‘Blown oil’ is the term used to describe fatty oils produced by blowing hot air, at a temperature of 100-150 ° C, into a product, for several hours. Although, in principle, any vegetable oil can be used to produce blown oils, refined rapeseed oil (rapeseed oil) or refined flaxseed oil is used in most cases. In both cases, the final products are called ‘blown rapeseed oil’ or ‘flaxseed oil’.

When hot air is blown, at a temperature of 100-150ºC, in a product, for several hours, the fatty acids contained in the oils undergo a process of autooxidation. This also happens when the vegetable oils are exposed to the air, but in this case the autooxidation takes several months. The blown oils are clear and reddish liquids, drying, resistant to bad weather and that give off a characteristic odor. They are viscous and sticky, not soluble in water, but soluble in lipophilic solvents.

Compared to refined oils, the viscosity in the blown oils is much higher, but it can be adjusted by altering the blowing time. The blown air leaves the product with a fatty acid composition that differs from that of the oil used in the production. For example, blown rapeseed oil contains a large amount of oleic acid (60-75%) and approximately equal proportions (4-9% and 5-8%, respectively) of palmitic and linoleic acid, with a little stearic acid (2-5%). The other fatty acids are linolenic acid (max 2%) and erucic acid (max 6%).

Blown oils are used in the dye industry as well as in coating materials. In the detergent industry, blown oils are used in the production of active substances for washing, as they have excellent antifoam characteristics. It is for this reason also that the blown oils are used in the metal industry as flotation water collectors.