The Care of Milk and Cream for Manufacturing Purposes

New Zealand Journal of Agriculture, Volume 81, Issue 4, 16 October 1950, Page 369

The Care of Milk and Cream for Manufacturing Purposes

By

R. W. NAYLOR,

Farm Dairy Instructor,

Department of Agriculture, Te Awamutu.

OF the many tasks associated with the efficient management of a farm dairy and the production of a raw material of the finest quality for manufacturing purposes none can be considered of greater importance or more likely to influence the attainment of such a standard than the care or attention milk or cream receives while held at the farm dairy awaiting transport to the factory or manufacturing centre. THE work involved in keeping a milking shed and its immediate surroundings in a sanitary condition and maintaining a milking plant and separator equipment in a similar state may be faithfully carried out, resulting in the production of milk, or cream of high quality at the time of its release in the farm dairy, but if adequate attention and scrupulous care are not exercised in maintaining that condition, what was originally a high-grade product deteriorates speedily. Because milk and cream are complex organic substances subject to natural decomposition, even under ideal conditions, it is obvious that the introduction and subsequent development of undesirable bacteria or the absorption of unclean flavours from whatever source must have a detrimental effect on the keeping quality and final grading of the product. Holding Product under Hygienic Conditions There must be facilities for holding milk or cream at the farm dairy under the most hygienic conditions. The cream or milk stand or compartment should be well ventilated and only pure air should enter it. A standard of cleanliness which will prevent the possibility of contamination by the absorption of foreign odours from an external source or as a result of unclean conditions under which the milk or cream is held should be maintained. A milking shed should be planned so that the milk stand or separator room is on the windward end, and the immediate surroundings should be laid out to prevent the traffic of stock in the vicinity of the milk stand or separator room. Such an arrangement, particularly if the area is well grassed, makes contamination from an external source unlikely, and where home separation is done it would be

quite safe to have a louvred safe or compartment built out from the separator room for the overnight storage of cream. The common practice of holding cream in the separator room is dangerous, chiefly because taints may be absorbed from milk-splashed and sour-smelling concrete, fermented areas of skimmed milk resulting from any leakage in its disposal, or from stored goods and old clothing, all of which have characteristic odours capable of absorption by milk or cream. Too much care therefore cannot be taken to make sure that where milk or cream is held on the farm unsatisfactory conditions do not arise, and this can be brought about only by a high standard of cleanliness constantly maintained. Cooling of Milk and Cream To appreciate fully the value of cooling and its effect in maintaining the quality of milk or cream (and in many cases where feed flavours and other physical taints are encountered in improving the quality) the composition of milk or cream and the effect which a rapid lowering of temperature has on the bacteria content must be considered. Under normal conditions bacteria are the main cause of deterioration in both milk and cream. Milk and cream, if not subjected to rigid temperature control, provide ideal conditions for the growth of bacteria of many and varied types. This results in rapid decomposition of the organic matter on which the bacteria feed and a corresponding decline in quality. An efficient safeguard is a cooler capable of reducing milk or cream rapidly to a temperature of at least 65 degrees F.; where the cooling water is drawn direct from its source even lower readings can be obtained. At such temperatures the growth of bacteria is checked, any decline in quality arrested immediately, and the value of efficient cooling clearly demonstrated in the production of milk or cream capable of retaining its original flavour and sweetness. Clean Containers No greater or more prolific source of contamination can be found than a can or lid which as a result of persistently hurried and imperfect cleansing has a surface on which the residues of previous consignments are all too apparent,

either in the form of a yellow fat deposit or a whitish encrustation of dned-on milk deposit. Both are fertile media for the development of putrefactive bacteria and, particularly if the can is porous or rusty from lack of tinning, for the more immediate tainting of its contents by the absorption of the unclean flavour which a metal surface in such a condition cannot fail to impart. It is only after thorough cleansing, by scrubbing with hot water and by using a suitable . detergent to remove fat or milk deposits, and final sterilis-

ing with plain boiling water that cans may be considered fit receptacles for the storage or conveyance of milk dr cream. One of several suitable deterg—caustic soda, plain washing soda, or some proven commercial preparation—may be chosen, but if high quality is the aim, scrubbing of the container on every occasion before use cannot be neglected. Frequent Stirring or Plunging The importance of frequent stirring or plunging as a means of maintaining the keeping quality of milk and

cream is not recognised as widely as it should be, if the obviously unused plungers not infrequently seen in farm dairies may be accepted as evidence. There have been many cases where neglected plungers when put to proper use have been responsible for effecting an immediate improvement in quality and the resultant grading of milk and cream. Plunging assures even distribution of fats throughout the mass of milk or cream treated. It disturbs and exposes to the atmosphere the milk serum which, because of its composition, is the principal source of bacterial development, whether of useful or harmful, natural or putrefactive bacteria. By retarding bacterial growth plunging helps to prolong the period for which the product will remain pure and sweet. The accumulation of gases in milk and cream which are associated with seasonal growth of pasture or a result of infection by certain types of bacteria is set free by vigorous plunging, and the possibility of taint reduced considerably. Mixing Warm and Cold Milk or Cream The mixing of warm and cold milk or cream cannot be condemned too strongly. It provides more favourable conditions for bacteria growth in the combined product and impairs its keeping quality. If milk or cream must be mixed, it is essential that both samples should have been cooled to similar temperatures and thoroughly stirred and plunged before they are mixed. Protection at Roadside By no means least in importance in ensuring that milk or cream is of good quality is the provision of adequate shelter for the product when delivery is taken at the roadside, where it may remain, according to circumstances, for from a few minutes to an hour or more before being picked up and transported to the factory. Any ill effects resulting from variations in the time milk or cream is on the roadside can be overcome by providing a stand which gives ample ventilation but complete protection from the rays of the sun. When cans are unprotected and become heated by the sun’s action the quality of milk or cream is immediately harmed by contact with the heated metal, and if exposure is sufficiently prolonged, the partial cooking of the fats takes place, resulting in rancidity and the off flavour which such treatment promotes. The practice of placing a sack over cream cans on an exposed platform or bank by no means can be termed adequate protection. Even if the surface of the can is completely covered the general rise in temperature of its contents is extremely harmful, and the covering may easily be blown aside, leaving the can unprotected. It is therefore only by the construction of a suitable stand that dangers can be guarded against and the standard of quality of milk or cream maintained in the final stages of its production.