Cooking oil is refined to become a food product.
Many different kinds of vegetables contain oils. When pressed, the oil will be crude. To use vegetable oil for food or fuel, it has to be refined, but the refining process varies depending on whether the vegetable oil will be used for food or fuel. Food refining aims at purifying the oil so that it can be eaten, while fuel refining aims at breaking the oil down into a form which can be used in engines, stoves, or heaters. Add this to my Recipe Box.
Instructions
Preparing the Oil
1. Clean the feedstock (the plant matter you will use to produce the vegetable oil). Foreign particles such as sand and dirt should be removed mechanically (shaking over a sieve) and by washing with water.
2. Dry the feedstock. The feedstock should be as dry as possible, otherwise the pressing will release moisture with the oil, making it cloudy and harder to process.
3. Remove any shells or peels. This is normally done mechanically in a sieve or using suction (which works like a big vacuum cleaner and removes the lighter shells from the heavier seeds).
4. Grind the feedstock to a pulp using a mill or grinding stone. Many oil presses integrate grinding and so can receive the feedstock directly from the previous step. If separate grinding is needed, feed the pulp into the oil press, either manually or by conveyor, depending on the amount of pulp to be processed.
5. Separate the extracted oil from the pulp. This is done mechanically; most oil presses have different outlets for the extracted oil and the used pulp. Filter the oil through a sieve or paper filter to clarify it.
Refining Cooking Oil
6. Treat the oil with an alkali solution to neutralize the free fatty acids and phosphatides. Centrifuge the oil to remove any particles, phosphatides, proteins, and other contaminants.
7. Wash the oil with water to remove any residual soap. Soap in the oil is caused by saponification of small amounts of triglycerides in the oil.
8. Bleach the oil to remove substances with color, such as carotenoids and chlorophyll. The process uses adsorbents such as acid-activated clays, which are a type of clay that will absorb ions when initially treated with acid. The clay is placed in a filter through which the oil passes. This removes the colored substances from the plants, leaving the oil with its natural color only.
9. Remove volatile components. Most oils contain various smelly substances which will evaporate when heated. This is normally done by deodorization, which injects steam under a high vacuum and temperature. If this is not done, the oil will smell raw and crude.
10. Filter and store the oil until it is time to be used.
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