Cold pressing
The cold pressing is the central step in the production of cold-pressed vegetable oils in oil mills . In cold pressing, among other things, so-called native or natural vegetable oils are produced. The cold pressing process is used as the first processing stage in central oil mills on an industrial scale; in decentralized oil mills it is the only processing stage.
Procedure
With cold pressing, the raw materials, possibly in crushed form, are only pressed out in a single operation. A separation process can then take place. In contrast to this, several work steps are used in hot pressing until the oil is finally completed, including the use of chemical additives. However, the term cold pressing alone does not allow an exact statement about the temperatures reached during the pressing. With soybean oil and corn oil , temperatures of up to 75 ° C are possible, but 45 ° C should not be exceeded for gentle pressing. In the production of pumpkin seed oil and argan oil , the high-fat seeds are roasted before pressing, which only creates aromatic substances characteristic of these oils, but the "naturalness" ( "native oil" ) attributed to cold pressing is lost.
Different tools are used depending on the requirements and technical development. Screw presses have been in use since ancient times, whereas a screw press is usually used in modern oil mills . As with the screw press, only low frictional heat is generated in it during the pressing out of the oil products. In addition, the productivity is significantly higher compared to the screw press. The adjustment of the screw press (e.g. the selection of the press nozzle) has a decisive influence on the temperature of the oil during the pressing process. The change between compression and relaxation of the pressed material is decisive for the smooth running of the pressing process. The relaxation promotes the oil drain from the pressed material to the strainer . The trub oil or crude oil emerging from the press still contains approx. 0.5 to 0.6 percent by weight of solids (particles), which accelerate oil aging and, in technical use, can lead to filter clogging or increased wear on materials. It is therefore cleaned of sediments and suspended matter by sedimentation (allowing it to settle) and filtration.
Legal basis for olive oil
Regulation (EU) No. 29/2012 regulates the permitted use of the terms first cold pressing and cold extraction for olive oils in Articles 5a and 5b. The indication of first cold pressing is therefore only permitted if the olive oil was obtained at a maximum of 27 ° C by mechanical pressing in a traditional extraction system (Article 5a) . The indication of cold extraction is only allowed if the olive oil was obtained at a maximum of 27 ° C by percolation or centrifugation (Article 5b) . This has no influence on the quality classifications such as “extra virgin” or “native”, as the content of free fatty acids is decisive. For example, the so-called lampante oil is an olive oil obtained by cold pressing, but not approved for human consumption due to its increased content of free fatty acids.
Result
In the production of cold-pressed oils, all ingredients of the starting products can be retained at low temperatures. These influence the quality criteria such as taste, smell, color and vitamin content. The taste of cold-pressed oils is determined by the oil fruit / seed used. In contrast to this, vegetable oils that are produced by hot pressing and refining are tasteless, as the easily perishable and therefore undesirable components that are important for nutrition and taste are removed from the oil.
Properly produced vegetable oils from cold pressing are suitable as vegetable oil fuel. However, since i. d. As a rule, there is no subsequent separation of engine-damaging or emission-generating accompanying substances such as phosphorus , calcium and magnesium , a perfect quality of the raw material and the production process is a prerequisite for a high-quality and standard-compliant biofuel .
literature
- Edgar Remmele, Bernhard Widmann: Vegetable oil production in small plants. Chapter 13.2.2, In: Martin Kaltschmitt, Hans Hartmann and Hermann Hofbauer (eds.): Energy from biomass: Fundamentals, techniques and processes. 2nd edition, Springer Verlag, 2009, ISBN 978-3-540-85094-6 , pp. 725-735.
Individual evidence
- ↑ Quality assurance in decentralized vegetable oil production for the non-food sector - technological research and development of quality assurance measures. Reports from the TFZ, No. 12. ( PDF ( Memento of the original dated May 8, 2010 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ).
