Corn oil is generally made using a combination of natural and chemical processes that ultimately separate the oil in the germ of the corn from the rest of the plant materials. You can make your own corn oil at home if you must, but it will not be the most efficient way to make use of your corn crops. Making corn oil may take some experimentation before you discover the way that works best for you.
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Remove the corn kernels from the cobb. You can do this by cutting them off with the paring knife, just as if you were removing them from the cobb so that a child may eat them more easily. As you remove the kernels, let them fall into the large tub. If you are going to start with a small batch of corn oil, then use a bucket instead of a tub.
Steep the corn kernels in warm, distilled water for 40 hours. You should not use hot water, but you do want to keep the water relatively warm so if your climate is such that the water will cool overnight, you may need to refresh the water periodically.
Strain the corn kernels out of the distilled water. They should have started to "loosen" at this point, and you will clearly see the tiny germ at the center of each kernel surrounded by a layer of white, starchy material. You will need to use your hands to pull the light yellow germ out of the kernel. You will only use the germ for corn oil. At this point, it will be clear to you how much corn you need to make a very little corn oil. As you separate the germs, you can drop them in the screw press.
Press the corn germs with the screw press. As you press the germs, they will lose water and other liquids, including corn oil. Let these liquids fall into the bowl, where they will separate from each other, with the corn oil floating on top.
Use the spoon to skim the corn oil off the top of the liquid in the bowl. You can use this liquid for cooking, or you can store it in an airtight container to use at a later date. You can dispose of the water that remains in the bowl.
Nearly any other form of vegetable oil is more efficient to make at home than corn oil. This can be a fun experiment, but it is generally more efficient if you are doing this for money or energy saving purposes to work with other sources of oil, such as olives.