CH17 THE OLIVE OIL REFINING PROCESS
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hydrocarbons (PAHs), formed during pomace drying, 5 to 10% activated carbon is added to the bleaching earth, which greatly increases the absorption capacity of the mixture. Activated carbon, in fact, is extremely porous and has an enormous surface area per gram with great absorption capacity. Bleaching is carried out in discontinuous operations, under vacuum, at a temperature of 90–110 ∘ C for 20–30 min, with low speed agitation in order to maintain the bleaching earth in suspension. The suspension is then cooled to 70 ∘ C and the bleaching material is separated from the decolourized oil by filtration with filter-plate or leaf filters.
Deodorizing The aim of the deodorizing operation is the removal of off-odours that were formed in the previous operations of the refining process. Deodorizing is the last operation of the process. It is a continuous vacuum distillation with steam stripping of volatiles.
17.4 The physical refining process The physical refining process differs from the chemical refining process by the fact that the deodorizing operation is carried out in conditions (higher temperature and lower pressure) that allow not only the volatile, bad-smelling compounds, but also the free fatty acids, to be removed. With physical refining, the chemical neutralization operation is avoided. The neutralizing effectiveness of the physical process is very good. The free acidity of the oil, after the physical refining process, is in the range of 0.03–0.05%. The conditions of the deodorizing operation for the two cases are compared in Table 17.2. Table 17.2 Comparison of the conditions of the deodorizing operation in the chemical and physical refining processes. Operating conditions
Chemical refining
Temperature Pressure Steam Time of the operation
220–230 ∘ C 3 mbar 10 kg per ton of oil 60 min
Physical refining 240–250 ∘ C 2 mbar 15 kg per ton of oil 60 min
17.5 The quality and uses of refined olive oil An in-depth discussion of the effects of solvent extraction and refining on the various components of olive oil is beyond the purpose of this handbook. Only a few points will be given to indicate the differences between refined and extra-virgin olive oils.