Lesson 3. GRADING AND QUALITY OF RAW MILK FOR CONDENSED MILKS
GRADING AND QUALITY OF RAW MILK FOR CONDENSED MILKS
Milk and milk products are a rich and convenient source of nutrients for people in many countries and international trade of milk-based commodities is significant. All foods have the potential to cause food borne illness, and milk and milk products are no exception. Dairy animals may carry human pathogens. Such pathogens present in milk may increase the risk of causing food borne illness. Moreover, the milking procedure, subsequent cooling and the storage of milk carry the risks of further contamination from man or the environment or growth of inherent pathogens. Further, the composition of many milk products makes them good media for the outgrowth of pathogenic micro-organisms. Potential also exists for the contamination of milk with residues of veterinary drugs, pesticides and other chemical contaminants. Therefore, implementing the proper hygienic control of milk and milk products throughout the production, processing, and handling operations is essential to ensure the safety and suitability of these foods for their intended use as milk and milk products form a large portion of the diet of consumers especially infants, children, and pregnant and lactating women.
3.2 Good Quality Milk and Milk Products
For better understanding of the quality of milk and milk products and their grading, it is necessary to know the real meaning of fresh, good quality milk and milk products. The following few terms help to understand it better:
1. Milk is the normal mammary secretion of milking animals obtained from one or more milkings without either addition to it or extraction from it, intended for consumption as liquid milk or for further processing.
2. Milk product is a product obtained by any processing of milk, which may contain food additives, and other ingredients functionally necessary for the processing.
3. Composite milk product is a product of which the milk, milk products or milk constituents are an essential part in terms of quantity in the final product, as consumed provided that the constituents not derived from milk are not intended to take the place in part or in whole of any milk constituent.
4. A reconstituted milk product is a product resulting from the addition of water to the dried or concentrated form of the product in the amount necessary to re-establish the appropriate water to solids ratio.
5. A recombined milk product is a product resulting from the combining of milk fat and milk-solids-non-fat in their preserved forms with or without the addition of water to achieve the appropriate milk product composition.
Several chemical and physical properties of milk follow from its composition and structure. These properties can affect the processing of milk and the quality of milk products.
Conservation of milk solids in form of dried milks has shown an increasing trend in the recent decades owing to the extended shelf life and cost benefits in packaging, transportation and storage of such products. Availability of such products has also facilitated to overcome seasonal and regional deficiency of fluid milk.
In course of manufacture of condensed and dried milks, the quality of raw milk, the pretreatments employed and the drying variables used determine, to a great extent, the physical, chemical, microbiological and organoleptic characteristics as well as the shelf life of the finished product. The importance of raw milk quality in relation to manufacture of concentrated and dried milks is innumerable.
The quality of raw milk to be used should be judged with respect to the following criteria
- Relationship of milk quality with finished product quality.
- The influence of milk quality on product yield and the process efficiency.
- The quality criteria appropriate for today’s technology.
- Requirement of separate quality criteria for each end use, if any.
- The terms specified by the manufacturer of concentrated and dried milks for milk quality.
Raw milk is extremely variable in its composition and characteristics. The quality of raw milk arriving at the dairy premises is of vital concern more so today than ever before, largely because milk, the raw material, now constitutes something like 60-70 % of the final product cost. It is therefore vitally important that
- The quality is high, so that wastages are minimized.
- Processing speeds optimized and
- Product quality raised.
The poor quality milk is not readily accepted by manufacturers for conversion to products. Milk which is unsuitable for the liquid market is certainly unsuitable for manufacture of condensed milks and milk powders as quality specifications are becoming more stringent and manufacturer of the products is required to produce “tailor made” products for specific end uses.
Quality of raw milk used for manufacture of condensed milks and milk powders has the following significance:
1. It decides the ease with which it can be handled during processing and manufacture.
2. It influences the processing parameters and their effects on powder characteristics.
3. It influences quality specifications of the finished product.
4. It affects the functional and physico-chemical properties of the finished product.
3.3 High Quality Milk
The quality of the raw milk is the single most important criterion that determines the quality of the end product. The quality of the raw incoming milk in turn is dependent on the sanitary procedures followed during the milk production and transportation.
Healthy cows, milk produced under clean environment, clean and hygienic utensils, freedom from colostrum, prompt cooling of milk soon after milking and transport under refrigerated state are the factors that determine the number of microorganisms.
The received milk is thoroughly checked for organoleptic qualities like colour, odour, taste (raw milk is seldom tasted at the entry point) etc. along with other platform tests like clot on boiling (COB), alcohol / ethanol test to determine the suitability of milk for heat processing.
When producing condensed milks / powder for commercial use it must comply with certain bacteriological, chemical, and physical standards. Obviously the quality of the final product is a function of the raw milk quality. It is therefore vital for a profitable production to have milk of first class.
The following criteria are used to define high quality raw milk:
1. It has a normal taste and appearance.
2. It has a normal chemical and physical composition.
3. It does not contain harmful chemical contaminants or residues.
4. It has a low total count of bacteria and somatic cells.
The ideal milk for the dairy industry is one which is rich in constituents, which is drawn from the udder of a healthy animal, to which no non-milk constituents have been added and in which no changes have taken place.
The compiled quality criteria, their suggested and/or desirable limits and their relevance to product quality are depicted in Table 3.1.
3.3.1 Raw skim milk / Raw whole milk
The milk should be fresh and stored at maximum 5ºC for maximum 48 hours after milking, and should not have had any pretreatment other than
- Separation of cream / desludging by means of a centrifuge.
- One heat treatment at max. 72ºC and 15 s.
- Standardization of fat content by separation of cream and or addition of skim milk.
The following Table 3.2 shows reasons for rejection of skim milk powder for not meeting the quality specifications. It is evident from the tabulated values that the total acidity of raw milk and its bacteriological quality can affect the powder.
3.3.2 Sweet whey
When the whey is stored between the cheese factory and the evaporation process at a temperature exceeding 10ºC, then the storage time should not exceed one hour. If the storage temperature is below 10ºC, then the storage time should not exceed ten hours.