Most malaxers are made of a horizontal trough with spiral mixing blades, although some have vertical troughs. The vertical ones are generally known to produce a lower yield. Some are covered, and inert gases can thus be used to decrease oxidation.
Malaxing Time
A longer malaxing time increases the oil yield and helps the oil pick up minor components of the olives that can improve flavor. But a longer malaxing time allows oxidation that decreases shelf life; the oil has a higher acidity and peroxide level.
Heating
Heating the olive paste will decrease viscosity and improve the separation of oil and water. This increases the yield. Heating speeds oxidation and enzymatic breakdown of the paste, however, resulting in a lower quality product with higher acidity and peroxides. The oil has a shorter shelf life.
Using Inert Gases
To discourage oxidation, mixing tanks such as the Pieralisi "Genius" system can now be ordered with covers that contain an inert gas such as CO2 or Nitrogen, allowing increased yield and flavor without the danger of oxidation. Mixing chambers kept under a vacuum will accomplish the same purpose, but cannot remove as much oxygen as an inert gas blanket.
Adding Water
Water can also be added to facilitate the oil extraction but also results in lower quality oil with higher acidity and lower polyphenol level, hence a shorter shelf life.
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