The Effects of Rancid Milk on Cheddar Cheese

One of the most serious defects .of fluid milk is hydrolytic rancidity. Although not a new problem, recent practices in the dairy industry have increased its incidence. On the farm, the use of pipeline milking and transferring systems, in conjunction with bulk cooling and storage, involves excessive agitation and foaming of the raw milk. Both agitation and foaming enhance the development of rancidity. Additional agitation occurs when milk is pumped into storage silos, and pumped about the plant f or processing. Dairy processing facilities are becoming more centralized. Hence, raw milk must be transported longer distances to the dairy plants. Also 9 milk is often collected from the farm on alternate days. This results in longer time intervals between milking and processing, hence there is more time for rancidity to develop. Consequently, milk is frequently near to having rancid flavor by the time it reaches the dairy plant (77). The rapidly growing cheese industry in the United States now utilizes a quarter of the nation\u27s milk supply (53). Over 1.8 billion kg of cheese were sold in 1980, which is a 53% increase from 10 years earlier (53). Per capita sales of American cheese (primarily cheddar) rose from 3.1 kg to 4.1 kg in the same 10 year period (53). Since both cheddar cheese production and the incidence of rancid milk is increasing, it must be concluded that increasing amounts of cheddar cheese are being manufactured from rancid milk. This raises the questions of how great is the frequency and what are the types of defects in cheddar cheese due to rancid milk. Deleterious results may include flavor and body defects, lowered yields, and undesired compositional changes. The objectives of this study were to determine the effects of milk rancidity on the yields, composition, curing, and organoleptic quality of cheddar cheese manufactured from rancid milk. Since these factor s are involved in the per unit cost of making the product, as well as affecting acceptability of cheese by consumers, an additional objective was to provide managers in the cheese industry with information concerning necessity of a higher quality milk supply. The managers can then make proper decisions to assure better quality, such as education of patrons, drivers, and plant workers, and the use of penalties or premiums in payment based on the degree of rancidity in farm milk