Quality control for olive oil no longer begins once the olives are delivered to the mill. Especially now, with rising temperatures in the Mediterranean region, temperature management of olives immediately after harvest has become a critical factor influencing the final aroma and quality of extra virgin olive oil (EVOO).
Harvested olives experience a rise in fruit temperature due to daytime heat and storage in containers. This temperature increase affects enzymatic and oxidative reactions within the fruit, which in turn impacts the volatile components, phenolic compounds, and sensory characteristics after milling.
Hydrocooling is attracting attention as a solution to these challenges.
A research team from the Sant’Anna School of Advanced Studies, the University of Florence, and the University of Pisa in Italy conducted a three-year demonstration trial on rapidly cooling olives immediately after harvest before milling. In a commercial mill, cold water at approximately 1°C was sprayed directly onto the olives on a conveyor belt for about 30 seconds. They verified the feasibility of integrating this into actual milling lines while combining it with the washing process.
Reducing fruit temperature in just 30 seconds
The effects were clear. For the Frantoio variety, for example, the pulp temperature dropped from 21.7°C to 12.4°C in 2019, and from 24.8°C to 17.8°C in 2020. For the Leccino variety, it also dropped from 23.4°C to 17.2°C, and from 23.5°C to 14.1°C.
More importantly, it also influenced the subsequent malaxation process. The paste temperature of the hydrocooled olives remained generally 2–4°C lower compared to the control group.
Graph 1: Reduction in fruit temperature via Hydrocooling
果実温度（℃）
Frantoio 2019 21.7 ━━━━━━━━━━━→ 12.4
Frantoio 2020 24.8 ━━━━━━━━━━━━━→ 17.8
Leccino 2020 23.4 ━━━━━━━━━━━→ 17.2
Leccino 2021 23.5 ━━━━━━━━━━━→ 14.1
処理前 Hydrocooling後
The most notable effect is on “aroma”
Chemical analysis showed differences in response depending on the variety and year. While a decrease in free fatty acids (FFA) and peroxide value (PV) was confirmed for Frantoio, the effect on polyphenols was not necessarily a unidirectional increase.
However, a clear effect was confirmed in volatile organic compounds (VOCs).
Analysis using HS-SPME/GC-MS detected 31 types of volatile compounds. Statistical analysis allowed for a clear distinction between hydrocooled oil and control oil.
Of particular note are the C6 alcohols, which are involved in green grass, green, and fresh plant aromas. In Leccino, 3-hexen-1-ol increased approximately 6-fold, and 3-hexen-1-yl acetate increased approximately 20-fold. Meanwhile, some off-flavor-related compounds, such as ethanol and 1-penten-3-one, decreased.
This is an interesting result given the relationship between temperature and the lipoxygenase (LOX) pathway, which is crucial for olive aroma formation.
Graph 2: Changes in major volatile components in Leccino after Hydrocooling
相対値（対照区＝1）
3-ヘキセン-1-オール 1 ┃████ → 約6
3-ヘキセン-1-オールアセテート 1 ┃████ → 約20
※対照区を1とした相対的な変化
“Cooling” also leads to better shelf life
Even more interesting is the storage test. When stored for one year under optimal conditions (15°C, light-shielded bottles, headspace nitrogen flushing), the hydrocooled oil maintained better quality than the control oil.
In the control oil, oxidation progressed over time, and in the 2020 harvest, sensory defects such as “rancid” and “winey-vinegary” were confirmed after one year, with some cases losing their acceptability as extra virgin olive oil.
On the other hand, the hydrocooled oil maintained higher aroma intensity, bitterness, and pungency, and retained its sensory acceptability.
However, it is important to note here that Hydrocooling is not a technology that increases polyphenols in all varieties and under all conditions. The impact on phenolic composition and oxidation indicators varies depending on the variety, harvest year, and weather conditions.
Therefore, the essential value of this technology lies not in simple ‘cooling equals increased polyphenols,’ but in controlling the thermal history immediately after harvest and returning the fruit’s physiology to an appropriate temperature range before it enters the milling process.
New Quality Control in the Era of Climate Change
Until now, discussions on milling technology have focused on processes inside the mill, such as malaxation temperature and time, decanters, and separators.
However, with extreme heat becoming the norm, the temperature history itself from ‘harvest to transport, washing, and crushing’ may become a key quality control parameter.
Hydrocooling has the potential to be introduced while utilizing existing washing processes, and its feasibility in commercial mills has already been confirmed.
Of course, practical challenges remain, such as capital investment, water usage, hygiene management, energy costs, and wastewater treatment. Additionally, it is necessary to set optimal cooling temperatures and processing times according to variety and harvest conditions.
Nevertheless, the concept of ‘cooling harvested olives to an appropriate temperature as quickly as possible’ is extremely rational for olive-growing regions facing rising temperatures due to climate change.
In future EVOO production, it may be necessary to design not only ‘when to harvest’ but also ‘at what temperature to deliver the harvested olives to the mill and at what temperature history to crush and malaxate them.’
Hydrocooling is precisely one of those new quality control methods that deserves further attention in the future.
Source: Teatro Naturale