How is vegetable oil made? I suspect that the cottonseeds, sesame seeds, corn, etc are placed into a crushing machine of some kind. But wouldn’t that produce more water than oil? And what happens to the solid stuff left over? Corn flour? Smushed sesame snacks? And how many seeds or corn kernals does it take to make a decent amount of cooking oil? Entire farm fields must be dedicated just to satisfying Mcdonald’s needs for fry cooking. How much work is it for me to end up with enough oil just to cook a Turkey once a year?
Okay, I’ll stop posting during lunchtime…
From what I remember from my Undergraduate Chemical Engineering courses, the oil is extraced using a Liquid-Liquid Extraction process.
What it means is that the crushed or even whole corn (depending on the diffusion constant / other factors) is first brought in contact with solvent A (something like a hydrocarbon, or other organic liquids) - the oil is soluble in this solvent and hence passes from the corn to the solvent.
Oil is recovered from Solvent A using distillation or other methods and then purified.
The solvent method is not the only way that oils are extracted. Depending on the particular source, the solvent method is only reserved for the lowest trash grade of oil. Olive oil, for example, has several grades. “Extra Virgin/Virgin” means that the oil was simply expelled by squeezing the olives. “Pure” means that the leftovers were subjected to heat and re-squeezed. Lower grades use solvents.
How corn oil is made
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Corn is “steeped”, that is left in a tank w/water and a bit of sulfur dioxide to “soften” it.
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The corn is broken up and centrifuged to separate the componenets: startch, fiber, gluten, and the germ. The corn germ is the little teardrop shaped nugget in the center bottom of the kernel. It has a high oil content.
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The germ is dried to remove excess water
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The germ goes through two sets of rollers, the first (called a flaker) to flatten the germ. The second (a cracker) flattens it so thouroughly as to rupture the cells of the germ.
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The flattened germ goes through expellers. The expellers move the germ through a constricting chamber with a screw. The chamber of the expeller is made of slotted metal that the oil can flow through. This removes only some of the oil.
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The expeller oil is put into a settling tank that separates water and solids from the oil.
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The meal that leaves the expeller goes to solvent extraction to get more oil from it, usually being process by an extruder first (which gives it a consistency that is more conducive to extraction).
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The meal is put on a large belt in an enclosed area (the extractor) and doused with hexane. The hexane dissolves the oil.
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The hexane/oil is removed from the extractor, and the hexane boiled off from the oil under high temperature and low pressure.
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The hexane is flashed off the germ meal under high temperatures (the desolventiser/toaster). The meal is used in animal feed.
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The expelled and extracted oils are combined. These are unrefined oil–dark and stinky. They go through two refining steps, deodorizing and bleaching. The nasties are flashed off under very high temps and low pressures. I don’t know how bleaching is done.
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Though not often done with corn oil, other oils (soybean) can go through another step, hydrogenation, where hydorgen is introduced in a reactor under temperature, turning double bonds into single bonds (hydrogenation). The amount of hydrogenation will affect the melting point. Lots of hydrogenation will result in Crisco.
This is it in a nutshell. There is a lot more detail than this, obviously.
Other oils, like soybean, often don’t have the expeller step because there isn’t enough oil to make it worthwhile. Frou-frou oils are only expeller pressed.
Oh, and a lot of corn goes down making corn oil. However, the corn oil is kind of a byproduct. The real reason for corn processing is that the starch (the majority of corn) is used to make high fructose corn syrup.
Most soybean field crops go to oil production, I believe.