Cold-pressed and Virgin Oils
Cold-pressed or virgin oil utilizes unshelled, occasionally also hulled seeds or fruit. The oil is generally made through mechanical means of pressing, without any heat input.
Only the press cake remains with a residual fat content of 10-14%. After pressing, the oil is filtered to remove any remaining seed or fruit particles.
Through this careful preparation process, the distinct original taste of the oil as well as vitamins, unsaturated fats and other desired, secondary ingredients can be preserved.
This process is obligatory for all ecological oil processing, but is employed in the conventional sector as well.
Most virgin or cold-pressed oil products keep very well for extended periods of time.
If kept in the refrigerator, these oils will show signs of white streaks (the waxes flocculate). This is by no means a defect, but evidence that no further processing took place after the initial pressing of the oil.
However, there are virgin and cold-pressed oils that do not show streaks when kept in the refrigerator. These oils were “winterized” in the oil mill. This entailed a temperature decrease to 8 degrees Celsius for a period of 5-10 hours. The waxes crystallized and were filtered out.
Refining of Cooking Oils (Physical Refining)
When refining organic oils, organic citric acid is used in place of sodium hydroxide. The following deodorization (the oil is steam cleaned) removes free fatty acids to a mere remainder of 0.1%.
Cleaning of the oil by means of steam takes place at various temperatures ranging between 130-220 degrees Celsius.
A significant reduction of environmental pollution is the main advantage of physical refining.
Fully refined oils are oftentimes labeled as RDBW (refined, deodorized, bleached, winterized) and are not as durable as cold-pressed, virgin oils.
Furthermore, refined oils are tasteless, nearly colourless, and extremely heat-resistant (high oleic variety) making them the ideal cooking choice.
Desired secondary ingredients such as vitamins, unsaturated fats are rarely more prevalent in refined cooking oils.
All organic oils are required to be refined using the physical refining method.
Another possibility is partial refining (only deodorized or light steaming). The customer has the option to choose the temperature themselves to a great extent. However, fundamentally, it has to be taken into consideration that the oil is more tasteless the higher the temperature and the longer the exposure time.
Most cooking oils, with the exception of rapeseed oil for example, contain waxes. Wax crystals will form and give the oil a cloudy appearance with refrigeration. The process reverses again at room temperature. This natural process can be counteracted with winterization, which entails cooling the oil for several hours to allow the waxes to crystallize. The cold, cloudy oil is then filtered, the solid waxes remain in the filter and the oil will now be clear even at low temperatures.
Extraction of Oils (Exclusively for Conventional Products)
In this method, the oil contained in seeds and fruit is displaced through the use of a chemical solvent (usually hexane). The hexane-oil-mixture is heated to a minimum of 140 degrees, which causes the hexane to evaporate and the plant oil to remain. In place of hexane, the use of crystallized carbon dioxide (CO2) is common as well and more environmentally friendly than hexane extraction. In comparison to press cakes, the by-product – extraction meal – still contains 2% rest fat rendering a higher oil yield.
More than 90% of plant oils worldwide are produced through extraction. However, all of these oils require to be refined or cleaned further before use.
During chemical refining, lecithin is withdrawn from the oil before adding phosphoric acid for settling and filtration. Next, sodium hydroxide is added to the oil, that reacts with the free fatty acids contained within the oil and precipitates in the form of sodium soap. In order to remove colour and all undesirable content such as pesticides, peroxides, or compounds formed during the extraction process, the oil is then bleached with bleaching earth and/or activated carbon. The final step is steaming or deodorization to remove nearly all flavouring agents.