Opportunities to Improve Milk Quality.

Many opportunities exist to improve the bacterial quality of milk, particularly of manufacturing-grade milk. Test results, using plate counting procedures by 10 Iowa dairy laboratories, reflect a gradual improvement in recent years in manufacturing-grade milk quality. In recent months, 70 to 84% of 3,000 to 5,000 individual Iowa farm's manufacturing-grade milk samples tested each month were placed in Class I (plate-loop count of less than 500,000/ml). Problems still exist in farm milking equipment sanitation, undersized bulk tanks with inadequate cooling capacities, and delays in processing raw milk. USDA DMCC results on milk samples obtained from milk-storage tanks in Iowa dairy manufacturing plants reveal that in 1977-78 only 5.8 to 13.1% of the commingled raw milk would be classified as Class I. These results reflected a deterioration in bacterial quality of raw milk from the time milk leaves the farm until held in the plant storage system. Part of the quality deterioration can be blamed on failure to empty and clean plant storage tanks often, allowing too much time before milk is processed, and on milk not at 40 F or less. Cheese and butter exhibits reveal that poor milk quality has a negative influence on product flavor quality. Quality assurance programs for dairy farms, milk transportation, and plant storage must stress sanitation, cold temperatures and minimum times before processing to obtain good bacteriological quality milk and pleasing-flavored dairy foods.

The 3M Automatic Colony Counter in the Bacterial Evaluation of Manufacturing-Grade Milk.

Twenty-seven raw milk samples were analyzed for their bacterial quality by the Standard Plate Count (SPC) and the plate loop count (PLC). All resultant plates were counted by three different technicians either manually or with a 3M Brand Automatic Colony Counter, Model 630. Results emphasize the superiority of the SPC over the PLC for samples with high bacterial numbers. The automatic colony counter tended to underestimate the number of colonies on a plate. Correction factors for conversion of PLC counts to SPC and automatic to manual counts were calculated. It is recommended that the PLC and the automatic colony counter be used with appropriate correction factors for routine analysis of large numbers of samples.