Anhydrous Milkfat ("butter oil")
Anhydrous milk fat, butter oil, can be manufactured from either butter or from cream. For the manufacture from butter, non-salted butter from sweet cream is normally used, and the process works better if the butter is at least a few weeks old. Melted butter is passed through a centrifuge, to concentrate the fat to 99.5% of greater. This oil is heated again to 90-95oC and vacuum cooled before packaging.
The processes for the production of anhydrous fat, using cream as the raw material, are based on the emulsion splitting principle. In brief, the processes consist of the cream first being concentrated to 75% fat or greater, in two stages. In both of these stages, the fat is concentrated in a hermetic solids-ejecting separator. The fat globules are then broken down mechanically, so that phase inversion occurs and the fat is liberated. This forms a continuous fat phase containing dispersed water droplets, which can be separated from the fat phase by centrifugation. This is similar to the concentration method for buttermaking, with the addition of the mechanical rupture of the emulsion and additional separator for removal of the residual water phase.
One of the key machines in the system is the mechanical device for phase inversion. This can be in the form of a centrifugal separator equipped with a serrated disc. The disc breaks down the emulsion, so that the liquid leaving the machine is a continuous oil phase, with dispersed water droplets and buttermilk. Larger equipment could be equipped with a motor-driven serrated disc or with a homogenizer. After phase inversion, the fat is concentrated to 99.5% or greater in a hermetic separator.
Fractionation of anhydrous milk fat
Milk fat is a complicated mixture of triglycerides that contain numerous fatty acids of varying carbon chain lengths and degrees of saturation. The proportions of the various fatty acids present will also vary depending on the conditions surrounding the production of milk.
One method of milkfat fraction is by thermal treatment. The mixture can be separated into fractions on the basis of their melting point. The technique consists of melting the entire quantity of fat and then cooling it down to a predetermined temperature. The triglycerides with the higher melting point will then crystallize and settle out.
In the modern thermal fractionation method, sedimentation by gravity is replaced by centrifugal separation. Since a modern separator generates a force that is thousands of times greater than the force of gravity and since the sedimentation distances are very short, the process is incomparably faster. The crystallizing stage can also be accelerated, since the crystals need not be large if centrifugal separation is employed.
Fractionation of milkfat can also be accomplished by supercritical fluid extraction techniques.
Some of this material has been condensed from the Alfa-Laval Dairy Handbook, with permission.