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Listello mill for olive oil processing


Key words Milling, grinding, mill, milling machine, olive oil, olive oil processing, pressing, first pressing, immediate pressing
Latest version 2011/09/22
Completed by IRTA

How does it work?

Primary objective Improve the efficiency of olive oil extraction
Working principle First pressing is the third step in olive oil processing, after olives sorting and cleaning (air and water). This operation is a mix of grinding and breaking the whole olive (incl.pit) to facilitate the extraction and separation of the oil contained.
2 2 4 physical effects.JPG

Pic 1. Infography with physical effects during olive milling and kneading (© Agustí Romero, 2011); Molturación y batido: efectos físicos (Milling and kneading: physical effects); Rotura de células (cell breaking); unión gotas aceite (olive oil droplets joint)

The main milling goal is to crush as many olives as possible in minimum time. Both physical processes and chemical reactions happen while crushing, including oil droplets separation, temperature increase, oil-in-water and water-in-oil emulsion formation, minor components dilution (polyphenols, waxes, pigments, sterols, water, alcohols, terpenes...), enzyme activation (LOX and more) and so on. Emulsions is the most problematic aspect, as only non-emulsified oil can be physically separated. Stable emulsions created during crushing require further processing steps, such as kneading and centrifugation. Historically stone mills ranging from 300-800 kg/h (private producer mill) and 5.000-10.000 kg/h (big cooperative) were used for milling operation. Nowadays, new mills are used, for instance the Listello mill which has a maximum grinding rate of 12.500 kg/h. The Listello mill is made using metallic materials, in a shape of a hammer or gearwheel.
Beltrán et al. (1) have studied the effect of milling degree (granulation level) and the hammers rotation speed in Listello mill, using Picual olive variety. Best results were worked out through a Listello mill of 5mm size and low rotation speeds of 2000 rpm; High speed rotations decrease the final performance of the milling process. Milling conditions do not affect the oil quality, but higher levels of peroxides are observed as rotation speed increases. K225 (average ratio to measure the bitterness level of oily polyphenols) is higher when the olives are processed through an intermediate granulation level, while lowest concentrations and less bitter-taste oils are obtained using the smallest Listello mill. Chlorophilic pigments and carotenoids levels decrease if milling grade increases and rotation speed rate decreases.

Other effects quoted using Listello system: - At higher rotation speed rates, performance is lower - Increasing the criba speed and the rotation of the hammers, the polyphenol content is reduced, lowering the stability of the oil - The lower the kneading temperature, the lower the polyphenol concentration in the olive mass.

2 2 4 listello mill.jpg
2 2 4 doble criba mill.jpg

Pic 2. Infographies of Listello and Doble criba mills (© Gabriel Beltrán, IFAPA), where molino means mill

2 2 4 Listello detail.JPG
2 2 4 Cribas detail.JPG

Pic 3. Infographies of milling system and criba mills (© Gabriel Beltrán, IFAPA)

Additional effects
  • Less oil-in-water emulsion
  • Oil paste is less heated
  • Lower extraction of pungent polyphenols
  • Less bitter-taste oils (by Listello compared to Criba mill)
  • A bit pungent taste (by Listello compared to Criba mill)
Important process parameters milling time, milling degree, rotation speed, milling temperature, mill type
Important product parameters olive variety, olive ripening

What can it be used for?

Products Olive
Operations Grinding, milling, pressing
Solutions for short comings
  • Better oil extraction, as the the oil pressing process is optimized
  • Allows faster and lower temperature kneading (step after first pressing)
  • Decreases product loss
  • Lower energetic consumption
  • Less bitter-taste oils

What can it NOT be used for?

Other limitations No limitations, in comparison to standard mills
Risks or hazards No hazards, in comparison to standard mills


Maturity Some cooperatives with a good performance use nowadays such mills. Technical support is available too.
Modularity /Implementation New mills can replace old ones without any technical problem.
Consumer aspects Consumers usually prefer not very pungent or bitter virgin olive oils (3).
Legal aspects No new legal aspects expected. Please check local legislation.
Environmental aspects
  • Lower energetic consumption
  • Decrease in product loss

Further Information

Institutes IRTA-Mas Bover, IFAPA, CSIC - Instituto de la grasa, ISE
Companies Pieralisi
References 1. Beltrán G., Aguilera MP., Allouche Y. & Jiménez A. (2011). Efecto de las condiciones de molienda del molino listello sobre el rendimiento del proceso y las características del aceite- Effect on milling conditions of Listello mill on process performance and oil properties. XV Scientific-technical symposium of olive oil. Jaen, Spain, 11-13th May 2011.

2. Beltrán G. (2010). El sector del olivar en Europa: una visión estratégica vinculada a la innovación - The olive sector in Europe: an strategic view related to innovation. Jornadas Emprender e innovar en el sector del olivar. Baena, Spain, 22th November 2010.

3. Guerrero, L., Claret, A., Chaya, C., Fernández-Ruiz, V., Romero, E. & Viejo, J. (2011). Los consumidores y la cultura del aceite de oliva. In: Beyond Extra Virgin (BEV) - 5th edition. Oportunidades para el aceite de oliva: el valor de la excelencia. Córdoba, Spain, 8-10th June 2010.

4. Romero A. (2011). Millores tecnològiques aplicades a l’oli verge d’oliva: materia prima, extracció, celler, gestió de subproductes i residus. Jornada sobre innovació a la industria agroalimentària – Technological improvement for virgin olive oil: raw material, extraction, mil, by-products management and wastes. Barcelona, Spain, May 2011.

5. Romero A. (2011). Retos de la industria del aceite. Calidad, procesos de elaboración, vertidos, comercialización - Challenges of the olive oil industry challenges. Quality, production processe, waste spills and commercialization. Sevilla, Spain, September 2011.

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Created by Hte irta on 28 February 2012, at 10:23