You use it for your hair, to cook food, to grease creaky door hinges, in paints, in lotions and what not. Yes, we are talking of oil – the multi-utility liquid that has found use in so many daily activities that we don’t even give it a second thought. But for now, we will talk only about sunflower oil, which is used as a cooking medium. You must think what could possibly be so complex about making sunflower oil? Just mash the seeds together, and out comes the oil. But it is so much more than that. To begin with, there are three types of sunflower oil seeds. NuSun, Linoleic and High Oleic. And it is the sunflowers that produce the little black seeds which are preferred to make oil. There are two types of sunflower oil, warm pressed and cold pressed. Cleaning and grinding:
Cleaning and grinding: The seeds are first cleaned by passing over magnets – this helps pick out metals or other material – and then deskinned. The cleaned seeds are now ground by hammer mills into a powdery form and then heated to 170 degrees Fahrenheit to make it easier for the oil to be secreted.
Pressing: The heated mix is now pulverised using a screw press. As the pressure increases gradually, the oil starts to trickle out of the seeds.
The remains of the day: Once the oil is extracted, it leaves behind solid remnants called oil cakes. To ensure maximum yield, these cakes are processed using solvents like hexane. Hexane helps to dissolve the oil out of the cake – it simply evaporates from the extracted oil and can be reused. As for the oil, it is boiled using steam so if there is any trace of hexane left, that evaporates too.
Refining: The oil at this stage is of a slightly odd colour, smell and taste. What it needs is refining to remove these. So it is heated between 107-188 degrees Fahrenheit with an alkaline substance like sodium hydroxide or sodium carbonate. They form soap from the unwanted fatty acids which can be removed by a centrifuge machine (it rotates rapidly to create centrifugal force that separates substances of different densities). During refining, the oil is also degummed by treating it with water at 180-200 degrees Fahrenheit. This process removes the gritty particles in the liquid. Next, the oil is bleached by filtering it with fuller’s earth (which is a type of clay for making liquids clearer), activated carbon or activated clays that absorb the pigmentation from the oil. Finally, the oil has to be deodorised. This is done by passing steam over hot oil in vacuum between 440-480 degrees Fahrenheit. This process refines the oil’s taste too. Usually a small amount of citric acid is also added to deactivate metals that may cause oxidation of the oil (and thus reduce its longevity). From here on, preservatives are added to the oil and it is packaged for sale. In the cold pressed method, the mashed seeds are not heated before being pressed.
And it gets better... Like any other process, this also creates by-products. Fortunately useful ones. The oil seed cake over is used as livestock feed because it is high in protein and other nutrients. It can also be used as a fertiliser.