Most factories like to have a well supply, if only for economic reasons, and some food factories are in isolated country places and have to rely on well supplies. The use of river water for cooling is very common, but local authorities may prohibit the use of well water or river water for purposes in which direct contact with foods may be possible.
In one way, the sanitary quality of water is more important in food factories than for domestic supplies because pathogens do not proliferate in clean water but many do so rapidly in foods and watery residues.
Contaminated water in a dairy naturally contaminates everything with which it comes into contact. Considerable losses have occurred through failure to realize this elementary fact. The use of an assumed "pure" water supply to wash and rinse down equipment may easily lead to the introduction of fault producing organisms, and leave the equipment in a worse condition than before.
A simple method for testing the sterility of equipment is to pass a known volume of sterile water or water of known bacterial content through it and determine the increase in microflora. Much general information on the control of dairy water supplies is available.51»52»148
2. Milk
The effect of contaminated farm water supplies on the keeping quality of milk has been recognized for a long time. With unhygienic methods and no cooling the coli-aerogenes group usually causes the most damage. If the milk is refrigerated, Pseudomonas and similar types may produce unclean flavours, bitterness and sometimes stinking milk. Clean methods without cooling can give good milk, but dirty methods and cooling can easily lead to the above faults.
Ropy milk is a classical example of a fault due to contaminated water.
Many examples are given in the literature,51» 1(>4»839 and common causes are Aerobacter and Alcaligenes. Ropiness in pasteurized milk was found840 to be caused by M. viscosus, and the reservoir of infection was found to be the
washed cans coming into the dairy from low-lying districts. It was found that about 1 % of producer-retailers' milks suffered from ropiness,841 the peak being from July to September. Outbreaks in pasteurized milk were due to the producers' milks, and the ropy organisms were derived from the farm water supplies.
Organisms producing faults in milk and dairy products are often spread by water residues in cans which travel backwards and forwards between creameries and farms. A common fault in hot weather is malty flavour, and it has been shown that chlorination of the water used for washing the utensils will largely reduce if not eliminate the fault.
Water contamination may have special significance when samples of milk, etc. are taken for official purposes and held under refrigeration until tested.
Thus it was found842 that milks from a certain area failed to pass the methy-lene-blue test when held overnight at 4°C, a temperature that is generally considered to hold micro-organisms in a static condition. These samples were found to give almost a pure culture of Pseudomonas which grew at 4°C sufficiently to reduce méthylène blue. All the samples concerned came from farms using well water which contained this particular type of Pseudomonas, and which was used by the farmers to wash out their cans.
The general question of the suitability of farm water supplies for dairy purposes has been comprehensively reviewed.843
3. Bottle Washing
About eleven thousand million bottles of milk are delivered annually in the U.K. When the product is sterilized in the bottle or jar, the hygienic condition of the container is not a matter of great importance, but when it is not, as with pasteurized milk, the micro-organisms remaining in the bottle can easily invalidate the efficiency of the pasteurizing and handling methods.
In the bottle-washer, hot detergent solution at 60-63°C cleans and sterilizes the bottles, which are then treated by a warm recirculating rinse, a cold rinse and a final mains rinse. The warm recirculating rinse is the key point in the system; it may easily have the bacteriological quality of sewage because ideal conditions exist for the growth of bacteria. The subsequent rinses will then not be sufficient to deliver a bottle of good hygienic quality. A standard of not more than 1000 per ml for warm recirculating rinses is reasonable and, provided that the cold and final main rinses are virtually sterile, good bottles can be obtained. Chlorination of the rinses and the use of a bactericidal detergent are satisfactory solutions to this problem.
The development of aseptic filling techniques will naturally require a completely sterile water for the rinse sections unless the product is filled hot and the container heat-sterilized immediately before filling. There are general reviews of bottle washing.si, si2
168 4. Cream
Bitterness in sterilized cream may be caused by the growth of Proteus, the contamination being derived from the cooling water and some cans being "leakers".
5. Butter
Of all dairy products, this is the one most vulnerable to spoilage by water bacteria. The most dangerous are those that are strongly lipolytic, proteo-lytic and grow at low temperature. The most important genus is Pseudomonas, and this is able to grow in water. Serious incidents may occur even when a water supply that is satisfactory from the public health point of view is in use.
The organism most frequently concerned is Ps.fluorescens and the commonest defects are surface taint, putrid butter, cheesiness and "rabbito", and these defects can nearly always be traced to the water supply.844-7 Butter is susceptible because it is always washed and so comes into direct contact with the water. The evidence usually leaves little room for doubt.
The damaging effect of water bacteria depends not only on the types and numbers present, but also on the type of butter. A well-made salted butter will be more stable microbiologically than a badly made unsalted butter.
There appears to be a minimum contaminating dosage necessary to initiate growth and taint production. In general, the higher the count of the water, the greater the adverse effect on the butter.
6. Cheese
This product is less liable than butter to spoilage by water bacteria for two reasons : (a) it is acid and therefore not a favourable medium for water types, and (b) apart from the washed curd types it does not come into direct contact with water as butter does.
Further factors are the high salt content in the aqueous phase (about 6%), the anaerobic conditions inside the cheese, and the antagonism of a numerous and vigorous lactic flora. Probably the most important types for cheese are the coli-aerogenes group and the yeasts and moulds because they can resist acid conditions. These types are often found in farm supplies.848»849
The unripened types such as Cottage cheese are much more susceptible to water organisms than the drier, more acid types such as Cheddar.850
Nevertheless, these bacteria are capable of causing rancidity in Cheddar cheese, and they may also produce discoloration in cheese when potassium nitrate is added to suppress gas formation by coliforms. In an investigation of spoilage in Cottage cheese,850 it was found that there was heavy contamin-ation in the wash water, and that the count of the curd increased consider-ably after washing; several water supplies contained large numbers of lipolytic and proteolytic bacteria but few coli. Psychrophilic bacteria in the
water used for washing Cottage cheese have been found to cause defects, and pasteurizing the water for twenty seconds at 85°C,851 and thorough cleansing of the equipment lead to better quality cheese.
H. Effluent
The problems of economic production, quality of products, consumption of water and quality of effluent in a dairy or creamery and closely inter-related. The B.O.D. of an effluent is a useful measure of wastage and efficiency of processing. For a manufacturing creamery an effluent or water con-sumption to milk ratio of three is a satisfactory figure. The ratio is usually slightly higher, but depends on the nature of the manufacture. Cheese and condensed milk make the highest demands. Control methods are described in the literature.51,52, we, 852,853
27. PUBLIC HEALTH ASPECTS A. General
The medical officer and health inspector, and the dairy technologist look at dairy products from different points of view. The former are concerned solely with public health aspects, i.e. the presence of injurious bacteria, whereas the latter are concerned chiefly with palatability, appearance and keeping quality. The former may have little knowledge of the technology and the latter little realization of the health hazards involved. Consequently, the medical officer may place a rather academic interpretation on everyday bacteriological phenomena, and the technologist not concern himself with health aspects as he should.
The disease aspect of micro-organisms in dairy products, especially raw milk and its products, was formerly a problem of considerable importance,854 but the almost universal heat-treatment of milk permits only an occasional outbreak of such diseases, and then only from raw milk, inadequately heat-treated milk or recontaminated dairy products. There have never been any legal tests or standards for pathogens in dairy products. Tuberculosis legislation refers only to the animals. It would be very expensive to test milk supplies routinely for pathogens. Comprehensive reviews of milk-borne disease have been given.34-36