Cold-pressed oil is made from many foods, but on a small scale it is most often from seeds and nuts. This form of expressing oil from foods does not involve the use of chemicals. Instead, the oils are extracted by way of pressing on the food item at a temperature below 48.9 degrees Celsius, within an expeller press. An expeller press is a screw-type machine that puts pressure on the food item and oil seeps out. This process allows the oil to hold onto subtle flavours that are otherwise lost at higher temperatures. The cold-pressed oil process can be achieved at home with a motorised or hand-crank expeller press.
Clean the food item you plan from which you will cold-press the oil. Remove any coating or husks left on the seeds or nuts.
Check over your cleaned product for a second look. It is important there is no seed or nut chaff, sand, dirt or other debris. Any of these items left in the mix can absorb precious oil, cause extra wear on the press or even damage press parts.
Test the moisture of the seeds or nuts. Different food items require a different moisture percentage. Use a moisture tester to determine the wetness content. Sunflower seeds require no higher than an 8.5 per cent moisture content, while safflower seeds can have up to an 11 per cent moisture content, for example.
Heat the seeds or nuts right before you are ready to press. Heating helps the extraction of the oil. Set your oven no higher than 48.9 degrees Celsius. Place the seeds on a baking tray and heat them for about 10 minutes.
Feed the seeds or nuts into the press. If you have a motorised press, turn it on first. If you have a crank-style press, start cranking as you feed in the seeds or nuts.
Remove the press's end cap when you have finished with your seed or nut stock, or if the machine becomes full. Allow all the oil to drip through the holes of the end cap, before removing it to take out the press cake. This is the ground up seed or nut meal.
Clarify the cold-pressed oil. Cover the container of oil, with a piece of cheesecloth, and allow it to rest for three to four days in a dark or semi-dark location. Any debris in the oil will float to the top. Remove the top layer of the oil.
Heat the oil no higher than 48.9 degrees Celsius to remove any additional debris if the oil appears cloudy. This will evaporate any leftover water and extinguish any leftover bacteria. Use a cooking thermometer for this process.
Store your cold-pressed oil in an airtight container, away from light.
There are fanning mills and spiral separators available for removing seed and nut debris if you are cold-pressing oil on a larger scale. Although some instructions say you can heat your seeds or nuts up to 71.1 degrees Celsius, seeds heated above 48.9 degrees Celsius are not considered cold-pressed oil.