Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.10 Food industry 937
Figure 14.10.2. Flow diagram of edible oil processing.
Dehulling: After cleaning, it may be necessary to remove the seed’s outer seed- coat
(hull). The seedcoat contains little or no oil, so its inclusion makes the extraction less efficient.
Also, the next processing step is grinding to reduce particle size, and any tough seedcoats
would interfere with this process. If the hulls are not removed prior to extraction, they
will reduce the total yield of oil by absorbing and retaining oil in the press cake. An acceptable
level of hull removal must be determined, depending on the desired protein level of the
final meal. Hulls are removed by aspirator and undehulled seeds are removed from the kernels
by screening and returned to the huller. Some meats still adhere to the hulls, which are
beaten, then screened again to obtain the meat.
Grinding, rolling, or flaking: After dehulling, the meats are reduced in size, or
“flaked,” to facilitate oil removal. Proper moisture content of the seeds is essential for flaking,
and if the moisture level is too low, the seeds are “conditioned,” with water or steam, to
raise the moisture to about 11%. For solvent extraction, flakes are commonly not less than
0.203-0.254 mm (0.008-0.010 inch), which can be solvent extracted efficiently with less
than 1% residual oil. Thinner flakes tend to disintegrate during the solvent extraction process
and reduce the miscella percolation rate.
Cooking: Prior to extraction, the flakes are heated. The purpose of cooking the flakes
is: (1) cell walls are broken down, allowing the oil to escape; (2) oil viscosity is reduced; (3)
moisture content is controlled; (4) protein is coagulated; (5) enzymes are inactivated and
microorganisms are killed; and (6) certain phosphatides are fixed in the cake, which helps to
minimize subsequent refining losses. Flakes are cooked in stack cookers to over 87.8 o C
(190 o F) in the upper kettle. Flakes with high phosphatide content may benefit from being
cooked at slightly lower temperatures to avoid elevating refining losses. The temperature of
the flakes is raised to 110-132.2 o C (230-270 o F) in the lower kettles. The seeds are cooked