SCIENCE BULLETIN, No. 20. 



Some ten years ago the Alstonville Co operative Dairy Company had 

 trouble with the quality of the butter then being manufactured, and an 

 officer of the Dairy Branch investigated the matter and successfully used 

 atmospherically exposed plates to trace the origin of the infection causing 

 the deterioration, thereby enabling the company to remedy the matter. 

 Knowing the value of arriving at and locating causes of deterioration by 

 means of bacteriology, a scheme was worked out early last year whereby- 

 whatever came in contact with the dairy produce after its arrival at the 

 factory until it was placed on the market, could be systematically examined 

 and the results compared. The general adoption by the New South Wales 

 dairy companies of the practice of pasteurising cream made the initiation of 

 such investigations the more opportune. The object aimed at was twofold : 



(a) To demonstrate the efficiency of pasteurisation as carried out* at 



certain factories. 



(b) To demonstrate whether or not the product was recontaminated 



after pasteurisation, and if so, how the infection took place. 

 The methods followed were very similar in all cases and were carried 

 .out as follows : 



1. Samples were taken of the cream on arrival at the factory, after blending in 



bulk. 



2. The same lot of cream, after being neutralised and pasteurised by either the 



"flash" or the "holding" system as it came from the outlet pipe of the 

 " flash " or (in the case of the holding system) direct from the tank, was aigain 

 sampled. In both cases these samples were obtained before the cooling process 

 commenced. 



3. In the case of the flash pasteurisation, the plates were exposed 2 minutes, and' 

 in one case (Example 1) five minutes to the air over the pipe cooler used first 

 to reduce the temperature of the cream. 



4. Plates were atmospherically exposed for tifteen minutes over the cream-receiving 



and neutralising vat in the case of Example 1 to demonstrate the extent of 

 infection from the water spray tower ; in other cases this was not done. 



5. Where vats were used for holding cream (after passing over pipe coolers) pending 



churning, the tops of such vats being open, another series of plates were 

 exposed to the atmosphere for 2 minutes in one case (Example 2) and five 

 minutes in another (Example 1). 



6. The same cream was again sampled as it came from the holding vats to enter 



the churns. 



7. A sample was taken of the water used for cleansing and rinsing the churns and! 



utensils. 



8. A sample was taken of the water used to bring butter to the breaking point andi 



thereafter used to wash the butter. 



9. A sample was taken of the butter made from the aforementioned cream as it 



came from the churn . 



10 Plates were generally atmospherically exposed in the churn room 2^ minutes, 



but in one case (Example 1) for five minutes, in all cases where the butter (or 



cream as it gravitated along the fluming from vat to churn) was exposed to the 



air. 



11. A sample of the surface of the butter was taken from a box when packed and 



ready to be lidded. 



In conjunction with making these bacteriological examinations, the 

 produce was graded for quality at all stages, thus : 



(a) Cream on arrival at factory. 



(b) Cream after treatment when ready to churn. 



(c) Butter soon after being manufactured. 



