Milk temperatures in 35 ice-bank and 23 direct-expansion (58 total) farm bulk milk tanks of atmospheric design were measured during the summers of 1958 and 1960. Additional information was obtained by a questionnaire.
Cooling requirements specified in 3-A Sanitary Standards were used as the basis for determining performance. Twenty-two percent of the DE tanks failed during the first milking to properly cool the milk to 40°F, and 26% failed during the second milking. IB tanks had 34% fail for the first milking and 17% for the second milking.
For the second milking 35% of the DE tanks permitted the milk to exceed a 50°F blend temperature. The average time above 50°F was 45 minutes. IB tanks had 23% fail to meet this requirement for an average time of 20 minutes. About 75% of the producers poured milk into the tanks in quantities of 3 to 5 gallons. Average milk temperature rise was 11 °F for both types of tanks.
Maximum stratification temperatures for the DE tanks averaged 2.6°F and for the IB tank 3.2°F. The stratification temperature patterns were different for the two types of tanks.
Some of the faulty tanks were rechecked in 1960. Mechanical and refrigeration problems along with operator neglect were responsible for most of the tanks not cooling to 40°F in the specified time.
When loadings are heavy and air temperatures are high, second-milking blend temperatures will exceed 50°F in many farm tanks as they are now designed and operated. Faster rates of milking will also tend to cause high blend temperatures.
A systematic routine check of all tanks would reduce considerably the numbers not meeting 3-A Standards. An inspection system should involve the hauler, fieldman, sanitarian, tank dealer, and the producer.
1Presented at the 47th Annual Meeting of the International Association of Milk and Food Sanitarians, Inc., Oct. 26–29, 1960 at Chicago, Illinois.
2Journal Paper J-3997, Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa; Project 1282.