“How do they make cooking oil?”

Early Roman oil press (Image by Eitan f via Wikipedia)

Fun in the kitchen week continues with a look at another ingredient in homemade play-doh: Cooking oil.

There are lots and lots of kinds of oils in the kitchen, each with their own fascinating manufacturing account, I’m sure, but for the purposes of this entry, I’m going to focus on the kind we dribbled into our Play-doh pot: plain old vegetable oil.

To make vegetable oil, you extract liquid oil from various plants, such as olives, sunflowers, peanuts, and corn. Although it’s possible to get oil from many parts of the plant, most frequently, oil producers use the seeds.

There are several ways to extract the oil. Although many whole food stores extol the virtues of the traditional cold-pressed method, in the earliest of days, heat was integral to the process. Once upon a time, people in Mexico and North America used to mash peanuts into a paste, boil it in water, and skim off the oil as it rose to the surface. Early Africans used a similar process to make coconut and palm oils.

Today, most oils are made using a press and/or chemical solvents. How Products Are Made gives a good overview of the process.

In a nutshell, manufacturers first prepare the seeds (or in the case of olive oil, the fruits) by cleaning them and grinding them. Then they run the ground seeds through a press to extract the oil.

If the manufacturer is using the cold-press technique, the press will be kept below 120 degrees Fahrenheit (49 degrees Celsius) to avoid overheating the oil. Heat makes the oil darker and may reduce its nutritional value (as if a substance that is essentially liquid fat can be said to have nutritional value).

Manufacturers using the expeller press are concerned primarily with pressure, not temperature. Essentially the raw material for the oil is forced into smaller and smaller spaces as it moves along the press. The tight squeeze increases the amount of oil extracted from the plant, at the cost of raising the temperature. It’s not uncommon for the temperature of the expeller press to rise above the 120 degree F limit imposed on the cold-press method.

After pressing is complete, manufacturers of coconut, palm, grapeseed, and rice bran oils often use a chemical solvent to extract even more oil from the plant. And as you might expect, extracting oils with a solvent requires manufacturers to do some additional work to then remove that solvent from the resulting oil.

Finally, the oil is refined to remove color, odor, and bitterness before being packaged for sale.

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About Shala Howell

Writer of things ranging from optical network switching white papers to genetic testing patient education materials to historical fiction set in an 1880s asylum. When I’m not scratching my head over pesky characters who refuse to do things how I want them done or dreaming of my next book (which will of course be much easier to write than the current one), my writerly self can be found blogging about life with a very curious Ten-Year-Old at Caterpickles.com, or musing about books and the writing life at BostonWriters.wordpress.com.
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