10-05-2014, 03:28 PM
FIXED OILS & FATS
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SEQUENCE OF OPERATIONS
The sequence of operations in processing oil seed for pressing is as follows:
1. STORAGE
The seeds, nuts, or plant tissue containing the oil must be properly stored and prepared for extraction, to maintain high quality in the final product.
If the oil-bearing material is dry, it must be stored so that it remains dry, for optimum extraction and quality of the oil. If the oil-bearing material is wet plant tissue, it should be processed for oil-extraction as soon as possible after harvest so that storage time is kept to a minimum. Oils in the presence of water deteriorate rapidly, forming free fatty acids and rancid off-flavors.
2. CLEANING
After the oil-bearing materials have been removed from storage, the first step in preparing them for oil extraction is to clean them.
The cleaning is done so that the oil is not contaminated with foreign materials.
3. DEHUSKING/DEHULLING
After raw material has been cleaned, it may be necessary to remove its outer seed coat.
The seed coat does not contain oil, so including it makes extraction less efficient. Also, the next step will be grinding to reduce particle size, and any tough seed coats interfere with this process.
Some seeds, such as peanuts, can be shelled by hand. Some others, such as sunflower seeds, are usually hulled in machines.
4. GRINDING OR ROLLING
Seed is not usually pressed whole, since oil extraction is more efficient if the seed is in smaller particles.
Grinding the oilseed is one effective way to reduce particle size.
A hand-operated mortar, millstone grinder, or even a kitchen meat grinder can be used to convert the seeds to a coarse meal. Small hammer mills, motor or hand-powered, are also used.
5. HEATING
A final step in raw material preparation is heating the ground or flaked oil seed.
Heating is useful in deactivating enzymes in the plant tissue that have a deteriorating effect on the oil quality.
If the oil seedcake (that is, the residue remaining after oil removal by pressing) is to be used for feed or food, heating may be useful in increasing protein availability.
Sometimes oil-bearing material is pressed without being heated. Oil extracted in this way is called cold press oil.
6. PRESSING
The materials prepared in these ways are pressed, usually in a lever press, hydraulic press, or expeller, to remove the oil.
7. REFINING
Cold press oil can be of such high quality as to need no refining if it comes from seeds that are fresh and of good quality.
All other oils especially those which have been pressed from lower quality feedstock is likely to have some undesirable cloudiness, color, or flavor that needs to be removed.
i. Removal of Cloudiness
Pressed oils need to be filtered to remove particles from the pressing operation, if the oil is to be clear and clean.
ii. Removal of Excess Color
For the removal of excess color, bleaching earths are effective. The oil is heated and mixed with 1-2 percent of its weight of an effective bleaching earth purchased from a reliable supplier forthis purpose. After a contact time of approximately one hour,the bleaching earth is separated by filtration. Activated carbon can also be used.