Sunflowers have been harvested for thousands of years. Sunflower oil is one of the products created by harvesting sunflowers. The extraction of sunflower oil is done through exposing the seeds to extreme pressure. Before the extraction can occur, the seeds must undergo preparation. After the extraction has taken place, the oil can be refined further and then continues through various finishing processes.
Sunflower seeds raised for oilseed have all trace metal and extraneous material removed before continuing into the press. This includes removal of the hull and skin. The clean seeds are then ground into meal that creates more surface area to extract oil from. Rollers and hammer mills are used to crush the meal to the correct consistency for the presses. The meal is heated to aid in the oil extraction. Any impurities remaining from the cleaning are removed prior to pressing.
The seed meal moves into an expeller press to squeeze out the oil. The process is called cold-pressing. The meal undergoes increased pressure from the press as it moves through the machinery. After pressing, the meal has hexane added to it to chemically extract any remaining oil. Hexane is not used by every sunflower oil producer; smaller mills and natural oil producers skip the chemical extraction process.
Refining the oil from sunflower seeds can use either a natural or chemical method. Naturally refined oil uses citric acid and is cooked at 250 degrees F; chemical refining involves the use of phosphoric acid and raises the temperature to 500 degrees F. The refining process is used to reduce the smoke point of the oil and therefore lets the oil be cooked at higher temperatures. Sunflower oil can be refined twice to lengthen the shelf life up to four years. Not all sunflower oil is refined; unrefined sunflower oil has a shelf life of only one year. As the refining process continues, the oil evaporates and the steam is collected. The oil remaining is boiled to release the hexane, which is also recycled. Refining produces a colorless, odorless liquid.
The extracted oil is then split into one of two finishing processes. Oil being processed for cooking is bleached with fuller's earth and activated carbon to absorb pigmented material. Oil being processed for refrigeration is rapidly chilled and filtered to remove remnant waxes to ensure the oil doesn't solidify. The oil is then placed into a vacuum and reheated at a range of 440 to 485 degrees F. Steam is then passed over the oil to deodorize it removing any bad taste or smell left from the distillation process. The finished oil is then measured using an IV into plastic or glass bottles.
The seed meal left behind by the extraction process is considered a byproduct. This meal is pressed into seed cake for animal feed and low-grade fertilizer.