As debate on the merits of mandatory pasteurization of milk intended for cheesemaking continues, global demand for raw-milk cheese is increasing.
While the Food and Drug Administration is conducting a scientific evaluation on the microbiological safety of cheeses made from raw milk, such as Parmigiano Reggiano, Gruyere, Gouda, and Cheddar, it may be useful to review some of the risk assessments and policy discussions that are occurring around the globe.
United States regulations governing the use of raw milk for cheese-making, promulgated in 1949, require cheesemakers to either pasteurize raw milk or hold cheese at no lower than 35°F for a minimum of 60 days. Mycobacterium tuberculosis and Brucella abortus were the pathogens of concern at that time, and aging allowed pathogen inactivation.
As a result of improvements in animal health and disease management, these are no longer primary pathogens of concern. However, Escherichia coli O157:H7, Salmonella typhimurium DT 104, and Listeria monocytogenes are. Of particular concern to FDA are studies documenting survival of E. coli O157:H7 in aged Cheddar cheese (Reitsma and Henning, 1996).
A review of all cheese-associated foodborne disease outbreaks reported during 1973– 92 (Altekruse et al., 1998) noted that cheeses are an infrequent source of outbreaks and that none were associated with raw-milk cheese aged for 60 days.
Ripened soft cheeses such as Camembert, Brie, and Queso Fresco present a higher risk than hard cheeses because the former’s higher pH and moisture content promote the growth of microbial pathogens. U.S. regulations permit manufacture of semisoft and soft-ripened cheeses from raw milk, provided that these cheeses are aged for 60 days at 35°F or above. Pathogens such as L. monocytogenes can grow to high levels during 60 days of aging, so safety must be achieved through use of other control strategies.
A 1996 Canadian government proposal for mandatory pasteurization of milk for cheesemaking was opposed by cheesemakers. In Canada, less concern is expressed about the safety of raw-milk aged hard cheeses, since populations of pathogens, including Salmonella, E. coli, and Listeria, decline during aging. However, populations of L. monocytogenes increase during storage in soft and semisoft cheeses. Of four outbreaks in Canada in 2002, three involved Listeria contamination of cheeses made from pasteurized or heat-treated milk. Therefore, Canada is developing a policy to replace the 60-day aging period for soft and semisoft cheeses by strengthening production criteria and end-product testing. Through stringent raw milk production, improved process controls, and use of performance criteria, improvements in safety of raw-milk cheese can be achieved.
Australia does not allow raw-milk cheese to be produced domestically but allows it to be imported. Risk assessments concluded that Swiss semi-hard raw-milk and hard Parmigiano Reggiano cheeses are as safe as cheeses manufactured from pasteurized milk. A 2005 draft risk assessment revealed that Roquefort presented a low risk for health and safety and was deemed acceptable for importation because it can be produced to the same level of safety as blue cheese manufactured from heat-treated milk.
The U.S. National Academies of Science has recommended a move away from a requirement for mandatory pasteurization or a 60-day aging period to implementation of performance standards that specify a reduction in numbers for a target pathogen (NAS, 2003). This approach is similar to what has been embraced by Food Standards Australia New Zealand, which notes that manufacturing processes for very hard cheese can achieve a 5-log reduction of bacterial pathogens of concern when using raw milk, given good hygienic and manufacturing practices. These approaches are in harmony with European Union directives which establish microbiological criteria for raw milk and raw-milk cheeses.
The safety of raw-milk cheeses can be better assured through adoption of performance standards and microbiological criteria than through current requirements which focus on pasteurization or aging. Such measures will ensure that consumer demand for raw-milk cheeses can be safely met.
by Catherine W. Donnelly, a Professional Member of IFT and Co-Director of the Vermont Institute for Artisan Cheese, is Professor, Dept. of Nutrition and Food Science, University of Vermont, 200 Carrigan Hall, Burlington, VT 05405 ([email protected]) .
Altekruse, S.F., Timbo, B.B., Mowbray, J.C., Bean, N.H., and Potter, M.E. 1998. Cheese-associated outbreaks of human illness in the United States, 1973-1992: Sanitary manufacturing practices protect consumers. J. Food Protect. 61: 1405-1407.
Reitsma, C.J. and Henning, D.R. 1996. Survival of enterohemorrhagic Escherichia coli O157:H7 during the manufacture and curing of Cheddar cheese. J. Food Protect. 59: 460-464.
NAS. 2003. Scientific criteria to ensure safe food, Natl. Acad. of Sciences, National Academies Press, Washington, D.C.