In its normal state, milk fat forms a stable emulsion with water of the oil-in-water variety. To stabilize the emulsion, the fat is enveloped in an adsorptive covering of phospholipids and proteins.
The break-down of this emulsion and separation of all non-milk-fat components is the aim of AMF production. It is possible to break down the membrane by means of mechanical energy or a chemical reaction. Mechanical energy (e.g. homogenization) is used to break open the membranes. Smaller fat globules are formed by the newly created membranes, which themselves were created by the fragmentation of the original membranes and from the proteins in the milk serum.
Reduction of the fat globules is also employed, for example, in the processing of drinking milk, in order to prevent the so-called “creaming” effect.
Complete phase inversion is not possible with this process. Furthermore, a relatively stable emulsion layer is formed from the existing amount of cream and part of the serum; this impedes separation as a third layer between the oil and serum phases.
Special measures are necessary if the reversible process of formation of new, intact fat globules is to be minimized.
The following applies for minimizing the emulsion content: the three fractions, namely fat, phospholipids and proteins, are largely responsible for a stable emulsion. If one of the three fractions is removed, or is changed to such an extent that it can no longer be used as a building block for the membranes, then the formation of intact fat globules is prevented and the formation of emulsion is not possible.
When all the above-mentioned parameters are applied to phase inversion, they result in a degree of inversion of 80 – 95 percent.
Unlike standard homogenization, the aim is not to reduce the size of the fat globules but to destroy the membranes or envelopes so that the fat can be recovered. It is therefore important to prevent the formation of fat globules with intact new membranes.
An initial conclusion from the above is that the amount of serum should be minimized before the start of actual production of the oil, so as to minimize the amount of available membrane building blocks.
In order therefore to achieve adequate release of fat, a cream fat content of greater than 75 percent is required which is realized in the cream concentrator. The release of the fat, and the phase inversion brought about by this, take place by mechanical fragmentation of the intact fat globules in a homogenizer.