Milk quality and saving energy can work hand-in-hand
With input costs on the rise around the country, dairy producers are looking for ways to reduce their overhead. One often overlooked, but costly nonetheless, is energy costs. According to a study of dairy farms in New York state published in 2003, dairy farms use between 800 and 1,200 kilowatt hours per cow per year with some operations as high as 1,736 kWh. This study also reported that 46 percent of all electrical use was for milk harvesting, specifically milk cooling, vacuum pump, and heating water.
One of the best pieces of equipment producers can purchase to save on energy usage is a refrigeration heat recovery unit which captures reject heat from a farm's refrigeration system and uses it to preheat water. "When properly installed, a heat recovery unit can reduce a farm's hot water costs by 50 percent," explains Scott Sanford, a senior outreach specialist with University of Wisconsin-Madison. This system, which consists of simply a water tank surrounded by a heat exchanger, can heat water to 100 to 120 degrees F before it enters the hot water tank.
Hot water is one of the prime demands on farms, and lack of it can reduce the effectiveness of detergents for cleaning pipelines and tanks. If pipelines, tanks, or other milking equipment are cleaned with water that is not hot enough, detergent solutions are less effective at disinfecting hard to clean places which will lead to an increase in a dairy's standard plate count.
Another critical part of producing high quality milk is cooling. Once it leaves the cow's udder at 101 degrees, milk must be cooled as quickly as possible for storage at 45 degrees or less as per requirements of the Pasteurized Milk Ordinance. A temperature of 38 to 40 degrees is desirable to slow bacterial growth. Milk that is improperly cooled or not cooled quickly enough will damage product quality and may produce an off-taste.
Milk cooling is also a process that requires high levels of energy. As milk moves from the cow's udder to storage in the bulk tank, a great deal of heat needs to be removed. This creates a high demand on the bulk tank compressors which on some farms will run for hours after milking is completed. The Pasteurized Milk Ordinance requires that milk be cooled to 45 degrees or less within two hours of the end of milking. If a farm is not meeting these requirements during the heat of the summer, it won't have enough cooling capacity.
One solution to cool milk more quickly and to reduce energy demands by compressors is the installation of a precooler. Typically added between the milk receiver jar and the bulk tank, a precooler uses well water as a coolant to lower milk temperature close to the ground water temperature. In the Upper Midwest and Northeast, milk can be cooled to around 55 degrees. Rapid cooling through the use of a plate cooler will also reduce the growth of contaminating bacteria. Better yet, this has the potential to reduce milk cooling costs by 60 percent through reduction of the demand on compressors.
"This equipment works by transferring the heat from the milk across a stainless steel plate into the well water which is flowing in opposite directions," Sanford explains. "A precooler works very well in parts of the country that have low ground water temperatures but will not be as effective in warmer climates."
Compressor efficiency can also be improved to reduce energy expenditures. Sanford recommends scroll compression which is 15 to 20 percent more efficient than a traditional reciprocation compressor. Producers purchasing a new bulk tank should ask their supplier about scroll compression. Additionally, for those who have a bulk tank and experience a refrigeration system failure, scroll compressors can replace existing equipment for an additional investment of about $300 to $500.
Sanford advises producers to not overlook energy costs, even though they only represent about 2 percent of milk production costs. For producers with less than 100 cows, a heat recovery unit is likely to be a more cost effective investment because it takes less energy to cool milk than it does to heat water. "Keep in mind that precoolers and heat recovery units are competing technologies," Sanford reminds. "Be sure to evaluate your system to ensure that both pieces of equipment will be cost effective. In many cases, a heat recovery unit alone may provide the best return on investment."
Barbano, D., Y. Ma, M. Santos. 2006. Influence of Raw Milk Quality on Fluid Milk Shelf Life. J. Dairy Sci. 89 (E. Suppl.): E15-E19
Sanford, S. 2008. Wisconsin Energy Efficiency and Renewable Energy Resource. 5 Nov. 2008
Ludington, D. and E. Johnson. 2003. Dairy Farm Energy Audit Summary Report. New York State Research and Development Authority. Available at
United States Food and Drug Administration. Grade "A" Pasteurized Milk Ordinance, 2007 Revision.
Source: NMC National Mastitis Council