HEALTH NOTES

Evening Post, Volume CXII, Issue 152, 24 December 1926, Page 13

HEALTH NOTES

CLEAN MILK

PRINCIPLES UNDERLYING ITS PRODUCTION

DUTY OF DAIRY FARMERS,

(Contributed by tho Department of

Health.)

This article is written more particularly for the information and guidance of dairy farmers in country districts to achiove their aim to turn out milk as clean, and free from contamination as they can,.

Milk is ono of the most nourishing and most delicato of all foods—nourishing becauso it supplies all tho constituents necessary to support life, and delicate because it is prono to undergo deleterious changes if due precautions aro not observed in its handling. Theso changes are chiefly induced by germs or bacteria, and as cleanliness, is the main factor by which the number and species of such germs may be kept under control, cleanliness in the handling of milk is of tho utmost importance. Except that first drawn from the teat, milk as it exists in tho udder of tho healthy cow may be considered to be practically frea from germ life, and with proper precautions sterile milk may bo drawn from tho udder of a healthy cow, but in ordinary practice, anilk is more or less exposed to bacterial contamination, and this is the reason souring and other changes take place. By far the greater number of bacteria in milk come from ordinary dirt, and may be kept out of tho milk by cleanly methods of producing aud handling milk. Milk is ono of the best media used in the laboratory for growing bacteria, and the few bacteria that aro found in 'even the best of milk may therefore multiply to millions and may make the milk unwholesome unless groat care is taken to prevent their growth and increase. PBODITCTION OF CLEAN MILK. The cow must be healthy; the shed must bo clean, well lighted and ventilated, and the surroundings also should be cleau. Any operation likely to produce dust before or during milking, especially of hand milking, must be avoided. The cow must bo clean and washing tho -udder and flanks with water gives tho best results —after washing the udder and teats must be wiped with a clean damp cloth. The milkers' hands and clothes must be clean. In hand-milking, tho milk pail should have as small an opening as can be used. The first stream of milk from each teat should bo rejected, and the practice of wet-handed milking should be avoided. Tho milk should be removed from tho cowshed immediately after milking for straining and cooling. It should be handled in a clean, airy, well-lighted shed kept solely for the purpose. The milk niust be cooled to 50 deg. F. where possible, otherwise to the lowest temperature obtainable. It should be kept as cool as possible in closed vessels during storage and transit. The milking utensils, including the cooler, should be well rinsed with cold water immediately 4iftcr iise and: after rinsing, the utensils should bo thoroughly washed and scrubbed with hot water to which soda has been added, . and afterwards rinsed in clean water and sterilised by steam.

Sterilisation depends entirely on heating the utensils to a sufficiently high temperature* for a sufficient period of time. Scalding will not sterilise. After sterilisation the utensils must be protected from contamination until required. Straining cloths and udder cloths and everything that, comes either directly or indirectly in contact with the milk must be washed and sterilised after each milking. WHEN STRAINING SHOULD BE DONE. Straining should take place before cooling, which should be done as coon as possible after milking and invariably in a pure atmosphere. The value of a straining cloth is frequently overrated. The straining- cloth strains out visible dirt to a considerable extent, such as particles of grit, straw, etc., from the mi)k, but bacteria are far too small for any straining cloth to prevent them from passing through. It is therefore useless for the purpose of removing bacteria that havo already gained access to the milk. ■ If a cloth is used that has net been properly washed and sterilised since it was last used, bacteria will have bred and multiplied on the-cloth, and it will thu.i be a fertilo source of contamination. Where there is any risk of the straining cloth not being properly sterilised after each milking it is better to aso a cotton wool disc. These discs ■ aye cheap enough, and after use can be thrown away. The quantity of ..10

dirt strained out of tho milk is visible on the strainer, and is an excellent guide as to the quality of the work 'being dono in the cowsheds. Butter1 muslin is not an efficient strainer, even when several thicknesses aro used. A straining cloth is far more effective, and this has to bo washed and thoroughly sterilised by boiling or in steam and new ones frequently used, otherwise bad results will be obtained. The -metal gauze strainer keeps out tbe grosser impurities, and requires the same care as tho above. Do not ai-, tempt to strain too largo an amount of milk without changing the strahu.r or straining material. If this is done the latter part of tho milk poured on it may have tho effect of washing through dirt with bacteria, v.-hich has been strained out of tho previous m:lk. The strainer may be a means of :.nffeling a. large quantity of good milk by a small amount of bad milk. COOLING PROCESS.

It is almost impossible to prodnsc milk freo from bacteria or to destroy all bacteria by pasteurisation. It is therefore necessary to prevent bacteria from multiplying in milk, and the only allowable method of presrving milk ia by cooling it. A low temperature restrains the growth of all kinds of bacteria. The degree of temperature needed to preserve milk will depend greatly on. the length of time that tho milk is to be kept. The marked cft'ecta of temperature are well recognised, and overyone is aware that milk keeps better in winter than in summer. The

higher tho temperaturo tho more readily do coliform bacteria multiply, and these bacteria readily cause souring and curdling of milk.

Milk to bo safely kept should be cooled immediately after milking to 50 degrees Fahrenheit or lower, and with tho exception of tho necessary heating for pasteurisation should not subsequently be permitted to exceed that temperature. Tho maintenance of a low temperature alone will not ensure a low bacterial content unless tho milk is clean to start with, but on the other hand maintenance at a comparatively high temperature, such as GO to 70 deg. Fahrenheit, is likely to result in a high count even with an originally "clean" milk. During a part of the winter months there may bo little difficulty to cool to 50 deg. Fahrenheit, but in summer months this temperaturo in many cases, especially in the North Island, is only possible with tho uso of ice. Observations in Auckland have shown that for six months of the summer tho average temperaturo on delivery of raw milk was 70 dog. Fahrenheit, and for six months 57 dog. Fahrenheit. Where the water supply is derived from a deep well the difficulty is less. If a demand for ice could be established, possibly tho cost of production of ico might bo lowered and its use encouraged, especially at farms within easy access of a city.

If tho temperaturo of the milk is lowered sufficiently at the farm, the temperature of tho outer air docs not affect it markedly during transit except when it is exposed to the direct sun's rays or in an excessively warm atmosphere. Milkcans are frequently left by farmers at the side of the road to await collection by the depot wagons and are frequently exposed to the direct rays of the sun and to dust. This is frequently the case also at railway stations. Covered motor wagons are fortunately superseding open carts, and by this means .transport to the cities is accelerated.

In retailers' premises in tho towns there should be no difficulty in imposing a definite standard of 50 deg. F., at which tho temperature of all milk for sale should be kept. In houses the use of tho ice chest for storage of milk should be more general. It is important for the public to recognise it has a duty also in the matter of storing tho milk in thoroughly clean receptacles and keep it stored at a low temperature, and protected from flies, dust, and odours. MILK COOLERS. Milk coolers offer a largo surface for the contamination of tho milk. If the cooling is carried out in a proper daily where the air is pure tho number of organisms gaining admission is small, but in cases where cooling is carried out in a dirty cowshed or in dusty places serious pollution has to be considered. On the other hand coolers are frequently found in a dented or damaged condition, which makes it practically impossible to keep them clean. Many havo repeatedly been repaired with solder, and it is seldom that a smooth surface has been left. It is advised that coolers bo fitted with metal covers: these covers lit one on each sido of the cooler and,protect the milk from dust while in. use. They are easily removed for cleansing, and they do not interfere with the cleansing of the cooler itself.

In regard to cooling on large scale, where certain types of pasteurisers are used, milk can bo left in the pasteuriser, nftor having been heated to the requisite temperature for the required time, and cooled by passing the cooling mixture through the coil. This means less handling and also prevents exposuro of the milk to large surfaces or to the air, and is a great improvement in this respect on the use of the ordinary surface coolers. MIXING MILK. It seeiM hardly necrs r-»ry to point out tin) injurious effecta of the addition of stale liiillc to fresh milk, but fresh -milk is oft^n spoiled in this way. Th:; mixing deems' where a milkman mixes the remjunts of his morning delivery with the Irish milk received by him. in th'j afternoon or tho fo.'lowing day. TII.O consequence is an immediate increase in the number of: -oactcria and a considerable reduction < f the pori'.v! 'luring w.''..\';i tho mill: imams useful Apart from this, in !'><•• 'minato mixni;-; of various grades of rjiik at uiiik depots, etc., results ?.t. comparatively cU'an milks being do;r ivlatcd by dirty ones. N.B. —Other aspects of this subject will bo dealt with in a future artitle.