Dairy Sheep Symposium - the Department of Animal Sciences ...

LATEST DEVELOPMENT IN THE USE OF RAW MILK FOR CHEESEMAKING
W.L. Wendorff
Department of Food Science
University of Wisconsin, Madison
Madison, Wisconsin
Introduction
Since 1949, cheesemakers could use one of two methods to assure the safety of cheese that
they produced: 1) pasteurize milk intended for cheesemaking or 2) hold the finished cheese at a
temperature of not less than 35°F for at least 60 days (US FDA, 2000). Research over the years
has shown that various pathogens can survive well beyond the mandatory 60 day aging period in
various cheeses (Table 1). In April 1997, FDA ask the National Advisory Committee on Microbiological
Criteria for Foods if a revision of the policy requiring a minimum 60 day aging period
for raw milk hard cheeses was necessary to ensure the safety of hard cheeses for U.S. consumers
(Donnelly, 2001). Some of this concern was initiated when Wisconsin temporarily lost the TBfree
status due to TB-contaminated animals being transported in from Upper Michigan (Anonymous,
1995). Additional concerns came from a report by Reitsma and Henning (1996) detailing
the survival of E. coli 0157:H7 in aged Cheddar cheese. The Institute of Food Science and
Technology (IFST) in the UK also issued a caution on the potential health hazards posed by
pathogenic bacteria in raw milk cheeses, especially soft and semi-soft cheeses (IFST, 2000). In
1999, FDA initiated challenge studies with E. coli 0157:H7 in raw milk Cheddar cheese to
determine the effectiveness of the aging period in eliminating the potential pathogen. At the
same time, they started a comprehensive review on the safety of raw milk cheeses.
The American Cheese Society, in conjunction with Oldways Preservation and Exchange
Trust and the Cheese Importers of America, were very concerned with the potential that FDA
may ban raw milk cheeses. In March 2000, they formed the Cheese of Choice Coalition to work
with FDA to preserve their ability to manufacture and import raw milk cheeses under the existing
food regulations. In November 2000, they hired Dr. Catherine Donnelly of the University of
Vermont to assist in a thorough review of the past safety of raw milk cheeses. She recently
presented her findings at this year’s American Cheese Society meeting in Louisville, KY
(Donnelly, 2001). Following is a summary of her findings:
Reviews on Safety of Raw Milk Cheeses
Johnson et al. (1990) conducted a comprehensive review of epidemiological literature from
1948-1988. They identified only six outbreaks of illness transmitted via cheese produced in the
U.S. during this period. The use of raw milk was a factor in one outbreak each in the U.S. and
Canada. No outbreaks were reported for hard Italian cheeses, such as Parmesan, Romano and
Provolone. In rare instances, Swiss and Cheddar cheeses were linked in outbreaks.
Altekruse et al. (1998) reviewed all cheese associated outbreaks reported to the CDC during
the period 1973-1992. There were 32 cheese-related outbreaks, 11 of which could be attributed
to contamination at the farm during manufacturing or processing. Of the 11 outbreaks, 5 were
related to consumption of Mexican-style soft cheese whereas only 1 outbreak was related to
Cheddar cheese. The authors suggested that aging alone may not be a sufficient pathogen control
step to eliminate Salmonella, Listeria, and E. coli 0157:H7 from cheese.