During the 20th century, milking dairy cows with machines replaced hand milking, saving time and labor. Although bucket milkers were used before World War I, their widespread use followed the Rural Electrification expansion in the 1930s. Through the 1940s and 1950s most milk cans were replaced by refrigerated bulk milk tanks, and tank trucks for every-other-day pick up became common. Dumping bucket milkers into milk transfer systems saved manual strain when carrying milk, and around-the-stable milking pipelines became common with larger milking barns. The advent of elevated milking parlors reduced stooping and squatting for the operator. Developments with chemical cleaners, as well as water heaters, insured effective and automatic cleaning-in-place of milk handling equipment.
Automatic cluster removers and in-place cleaning of milking units in all types of parlors have become more popular. Concentrate feeding in parlors has generally been replaced by computerized feeding systems and total mixed rations (TMR). Automatic recording of milk yields, coupled to electronic identification of cows, is increasing. Criteria for properly designed Automatic Milking Systems (Robotic milkers) were added to the Grade “A” Pasteurized Milk Ordinance (PMO) in 2003 and these systems are available for use in the U.S.
Basic to the operation of milking machines is a partial vacuum or “negative” pressure between one-third and one-half atmosphere. This pressure differential moves milk away from the cow’s teats, or fluids away from any opening, since air rushes in to equalize pressure. A continuous vacuum stresses teats, so pulsing air collapses the teat cup liners (inflations) and massages the teats. Milk flows directly away from each teat, preventing flooding or cross contamination among quarters. Shaking or agitating milk leads to possible foaming and increased rancidity. Milk should flow gently through the milk lines and not be mixed with the air. However, pulsing air and fluids create turbulent and fast moving slugs of rinsing, washing and sanitizing solutions used to effectively clean the milking systems.
Milk is an ideal medium for the growth of bacteria. In the early 20th century, several outbreaks of human illness were caused by pathogens in milk. Because of these outbreaks the production, pasteurization and other processing of milk and dairy products became a public health concern. Regulations, inspections and enforcement of strict standards have since effectively minimized pathogens in milk, and ensured a safe, high quality pasteurized milk supply throughout the United States.
This is an excerpt from the Dairy Practices Council’s Guideline #4, Installation, Cleaning and Sanitizing of Large Parlor Milking Systems. More information can be found at: http://www.dairypc.org/catalog/guidelines/all-guideline-listing/installa....

Steve Lehman is the Technical Area Supervisor for Michigan Milk Producers Association (MMPA), a milk marketing cooperative serving over 1,200 farms located in Michigan, Indiana, Ohio, and Wisconsin. Steve has over 25 years’ experience working with MMPA in the areas of farm inspection, milk quality, equipment evaluation, and facility design. He is currently serving as the Task Force V Director for the Dairy Practices Council, and resides in Ithaca, Michigan.