Evaporated milk composition

Fig. B-2. Percentages of the RDAs for infants which am supplied by 1 qt (0.9 liter) of either human milk or evaporated milk diluted 1 1 with water. (Based upon data from Recommendea Dietary Allowances, 10th rev. ed., National Academy of Sciences, 1 989, and Table F-21, Food Compositions, p. 450 of this book)...

Clarification by removal of casein with such agents as calcium chloride, acetic acid, cooper sulfate, or rennin has often been employed to obtain a serum more suitable for refractometric measurements. Obviously the composition, and hence the refractive index, of such sera will depend on the method of preparation. Furthermore, some of the serum proteins may be precipitated with the casein by some of the agents used, particularly if the milk has been heated. Refractive index measurements of such sera are not generally considered as satisfactory as freezing point measurements for detection of added water (David and MacDonald 1953 Munchberg and Narbutas 1937 Schuler 1938 Tell-mann 1933 Vleeschauwer and Waeyenberge 1941). Menefee and Overman (1939) reported a close relation between total solids in evaporated and condensed products and the refractive index of serum prepared therefrom by the copper sulfate method. Of course, a different proportionality constant would hold for each type of product. 

Fluid milk is commonly subjected to a combination steam injection/in-fusion and vacuum flash evaporation process to remove volatile off-flavor compounds. The process is designed to remove the same amount of water by the flash treatment as is added during steam injection/infu-sion, so that the composition of the milk remains unchanged. This treatment is most effective for removing volatile, water-soluble flavor compounds, such as those from weeds and feed consumed by the cow. The additional heat from this process usually provides further improvement in product shelf life. 

Another possibility for the modification of fat composition and physical properties (e.g., milk fat) is the application of molecnlar distillation. This method involves the evaporation of more volatile molecnles and their condensation. After the process of milk fat distillation, fractions rich in short- and long-chain TGA and with rednced amounts of cholesterol are obtained. These fractions are used for the production of dietetic butter for people suffering from disturbances in fat assimilation (Staniewski, 2000). 

The performance of reverse osmosis in concentrating milk is limited by the osmotic pressure and most commercial modules have operating pressure limits of 30 to 40 bars, which limits the concentration of milk to a factor of three to four. In the production of skimmed or whole milk powder, the milk is usually concentrated to 45 to 50% total solids before spray drying. Thus reverse osmosis cannot substitute entirely for conventional evaporation, rather it is used as a pre-concentration step before evaporation, to reduce operating costs or to increase capacity of existing plant. The relative energy consumption of reverse osmosis and thermal concentration methods in the concentration of milk differ by an order of magnitude, and with thin film composite membranes the cost of reverse osmosis is lower still. 

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