During the past 20 years the manufacture of recombined milk has developed considerably, particularly in Southeast Asia, India and Latin America.
Recombination offers a number of advantages for countries where milk produuction is insufficient, in that transport and handling costs are considerably reduced and raw material storage costs are low. Moreover, this method encourages the development of a local dairy industry and also the creation of packing centres. However, certain problems are involved, mainly a decrease in the organoleptic quality of the recombined product. Many countries recombine milk from skimmed milk powder and anhydrous milk fat (AMF). The recombined milk can be mixed in turn with local raw milk. In both cases the product meets a certain amount of consumer resistance because of the poor taste (Hardy, 1980; Ramet, 1978 and 1980).
The normal flavour of raw milk cannot be easily defined in specific terms. It is characterized by a bland odour and taste resulting from the complex mixture of various constituents under different physical conditions.
The fact that its organoleptic characteristics are not very marked is due to the following:
no constituent is present in sufficient concentration to produce a dominant flavour;
inhibiting effects lessen the specific taste of some constituents. These are the sodium chloride-lactose antagonism; the buffer effect of lactoproteins and fats vis-à-vis water-soluble and fat-soluble constituents;
the main constituents of milk in its natural state are not volatile, which accounts for its characteristic slightly pronounced odour.
Defects in milk flavour generally appear when the concentration of one constituent varies considerably compared to its usual average content. Absence of any defect usually distinguishes a product of good organoleptic quality.
In the case of raw milk these variations in composition can have different causes. They can be due to the animal's physiology as in the case of so-called abnormal milks, or to variations resulting from chemical, physical or microbial transformation of milk components. These are the most frequent defects. Defects can also be due to the presence of transmitted external flavours for which milk merely acts as a vector.
All these defects can be found in recombined milk since the milk raw materials used can be affected by the above-mentioned factors. Moreover, the heat treatment used for the production of skimmed milk powder causes a change in the natural taste of milk and even the appearance of abnormal tastes.
Two physico-chemical criteria can be used to classify powder qualities, i.e. the solubility value and the insoluble protein level (King, 1966).
Anhydrous milk fat can also show quality differences due on the one hand to the raw material and, on the other, to the preservation process and length of storage. Two main chemical values are commonly used to establish the quality of this fat, i.e. peroxide value and acid value.
Recommendations on the quality of milk powders and fats intended for the manufacture of recombined milk products have been described in a document of the International Dairy Federation (IDF, 1978).
In the first part of this publication the mechanisms of the main adverse effects are examined, in particular the interactions between their development and the technological treatment undergone by the milk constituents from collection to their utilization for recombining.
The second part discusses the influence of raw material quality on the taste of consumer milk and of the proportion of recombined/raw milk that can be used without causing changes in taste.
The third part of the IDF document assembles the specifications and methods of analysis of raw materials that can be used for preparation of reconstituted milk.
