PRACTICAL HINTS ON PASTEURISATION

New Zealand Times, Volume LXXI, Issue 4313, 23 March 1901, Page 3 (Supplement)

PRACTICAL HINTS ON PASTEURISATION

(By J. A.Kinsella, Dairy Commissioner.) Thai word '‘pasteurisation” originated from the name of Louis Pasteur. It -was Pasteur who first studied the world of bacteria in a systematic manner. He proved that fermentations in beer, wine and milk are due to living organisms, and that the different species of bacteria are acted on by different ferments. At temperatures above 160 degrees bacteria -do not grow well. Very tew thrive above 125 degrees, and the higher the temperature is raised the more bacteria perish. Heating milk to boiling point or thereabouts always imparts a boiled flavour; but it is possible to reduce this so as to be almost imperceptible oy heating to only 158 degrees. Experiments have proved that if milk or cream is kept at 158 degrees for ten minutes most of the bacteria will be killed. Cream may be heated to 165 degrees, if quickly cooled afterwards, without developing a belied flavour. Some spelcies of bacteria are not destroyed even by heating the milk to 212 degrees or 215 degrees. That being so, it seems useless, to attempt to overcome the prejudice against the so-called I boiled or cooked flavour, when a sure safeguard against the most common dangers can be secured by heating to between 158 degress and 165 degrees. In other words, the worst flavour producing germs .are destroyed at the latter temperatures. It has been proved that raising the tempdraturo of the cream rapidly to 158 degrees and keeping it at this point for two to five minutes, then,' immediately chilling it to 65 degrees, or below, will destroy nearly all forms of bacterial life. But although heating to 158 degrees, or even boiling point, kills most of the bacteria, it does not destroy their spores; hence, if the milk or cream is held at a favourable temperature —between 80 degrees and 100 degrees—for,any length of time, these spores will develop and the battle- begin anew. The cooling sheu'd be done rapidly, especially between 120 degrees and 65 degrees. _ ■ The percentage of fat leift in the skimmilk should not exceed one-half of onetenth of one per cent. (0.05). Samples of the skim-milk should frequently le tested with tha Babcock. The sample should be composed of small quantities taken from the outflow of the separator at different times. A very accurate method is to have a small hole in the skimxnilk spout, by'ifhich an occasional drop is obtained ima tin; from which the sample is afterwards taken. The question is, should wp pasteurise? To this it may be replied that the system of pasteurisation has passed beyond the experimental stage. My opinion is that we should pasteurise. Milk ,as it comes from a health v cowfed on pure food is absolutely pur© an 1 sterile, and if it can be so secured in a sterilised, air-tight bottle it will keep for an indefinite period. ; From a practical butter and cheese-making standpoint, it is utterly impossible to secure milk atthe factory in a sterile condition. Millions of germs (bacteria) are floating in the air, in. the dust of the roads, and la the water, and are contained in the dirt that adheres to the cow’s udder - and flanks, and to the hands and clothing of the milker. It must not, however, be supposed that all germs are undesirable, some of them being very useful in the manufacture of butter and cheese It is true that pasteurisation will u-t improve the flavour of first-class milk < r cream, also that taints imparted by onions, turnips, rape,'etc.; it very strong iu the milk, cannot bo’wholly remove'!. It 1 is‘also true that a large number of the factories ; are not properly equipped for successfully carrying put the work of pasteurisation-, but I think the time has arrived when they should he equipped, f.r.d that w© should take up the question and have it properly and scientifically carr el out in all factories. In visiting last- year a largo number of factories throughout the colony I found that a large number of them could be equipped for carrying on pasteurisation at 1 a very small c( sr.. From a butter-making standpoint, the cream only need be pasteurised. In the spring and summer, however, when the milk is fed to calves, it pays to heat the akim-milk to 160 degrees. _ This process increases its keeping qualities, and makes it a much better food for calves. The whole milk may also he pasteurised. Reports show that in Denmark it is compulsory to pasteurise all the milk, in order to prevent tuberculosis from spreading through the medium of the skim-milk. I would, however, recommend pasteurising the cream only, and if it is found necessary to pasteurise skinn-milk this may be done more ‘ewoipmically by using the exhaust steam' frWm the engine; By means of an insulated skim-milk tank covered over, and passing the exhaust steam direct into the skim-milk;, it may he scalded with little or no cost to the average factory, where the exhaust steam is at present allowed to go up in the air. Although, as before stated, pasteurisation is far beyond, the experimental stage, thelre is yet a diversity of opinion as to whether pasteurised cream gives a better" butter than non-pastourisod. It is a fact that pasteurisation-has a tendency to destroy the fine aroma of the raw butter, but while! there-is one factor against it, there are many in its favour—viz. : (1) Pasteurisation gives a mild, uniform flavour to the butter; (2) it gives an increased keeping quality to she butter; (3) it destroys the injurious bacteria in milk or cream ; (4) it improves thel flavour of milk tainted hv „ strongflavoured food; and (5) it reduces, the germ-content of. the milk, which means that it leaves a cleaner seed-bed for the lactic-acid germ, which is introduced .into the cream through the! medium of a pure-flavoured fermentation-starter —an. indispensable factor in the manufacture of a uniform article of butter.

On the whole, seeing the difficulty there is in obtaining a good quality of clean-favoured milk, even at our best factories, pasteurisation is sure to be beneficial in bringing about uniformity in our butter. The Danes hav'e universally, adopted the system of pasteurisation and-ripehing with pure cultures, and their enviablcJ position in the British markets is sufficient proof that these methods have brought about uniformity in their butter. I venture to say that similar results can be brought about in this colony if pasteurisation is carried cut generally and systematically. It is said that Danish butter does not possess good keeping qualities. It is true that some brands of Danish butter, made from sweet cream for special cus-tomers-to catch a particular trade at Home, do hot keep long when exposed on the counter; but it is also a feet that butter made in Denmark from pasteurised cream with pure cultures has been shipped to great Britain, afterwards reshipped to this colony, and then found 10 he in excellent condition. The cask of butter I refer to was received last season and examined by my predecessor, several other, experts; and myself at the Moturoa grading store, and s was pronounced almost faultless. The Department is "now prepared to assist any factory: wishing to introduce pasteurisation by sanding_ an inspector to give the necessary advice and assistance in regard tc the proper equipment and the setting up of the plant, and in the hest methods of pasteurisation and craam ripehihg. -

| The subject may be summed up in- the | following points: 1. Pasteurising means heating the milk or cream to between 155 degrees and 160 degrees and keeping it at that point from 15 to 30 minutes, then cooling quickly down to 65 degrees, or a suitable ripening temperature. 2. Heating alone is not pasteurising, but the'term is also used when milk or cream is heated and immediately cooled, which is sufficient to destroy a large number of the .bad-flavour-producing germs in cream ■which is to be ripened. - 3.’ The effectiveness of pasteurisation is in proportion to the height of tempera'ture,' and'the length of time the milk or cream is exposed thereto. 4. The sooner the milk is pasteurised after being drawn from the cow the greater the value of the process, for the fewer germs will there be to kill. : : 5. The best results are obtained by tha quickest heating with the least sporching of the milk or cream, which moans that it must bo kept in constant motion. 6. If you are not prepared to properly equip your factory and get sufficient assistance to carry out the work systematically and well, do not pasteurise. 7. If you are not prepared to thorougaly clean your coolers, heaters, and everything connected with the cream, do not pasteurise. • • 8. If cans, pails, vats, pasteurising machines, and all utensils are not thoroughly washed and sterilised, pasteurisating is of but little avail. 9. Always remember that pasteurisation is not a cure-all for cvciry kind of tainted and dirty milk. , 10. If you do not intend to ripen your cream, and you are not familiar with tho method of preparing a good fermentation starter, do not pasteurise. 11. Lastly, if you are not thoroughly posted in the proper methods of past'aurisatiou, and wish’to undertake the work,' ask some person who is so'posted s to visit yotir factory for consultation.