Degumming
- passing hot water through the oil to precipitate out gums and
proteins that are soluble in oil but not in water, then discarding the
water along with the impurities
Neutralization or Deacidification - treats the oil with sodium hydroxide or sodium carbonate to pull out free fatty acids, phospholipids, pigments, and waxes
Bleaching
- removes off color components by treatment with fuller's earth,
activated carbon, or activated clays, followed by heating, filtering,
then drying to recoup the oil
Dewaxing or Winterizing - improves clarity of oils intended for refrigeration by dropping them to low temperatures and removing any solids that form.
Deodorizing - treating with high-heat pressurized steam to evaporate less stable compounds that might cause "unusual" odors or tastes.
Filtering
- a non-chemical process which screens out larger particles, could be
considered a step in refinement, although it doesn't alter the state of
the oil.