Some say raw milk cheeses are being beat-up by US regulators this year. Indeed, if there was a Food Safety Zodiac, 2010 would be the Year of the Cheese (shell eggs a close second). Whatever the underlying explanation, the number of cheese-related illnesses and recalls in 2010 appears unprecedented. While covering these events, my blog has been inundated with comments expressing outrage at FDA and state regulators for raw milk cheese “crackdowns.” The comments range from fringe screams about food Nazis and fascists to thoughtful and informative discussions about the microbiology of raw milk cheeses and implications for food safety and quality.

Tami Parr of the Pacific Northwest Cheese Association portended regulatory changes that may affect the fate of raw milk cheeses on her blog earlier last month. Interestingly, she links to a 1997 memo that recommended FDA re-examine its 60-day aging process for hard cheeses made from raw milk. No changes were made to the rule at that time, but clearly the issue of aged raw milk cheeses and food safety is not new, as shown in the timeline below.

To look at the issue closer, this paper provides an overview of the historical context and timeline of raw milk cheese regulations in the US, and examines the state-of-the-science surrounding the 60-day aging rule established by FDA.  I have broken it into 5 parts for ease of reading.  At the end of part 5, I will provide the entire paper in PDF.

I welcome comments, suggestions, and additional literature from readers to add to the analysis.

Historical Perspective

Timeline of Key Studies and Regulatory Changes for Cheeses Made from Raw Milk

1941-1944: Typhoid fever epidemics are linked to cheddar cheese made from raw milk in Canada; outbreak-related Salmonella typhi strains are recovered from 30-day-old cheese, but not from 48- or 63-day-old cheese resulting in Alberta, Canada halting the sale of raw milk cheese unless ripened for at least 90 days (Marth 1969).

1946: Brucella abortus is found to survive in cheddar cheese made from raw milk for up to 6 months depending on initial inoculation level, but the authors of the study conclude that cheddar cheese is not a proven carrier of undulant fever (the human disease caused by B. abortus). D’Amico (2008a) suggests that this study, combined with the earlier data on typhoid fever illnesses not attributed to cheese cured for more than 63 days, is the likely origin of the 60-day curing period in the US. However, subsequent reports in the 1940’s show extended survival of Mycobacterium tuberculosis (>100 days), Salmonella typhi (3-10 months), and hemolytic Streptococcus (>160 days) in cheddar cheese (D’Amico 2008a).

1950: FDA promulgates regulations (21 CFR Section 133) requiring that cheesemakers use pasteurized milk, or cure the cheese for no less than 60 days at a temperature greater than 35°F. According to D’Amico (2008a), there are over 30 natural cheeses that can be made legally from raw milk in the US under this rule.

1960’s: Additional challenge studies show survival of pathogens including Salmonella enterica subtype Typhimurium beyond the 60 day curing period; Salmonella typhi is found to survive in stirred curd granular cheddar cheese for 150-180 days when held at refrigeration temperatures (D’Amico 2008a).

1987: Numerous foodborne illnesses are linked to commercial fluid raw milk including 22 deaths from Salmonella Dublin infections from 1971-1975 (Werner 1979). This prompts a Citizen’s Petition and federal judge’s ruling that orders the FDA to ban fluid raw milk and milk products from interstate commerce (21 CFR Section 1240.61). The regulations allowing cheesemakers to sell cheese made with raw milk if cured for 60 days at a temperature greater than 35°F remain in place (21 CFR Section 133).

1973-1992: CDC reviews reported outbreaks and illnesses from raw milk (Headrick 1998) and cheeses made from raw milk (Altekreuse 1998). During this time, there were 32 reported cheese-associated outbreaks and 58 deaths, but the authors conclude that “If current Food and Drug Administration sanitary requirements for cheesemaking had been met, these outbreaks would have been preventable.” They go on to say: “Curing cheeses kills most bacteria present in cheeses; however, evidence from sources other than the CDC Foodborne Disease Outbreak Surveillance System suggests that curing alone may not be a sufficient pathogen control step to eliminate Salmonella, Listeria, and E. coli O157:H7 from cheese.”

1996: Researchers at South Dakota State University publish a study showing that 60-day aging is largely ineffectual in reducing levels of E. coli O157:H7 in cheddar cheese. FDA then asks the National Advisory Committee for Microbiological Criteria for Food (NACMCF) to re-examine the literature on the efficacy of 60-day aging. In a memo to FDA, the committee states: “the sixty-day aging process for hard cheese is questionable as an effective measure in support of the public’s health.”

2002: Health officials from Alberta, Canada report an outbreak of E. coli O157:H7 hemorrhagic colitis associated with Gouda cheese made from raw milk (Honish 2005). In their paper, the authors suggest that Canada re-evaluate the federal regulations for aging of hard cheeses made from raw milk.

2004: In an interview with Food Safety Magazine, FDA officials state that they are developing a “risk profile for raw milk cheeses, which will aid in the Agency’s assessment of the requirements for processing these cheeses,” based, in part, on the report by the NACMCF and other recent research suggesting that 60-day aging may be insufficient to protect the public’s health (Sheehan 2004).

2006: Schlesser and colleagues report results from a study of E. coli O157:H7 survival in cheddar cheese made from raw milk, and confirm previous reports questioning the efficacy of 60-day aging to eliminate E. coli O157:H7 during cheese ripening.

2008: D’Amico and colleages determine that the 60-day aging requirement does not ensure safety of surface-mold-ripened soft cheeses manufactured from raw or pasteurized milk when Listeria monocytogenes is introduced as a postprocessing contaminant. The authors conclude that “the safety of cheeses of this type must be achieved through control strategies other than aging, and thus revision of current federal regulations is warranted.”

2010: According to press quotes, FDA officials are conducting a nationwide survey of cheese safety with a focus on Listeria monocytogenes contamination. Notably, this survey encompasses both raw and pasteurized cheese products from large and small cheesemakers.

In November, the CDC reports 38 illnesses from Gouda cheese made from raw milk and aged for 60 days in accordance with regulations (CDC, 2010).

A study in the December 1, 2010 issue of the Journal of Food Protection documents survival of E. coli O157:H7 in aged Gouda and stirred-curd cheddar cheese (D’Amico 2010). The authors conclude that “the 60-day aging requirement is based on decades-old research indicating that Brucella abortus is eliminated in cheddar cheese alone is insufficient to completely eliminate levels of viable E. coli O157:H7 in Gouda or stirred-curd cheddar cheese manufactured from raw milk contaminated with low levels of this pathogen.“


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  • Carl Custer

    Some older papers:
    Park, H. S., E. H. Marth, J. M. Goepfert, and N. F. Olson. 1970.
    The fate of Salmonella typhimurium in the manufacture and ripening
    of low-acid Cheddar cheese. J. Milk Food Technol. 33:280–284.
    Park, H. S., E. H. Marth, and N. F. Olson. 1973. Fate of enteropathogenic
    strain of Escherichia coli during the manufacture and ripening
    of Camembert cheese. J. Milk Food Technol. 36:543–546.
    Frank, J. F., E. H. Marth, and N. F. Olson. 1977. Survival of enteropathogenic
    and non-pathogenic Escherichia coli during the manufacture
    of Camembert cheese. J. Food Prot. 40:835–842.

  • Dog Doctor

    Mr. Marler, thank you for the research information and the article.

  • Thanks Carl, I’ll review and add.