Contents 9 sections
Plant oils differ not only in their fatty acid composition but also in the way they are produced. The extraction method has a decisive influence on which natural constituents are retained in the oil and which changes take place during processing.
Anyone wishing to assess the quality of a plant oil should therefore consider not only the plant species but also the method of extraction and processing.
Plant oils are more than just mixtures of fatty acids
In addition to their fatty acids, plant-based oils contain numerous natural minor lipid constituents. These include, among others:
- Tocopherols (vitamin E compounds)
- Phytosterols
- Lecithin
- Carotenoids
- Chlorophyll
- Aroma compounds
These natural constituents influence the colour, odour, taste and properties of an oil. Depending on the manufacturing process, they are retained to varying degrees.
Cold pressing: gentle oil extraction by mechanical pressing
In cold pressing, the oil is obtained from seeds, kernels or fruits by purely mechanical means. Although frictional heat is generated during pressing, no additional heat is applied.
After pressing, cold-pressed oils may only be cleaned by filtration, decanting or centrifugation . No chemical solvents or extensive processing steps are used. As a result, the oils largely retain their natural composition, including their fatty acids and minor constituents.
Typical characteristics of cold-pressed oils:
- odour characteristic of the variety
- characteristic taste
- natural colour
- high content of natural minor constituents
- individual raw material profile
Higher oil yields through warm pressing and extraction
Mechanical pressing cannot recover all of the oil from a seed or fruit. To increase the yield, higher temperatures are often used in industrial production.
The oil still contained in the press cake after pressing can then be extracted with solvents, usually hexane. This extraction makes it possible to achieve very high oil yields. The crude oil obtained in this way is generally not yet suitable for further use and is therefore processed further.
CO₂ extraction as an alternative extraction method
A special form of oil extraction is extraction with supercritical carbon dioxide (CO₂). Under high pressure, carbon dioxide behaves like a solvent and can dissolve fat-soluble constituents from the plant material. Once the pressure is released, the CO₂ evaporates without leaving any residue.
The process is regarded as particularly gentle and allows high-quality speciality oils to be obtained. Due to the technical effort involved, however, it is used far less frequently than conventional pressing or extraction methods.
Why plant oils are refined
A large proportion of the plant oils produced worldwide are refined after extraction. In this process, certain minor constituents are removed in order to improve shelf life and obtain as uniform a product as possible. Refining takes place in several steps:
- Degumming – mucilage and lecithins are removed.
- Deacidification – free fatty acids are reduced.
- Bleaching – special adsorbents remove colourants and minor constituents such as chlorophyll or carotenoids.
- Deodorisation – odour and flavour compounds are removed at high temperatures.
The result is oils that are largely neutral in odour and taste, with high storage stability.
What effects does refining have?
Refining does not only remove undesirable minor constituents. At the same time, components that occur naturally in the oil are also lost – depending on the oil, these include lecithins, tocopherols, phytosterols, colourants and aroma compounds.
Refined and virgin oils differ not only in taste and colour but also in their natural profile of minor constituents.
Virgin and refined oils compared
Plant oils can therefore not be assessed on the basis of their fatty acid composition alone. The degree of processing also plays an important role.
| Virgin oils | Refined oils | |
|---|---|---|
| Processing | gently processed | refined in several stages |
| Taste & aroma | characteristic aroma | neutral taste |
| Colour | natural colour | lighter colour |
| Minor constituents | high proportion of original minor constituents | reduced range of minor constituents |
| Storage stability | depends on the variety | high |
The two types of oil have different properties and areas of application.
What the quality of a plant oil depends on
Various factors are relevant when assessing a plant oil:
- Plant species
- Fatty acid composition
- Natural minor lipid constituents
- Extraction method
- Degree of processing
Only the interplay of these factors determines the individual profile of an oil.
Conclusion
The production process has a decisive influence on the quality and composition of a plant oil. Cold pressing, extraction and refining result in different oil profiles and influence which natural minor constituents are present in the finished oil.
Looking at the fatty acids alone is therefore not enough to evaluate a plant oil. The minor lipid constituents and the method of extraction and processing are just as important. Only together do they give the complete quality profile of a plant-based oil.
Quoted from Ruth von Braunschweig: Plant oils. Über 50 starke Helfer für Genuss und Hautpflege!. Stadelmann Verlag, 2025. Chapter I ‘Oil Extraction and Quality’, pp. 48–51.. ISBN 978-3-943793-68-0 – By kind permission of Stadelmann Verlag.
