Good manufacturing practices

The first salient point in DONNA LISA’s production process is that the olives are still crushed with granite millstones and then, later on, the oil is extracted with a centrifuge rather than with a press.  The granite millstones and centrifugal extraction ensure the oil’s purity and virginity, reducing human intervention to a minimum.  In actual fact, the centrifugal system means that it is possible to skip completely the pressing phase, thus avoiding a whole industrial process.

The other important point about production is that DONNA LISA uses cold milling.  The temperature of the olive paste is kept at 29°C-30°C, which is the perfect temperature for extracting the oil.  Working at higher temperatures alters the quality of the oil, and at lower temperatures, the oil starts to thicken because of the cold, thus making extraction less efficient.

Guidelines for best results

The guidelines for best production practices, summarized here, bring together some basic rules for making extra virgin olive oil, and a series of parameters for controlling the process in order to guarantee established quality standards.

The quality of the olives :
Checking the quality of the olives is the first crucial point of oil production.  The quality of the olives is surely the basic premise for obtaining a good quality oil.  The quality of the olives can be attributed to a series factors, such as: variety, state of maturation, integrity of the fruit and fermentation levels.

Transportation and storage of the olives :
Damage from mechanical sources or stocking with possible rises in temperature must be avoided during transportation and storage of the olives.  Improper handling during these phases can, in fact, cause enzymatic reactions, and encourage bacterial and mildew growth. In order to keep mechanical damage to an absolute minimum, aerated crates should be used instead of the traditional sacks. Direct contact with the ground should be avoided.  The olives should be stacked in perforated, 300kg (max) cases, and milled as soon as possible after harvesting (within a maximum of 2 days). Sweetening the oil by prolonging the wait before milling is inadvisable because it can lay the olives vulnerable to quality defects (oil deposits, mildew, fermentation), which, in the light of recent regulations, would downgrade the end product to “virgin” or “lampante”.  To obtain a sweeter oil it is generally advisable to harvest the olives at a more advanced stage of maturation.

Defolation:
Leaves and twigs should be removed out in the field, and their weight should not exceed 1%-2% of the total load.  Too many leaves and twigs can, in fact, give a bitter, leafy flavour to the oil, which, for certain varieties, can further compromise their suitability for consumption.  Furthermore, excessive chlorophyll released into the oil can accelerate oxidation if stored in the light.  With more mature olives, however, a higher percentage of fresh leaves can improve the specific attributes of the oil.

Washing:
Drinking water should be used and changed frequently.  Washing the olives is necessary, for the sake  of quality standards, above all when the olives have been spoiled in order to remove the smell of impurities or fermentation.

Milling:
Depending on the milling process, the olives release a high quantity of bitter substances into the oil.  Based on experimental data, it is has been possible to create the following scale in descending order of  bitterness levels created by different milling processes: hammer-crusher with bi-directional rotating grills → hammer-crushers with fixed grill → high revolution disk mills → hammer-crushers with rotating grill → mixed crushers (rollers with low revolution disks) → granite millstones.

Gramolation:
In this phase, the pulp is turned over and over very slowly in order to homogenized the mass so that it can be separated more easily from the oil. The temperature of the olive pulp and process water should not exceed 29°C-30°C. Settling and separation should last no longer than 90 minutes in order to avoid losing phenol compounds to oxidation, and with them,  important aromatic substances.  This also avoids the oil becoming rancid from the increase in peroxides.

Extraction process :
The importance of this operation is not to be underestimated, even if it is less influential than the milling process and the separation temperature.  According to the amount of water that is added to the pulp for centrifuging, the concentration of bitter substances like aglicon and oleuropein, which is very soluble in water, changes as the water and oil become separated. The following is a scale that grades the phenol compound content measured in different extraction processes, whilst using the same method of milling and separation: pressure → percolation → bi-phase centrifugation → tri-phase centrifugation. As contact with water increases, the levels of bitter substances decrease.

Storage:
Olive oil should be kept in the dark during storage, and in completely full, hermetically sealed containers.  Certain “traditional” containers such as terracotta jars, and zinc or fibreglass containers are not suitable for efficient storage. Stainless steel canisters are excellent for storing oil. Oil should be stored at a temperature between 12°C and 18°C.  At temperatures below 10°C, the triglycerides begin to crystallize, first starting with the saturates, and then the rest of the fat. After thawing, this can cause:

Oils with a higher content of saturated and mono-unsaturated fatty acids (eg.: oils from green olives) crystallize more easily than oils from mature olives, which are usually rich in linoleic acid and other fluids. Temperatures over 20°C accelerate biochemical changes in the oil, especially the oxidation process which makes the oil turn rancid. Furthermore, in unfiltered oils, enzymatic reactions take place more quickly, causing a series of problems.  The free acid content can rise, and the phenol compounds breakdown, making the oil sweeter.  Bacteria, yeasts and fungi can start to ferment, producing soluble compounds such as acetic acid and ethyl acetate.  These substances negatively influence the aroma of the oil, making it smell winy, or fermented, or even putrid.

Decanting and filtration:
The oil should be separated from any solid impurities (dregs) and water within three months by means of decanting.  Thereafter, it should be transferred into clean, dry containers.Filtered oil is a basically stable substance,  because filtration blocks the natural break down of the phenol complexes by enzymes. This stops the oil from gradually turning sweet during storag