change in flavour balance, with more bitterness or astringency, which an experienced taster can detect when comparing batches. But detecting this change is not enough on its own to determine its source; strong bitterness does not prove that leaves were added, and natural bitterness and pungency are positive attributes of virgin oil. Judgement should therefore rest on a controlled sensory evaluation, supported by processing data and appropriate analyses, not on colour or individual impression alone.
Crushing opens the fruit tissue and prepares the paste for extraction, but it also affects the oil's composition. Industrial trials have shown that the rotor speed of the crusher affects extraction efficiency and some phenolic compounds; so no single speed can be described as always the best. [4]
Keeping the screen, speed and feed rate at one setting for all batches is a potential mistake, especially when fruit moisture and ripeness change. Settings should be adjusted to the characteristics of the paste, its temperature and the condition of the working parts monitored, and the effect of any adjustment on both yield and flavour evaluated. [2, 4]
Malaxation helps oil droplets coalesce, but it is also a stage in which aroma compounds form and phenols change. Adjusting time or temperature may improve extraction without necessarily improving flavour and stability; and cutting them to the minimum may weaken separation efficiency. Process-optimization trials show an interaction between crushing settings and malaxation temperature and time. [5]
The mistake is to use a fixed time for all varieties, or to extend malaxation simply because the separator is not ready. The temperature of the paste itself must be measured with a verified instrument, not inferred from the heating-water temperature or the set point. And the "cold extraction" label is no substitute for checking the quality of the resulting oil. [1, 5]
Oxygen plays a role in enzymatic reactions that help form positive aromas, but it also takes part in oxidation pathways that can consume phenols. That is why it is wrong to generalize that more exposure of the paste to air is beneficial, or that reducing oxygen to the lowest level improves every characteristic of the oil. An industrial trial on the Picual variety showed that the effect of oxygen management differed depending on whether it was applied during crushing or malaxation. [6]
Sound management means operating the malaxer, its covers and its fill levels according to its design, minimizing uncontrolled opening and exposure, and evaluating any use of inert gas through actual measurements and results, taking into account the variety and the desired attributes. [6]
Adding water may make some pastes easier to process, but too much of it can increase the transfer of hydrophilic compounds, including some phenols, to the water phase. The right amount depends on the extraction system and the moisture of the paste; a recipe for a three-phase decanter should not be carried over to a two-phase one, and not every problem should be treated with more water or hotter water. [2]
In the vertical centrifuge (separator), poor adjustment can increase oxygen intake or the loss of some minor components during polishing. The goal is effective separation within the machine's operating conditions, monitoring water, temperature and feed rate, while measuring residual oil in the pomace and wastewater to estimate extraction efficiency. [2, 7]
The line may keep running smoothly while old paste remains at the end of a malaxer, in a joint, or in a part that is hard to clean. These residues can become a source of off-odours and fermentative changes that carry over to the next run. Special attention is needed after stoppages, when processing deteriorated fruit, and in old traditional press systems that use mats or discs. [1, 3]
Prevention requires a cleaning and maintenance programme suited to the design of the line and the workload, verifying the removal of residues and cleaning agents, and ensuring that materials in contact with the product are suitable. Shiny outer surfaces do not prove that the internal spots that trap paste are clean. [3]
No; mill hygiene is a system that covers the production line, aisles, handling equipment and surrounding yards. Fruit residues, paste, pomace and spilled oil and water must be removed as they occur, floors kept easy to clean and well drained, and cleaning methods that raise dust or scatter spray near the fruit, paste and exposed oil avoided. The aisle between two machines can become a route for contaminants, even if both machines are clean.
Forklifts and carts need cleaning and maintenance that prevent them from carrying soil and waste on their wheels, or leaking fuel, lubricants and hydraulic oil. Their movement between outside and inside should be organized, with dedicated equipment for clean areas where possible, and checked for cleanliness before entry. Electric forklifts can be used inside the mill to avoid combustion exhaust from fuel-powered forklifts, while still keeping wheels clean, maintaining them and preventing oil leaks. Protecting the production environment means controlling what handling equipment carries and emits, not just cleaning its path after it passes. [1, 3]
This extends to managing olive pomace, vegetation water and wastewater from extraction; they should not be left in open heaps or haphazard ponds around the plant. Their accumulation and poor containment can generate fermentative odours, attract pests and increase the chance of contaminants reaching work areas. These by-products should be collected in dedicated facilities that prevent leaks and overflow, kept separate from fruit and oil routes and air intakes, and their transport, use or treatment organized in line with applicable requirements. Protecting the oil begins with a clean, well-managed production environment, not only with the cleanliness of the surfaces it touches.
A higher number of kilograms extracted is not enough to judge a shift's success. I recommend a record for each batch that brings together the actual operating settings, waiting time, water consumption, yield, and the results of chemical testing and sensory evaluation of the oil as it comes out. A controlled comparison before and after changing the settings helps show what improved and what declined. [1, 2]
Fruitiness or phenol content may change even while some conventional indicators remain acceptable; so tasting the output and tracking its attributes deserves as much attention as monitoring extraction efficiency. The result of a single batch should not be used to judge the whole season's operation. [5, 6]
A mill succeeds when it turns sound fruit into an oil that keeps its distinction, with a suitable economic yield. This requires an operator who understands the effect of each adjustment, reliable equipment, effective cleaning, and decisions backed by the results of the oil itself.
Once the oil leaves the separation stage, a new task begins: protecting what has been achieved. In the third episode we follow the producer's storage and bottling mistakes, before the fourth episode moves on to the journey of shipping, handling and storage all the way to the table.
[1] International Olive Council — Quality Management Guide for the Olive Oil Industry: Olive Oil Mills. T.33/Doc. no. 2-4, 2006, Open original source
[2] University of California, Davis — Olive Oil Processing, Open original source
[3] CIHEAM Bari / OliveCulture — Guidelines for Hygiene and HACCP Implementation in Olive Oil Mills, 2023, Open original source
[4] Impact of industrial hammer mill rotor speed on extraction efficiency and quality of extra virgin olive oil. Food Chemistry, Open original source
[5] Modeling of volatile and phenolic compounds and optimization of the process conditions for obtaining balanced extra virgin olive oils. Grasas y Aceites, 2018, Open original source
[6] Oxygen as a Possible Technological Adjuvant during the Crushing or the Malaxation Steps, or Both, for the Modulation of the Characteristics of Extra Virgin Olive Oil. Foods, 2023, 12(11), 2170, Open original source
[7] Guerrini et al. The impact of vertical centrifugation on olive oil quality. Journal of Food Process Engineering, 2017, Open original source
