Advisory Microbiological Standards and Tolerances for Raw Milk

Abstract

To study the value of recent modifications of microbiological teflts used for advisory purposes, samples of tuberculin tested milk, taken at weekly intervals over a 5 year period from the Trawscoed Experimental Husbandry Farm and selected a t random during a 12 months period from farms in Wales, were examined by a temperature compensated keeping quality test at 2 2 O , colony count on Yeastrel milk agar in 3 days at 30' and coli-asrogenes colony count on violet red bile agar in 20-24 hr at 30".The results show that milk produced and handled under hygienic conditions can be expected to have colony counts of less than 2x104/ml and coli-mrogenes colony counts less than lO/ml when examined within 18 hr of milking.OVER THE past 30 years several workers in England have studied bacteriological tests suitable for use in advisory work for evaluating methods of milk production. Notable among them has been the work of Mattick (1930), Wilson et al. (1935), Clegg, Wohlgemuth, Crossley & Andrews (1949) and Clegg (1955).More recently Leech, Egdell & Thomas (1956) have described an investigation on a random sample of farms in England and Wales of methods of milk production, in conjunction with bacteriological and keeping quality tests of the milk. A statistical analysis of the results showed that of the many factors in milk production technique investigated, only the sterilization of utensils and the cooling of the milk showed any correlation with the keeping quality.The time is opportune to review the microbiological standards and tolerances used for advisory purposes, having regard to the changes in bacteriological techniques recently introduced in England and Wales. Among these has been the change of incubation temperature from 37" to 30" for the colony count and coli-aerogenes test and the use of a temperature-compensated keeping quality test by clot-onboiling (COB) at 22".The work reported in this paper was undertaken with a view to studying the value of these tests and t o suggest satisfactory levels related to the keeping quality of the milk. There is comparatively little information about the relationship of the colony count and coli-aerogenes test a t 30" to the keeping quality of farm milk supplies. METHODS Control milk samples from the Experimental Husbandry FarmBacteriological results for TT milk produced under good conditions were obtained with 78-24 hr old samples from the first 10 gal of milk over the equipment a t the

The Microflora of Raw Milk as Determined by Plating on Yeastrel‐milk Agar Incubated at 30°

“…The distribution of milk samples in relation to the range of colony count ( Table 1) is representative of the kind of results obtained during advisory work. Farm milk supplies giving colony counts of <2x104/ml a t 30" are considered t o have been produced and handled under satisfactory conditions (Griffiths, Druce 6 Thomas, 1957), and counts t5xlO3 are not uncommon where the milking equipment is efficiently cleansed. When the colony counts range from 2 x lo4 to 2 x lo6 it is generally recognized that cleansing methods could be improved, whereas oounts of >2 x lo5 are termed unsatisfactory.…”