Why does olive oil separate from water

The oil obtained is not perfectly transparent and clean, but slightly turbid, opaque. It is perfectly edible, raw and emanates a very intense scent of olives. By Trecciano. In Tutorial. Leave a Comment. Save my name, email, and website in this browser for the next time I comment. Harvest in Trecciano, Chianti 11 December Vin Santo from Chianti 30 January However, after stripping, a loss of some VOO key odorants i. Stripping appears to be promising for VOO, but other studies are required to deeply understand its effect on the product.

Inert centrifuges and nitrogen stripping could be useful to protect VOO from oxidation, but they cannot prevent the losses of phenolic compounds due to the use of process water. In recent years, some strategies to avoid vertical centrifuge have been implemented.

Altieri and coworkers propose an online sedimentation approach [ 22 ]. Sedimentation is an ancient procedure used to clarify vegetable oils, requiring large basins and long times. Some small olive mills, producing high quality olive oils, start to filter the VOO directly from the decanter, avoiding the vertical centrifuge.

This approach requires a careful sizing of the filter to equal the working capacity of the decanter. If the filter is well sized, this approach seems to be able to protect the VOO quality, avoiding the introduction of oxygen and water due to the vertical centrifugation [ 14 , 23 ]. Filtration is one of the most debatable steps in olive oil production.

Some consumers appreciate veiled olive oils recently produced, while others prefer filtered olive oil. Filtration could be considered one of the simpler and spread solid-liquid separation. During filtration, a suspension is forced into a porous medium able to hold the solids and let the liquid pass through. The liquid will be consequently clearer. Two theoretical models explain the filter behavior: surface and depth filtration. In the former, the porous medium has holes smaller than the suspended particles.

In the latter, the separation is due to the adsorption of particles into the porous. In this case, the porosity is greater than the retained solids. The division into surface filters and depth is a simplification of what happens in real filters where, usually, both theoretical models occur simultaneously. For instance, the layer of solid particles that are deposited on a surface filter exerts increasingly greater depth of action as it increases in thickness [ 24 , 25 ].

This speed is governed by the equation of Hagen-Poiseuille:. The pressure difference is theoretically proportional to the speed with which the process takes place. Actually, the physicomechanical characteristics of the solid residue of olive oil divert from linearity, and the pressure increase is often not proportional to the increase in the rate of filtration. From the formula, it is easy to understand the importance of the correct size of the filter, hence the correct determination of the filtering surface A.

Another important parameter for VOO filtration is the temperature of the mixture during the process. Temperature does not appear directly in the equation of Hagen-Poiseuille but strongly influences the viscosity. The higher the temperature, the lower the viscosity of the oil to be filtered. This effect is caused by the progressive increase in the amount of solids on the filter medium [ 27 ]. Many filtration technologies are adopted to remove solids and water from VOO: conventional systems such as filter tank, filter press [ 27 ], cross-flow systems [ 28 ], inert gas flow filtration systems, and filter bags, as reviewed by Frankel et al.

The VOO is introduced into a vessel lying on the bottom of one or more layers of textile fiber. The filtered oil is collected in a second vessel placed at a lower level than the first. This type of filtration is carried out without pumps, using the gravity acceleration. The cotton filter is a cheap and easy solution. The main drawback of cotton filter is related to the very long time required for the operation. The pressure difference between the two parts of the filter is low due to the force of gravity and by the hydrostatic pressure of the column of oil.

The filtering surface is limited. During this operation, the oil is exposed to oxygen and consequently to the risk of oxidation [ 27 ].

The most common filter used in small- and medium-sized production companies of VOO is the filter press. Filter press consists of a series of flat chambers placed vertically next to each other. The chambers are composed of a plate used for support and turbid oil distribution, and by the filter medium, composed of filter sheets.

To avoid loss of oil when the pressure rises, chambers and filter sheets are adhered to each other through a central screw and two metal plates. The filter is dimensioned by choosing the appropriate number of filter media sheets. They usually have a square shape and size between 20 and cm [ 25 ]. The filter sheets for filter press are depth filters and consist mainly of cellulose [ 23 ].

To reduce the use of sheets and the VOO losses, the filter press could be coupled with stainless steel pre-filters [ 23 ].

On a larger scale, Kieselguhr filters are often used. In this kind of filters, the filtration adjuvant is continuously added to the olive oil suspension. That colloidal suspension gives rise to highly compressible deposits, and the adjuvant confers to the deposit stiffness and porosity to obtain good permeability and ensure higher flow throughout the filtration cycle. However, in the last years, the cross-flow filtration membrane filtration began to spread [ 28 ].

Membrane filtration is a very common practice for seed oils, which recently has also been proposed for the VOO. Membrane filters, when compared with other filtration systems, provide some benefits.

For instance, they eliminate the filtration adjuvants. Usually, adjuvants retain VOO, causing some losses. Furthermore, the disposal of these adjuvants could be problematic. In the Kieselguhr filtered oils, it is common to find traces of some filter aids; this does not happen in the membrane-filtered oils. In addition to the solution of these problems, the membrane filtration allows to remove traces of heavy metals, such as copper, manganese, and iron, which sometimes contaminate the oils.

The cross-flow filters are typically surface filters, characterized by a high efficiency of retention at low porosity [ 28 ]. Filtration affects chemical composition of VOO, changing the minor compound concentration and olive oil stability during storage [ 30 ]. Lower stability and greater susceptibility to alterations are attributed by some authors to cloudiness. However, water and suspended solid particles contain antioxidant compounds.

The aromas are created in these two steps through the action of fruit enzymes. Afterwards the paste is pumped into an industrial decanter where the phases will be separated. Water is added to facilitate the extraction process with the paste. The decanter is a large capacity horizontal centrifuge rotating at approximately rpm. Inside the decanter's rotating conical drum there is a coil that rotates a few rpm slower, pushing the solid materials out of the system.

The separated oil and vegetation water are then rerun through a vertical centrifuge, working at nearly rpm that will separate any other small quantities of oil from the water.

The Sinolea method is a cold pressing milling system, which employs no pressure or added water and was first introduced in It consists of a stainless steel comb or set of blades that dip into the olive paste. At every dip the comb or blades is covered in a thin layer of oil, which then gets wiped off into a bowl. The concept is borrowed from a very simple law of physics: liquids with different molecular cohesion have different surface tensions.

This can be understood with a simple home experiment. Place water in a cup and then put some oil in it. Dip a stainless steel fork into it and notice the oil will cling onto the metal but not the water. Patiently, let the oil drip off the fork into another empty container and you will have a separate container of only Olive Oil. It takes a very long time, but the argument is that the oil is more superior in quality due to less stress imposed on it during the process.

In addition to saving the oil paste from too much mechanical handling, the Sinolea method acts as a mild bouquet and flavour enhancer in extra virgin Olive Oils by allowing them to retain the highest percentage of natural antioxidants and all of the various components that contribute to an Olive Oil's quality. Olive Oils extracted with the Sinolea Method tend to be more costly because of the time involved, the small quantity of high quality oil produced, and the larger amounts of olives required compared to the other methods.