2007 Pilot Project Cheese Results Summary
- concerning the period of June to December, 2008

Pasteurized Milk Cheese
Forty-five samples of cheese from ten farms were tested. Most of these samples were from fresh lactic, Feta, bloomy-rind, and Ricotta cheeses. There were also three samples of flavored Cheddars, one sample of Cheddar, and four samples of yogurt.

• No pathogens, E. coli, or Listeria species were found in any of the samples.
• No Staph toxin was found in the seven samples that were tested.
• Ten samples had coliform counts greater than 10 CFU per gram (colony forming unit, which is equivalent to one bacteria).
• Six of these samples had coliform counts greater than 100 CFU per gram.
• Only one sample had greater than 1,000 CFU per gram.

These results show that 78% of the cheeses (35 out of 45) were in compliance with regulations for coliform levels in the northeastern states allowing less than 10 CFU per gram. All of these states: VT, NY, ME, MA, CT, and NH use either a level of less than 10 or less than 100 CFU per gram. By comparison, 87% of these cheeses (39 out of 45) were in compliance with EU regulations for coliform levels, which must be less than 100 CFU per gram in pasteurized cheeses. All of the cheeses were in compliance with the regulations in northeastern states for absence of E. coli and pathogens. In the USA there is no specific regulation for levels of Staphyloccus aureus but these must be less than 100 CFU per gram for pasteurized milk cheeses in the EU.

Minimizing exposure to the environment, good sanitation, fast cooling to 40 F, tight packaging, and storage at 38 F or less helps to minimize the growth of coliform bacteria.

Raw Milk Cheese

Ninety-five samples of cheese from 18 farms were tested. These samples were from a broad spectrum of cheese varieties, including soft-ripened, blue, Feta, tomme, washed-curd, and hard Cheddar and Alpine cheeses.

• Seven samples from five different farms tested positive for Listeria species but none of these samples contained the Listeria monocytogenes pathogen. The identification of the Listeria species was done at a dairy product-testing lab in Minnesota.
• Salmonella pathogens were not found in any of the samples.
• No Staph toxin was found in the two samples that were tested.
• E. coli pathogens (0157:H7) were found in 6 samples.
• Ten samples had E. coli counts greater than 10 CFU per gram.
• Five of these samples had E. coli counts greater than 100 CFU per gram.
• Two of these samples had E. coli counts greater than 1,000 CFU per gram.
• One sample had an E. coli count greater than 10,000 CFU per gram.
• Thirty-seven samples had coliform counts greater than 10 CFU per gram.
• Twenty-eight of these samples had coliform counts greater than 100 CFU per gram.
• Eighteen of these samples had coliform counts greater than 1,000 CFU per gram.
  
• Eight of these samples had coliform counts greater than 10,000 CFU per gram.
• Several of the soft-ripened bloomy and washed-rind cheese samples had high levels of non-coliform bacteria, which were most likely associated with the rind.

These results show that 39% of the cheeses ( 37 out of 95) were not in compliance with the most common regulation for coliform in the northeastern states of less than 10 CFU per gram. Ten percent (10 out of 95) were not in compliance with regulations in the northeastern states for absence of E. coli. By comparison, only one out of the 95 samples had an E. coli count greater than 10,000 CFU per gram and was not in compliance with regulations in the EU for levels of E. coli in raw milk cheeses. In addition, six samples (6% of the cheeses) contained pathogenic E. coli and were therefore not in compliance with EU regulations for raw milk cheese.. Interestingly, the sample with >10,000 coliform per gram did not have any pathogenic E. coli. This actually shows that only one sample was over the critical limit in the EU, which would have required further testing for pathogenic E. coli. In contrast, ten samples were over the critical limit used in this pilot project (< 1,000 CFU/gram) and were tested for pathogenic E. coli and six samples were positive for the pathogen.

Perhaps the level for E. coli is set this high in the EU because the risk of illness from pathogenic E. coli is not serious unless levels of all E. coli rise above 10,000 CFU per gram. I have read articles that high levels of E. coli are evident in raw milk cheeses like traditional French Camembert (in 1-2% of these cheeses) and there is regulatory pressure to allow micro filtration, which is a form of pasteurization, into the process for the larger-scale cheesemaking operations in Normandy. However, there was no indication in these articles that anyone had become ill from eating the traditionally-made raw milk cheese.

In our project, the batches of cheese containing the high levels of E. coli and pathogens were not sold thereby eliminating the health risk to consumers. Since our critical limit was lower than that used in the EU, we were being more cautious in our perception of where the level of risk is.

Pasteurized milk cheese compared to raw milk cheese

Pilot Project

The raw milk cheeses had much higher counts of coliform and E. coli compared to the pasteurized milk cheeses. However, as a percentage, the number of samples of raw milk cheese exceeding the critical limits used in the pilot project was slightly higher than the number of pasteurized milk cheese:

• six samples (about 13%) of pasteurized milk cheese were not in compliance with the critical limit for coliform (<100 CFU per gram)
• 18 samples (about 20%) of raw milk cheese were not in compliance with the critical limit for coliform (<1,000 CFU per gram).

Northeastern States (USA)

If the most stringent regulations for coliforms of less than 10 CFU per gram, such as in CT and MA, were used for all of the cheeses the results would look a lot different:

• ten samples (about 20%) of pasteurized milk cheese were not in compliance with the critical limit for coliform (<10 CFU per gram).
• 37 samples (39%) of raw milk cheese were not in compliance with the critical limit for coliform (<10 CFU per gram).

European Union (EU)

These standards are more tolerant than those of the pilot project.

• six samples (about 13%) of pasteurized milk cheese were not in compliance with the critical limit for E. coli (<100 CFU per gram)
• Only seven samples (about 8%) of raw milk cheeses were not in compliance with EU standards for E. coli in raw milk cheeses (<10,000 CFU per gram) and the absence of pathogens. One sample was above the critical limit and six samples contained the E. coli pathogen.

The highest coliform and E. coli counts were generally found in the soft-ripened and washed-curd cheeses; these cheeses accounted for 20 of the 28 samples with coliform counts of greater than 100 CFU per gram. Hard cheeses did not pose as great of a risk as these higher moisture types of cheese.

It seems from these results that the pilot project cheesemakers would have a challenge to meet current US limits for coliform and E. coli in cheeses if the testing frequency used by regulators were the same as used in the pilot project. Cheeses samples were tested approximately once per month in the pilot project. This is certainly not the case with the regulators; the most frequent testing for cheese is done every three months in MA and CT. In addition, a risk assessment is not made and often the hardest cheeses are sampled instead of the softer, higher moisture cheeses, which pose a greater risk to consumers. Since out regulatory system allows farmers and cheesemakers time for corrective action to achieve the critical limits, it is possible to for cheesemakers to meet this challenge and bring their operations back into compliance. In fact, pilot project cheesemakers who did find high levels of coliforms and E. coli in their cheeses were able to lower their counts below the critical limits within two months. This is less than the typical time that is granted by the regulators for corrective action, which is three to four months. This result is most likely due to the greater testing frequency, the assistance of the field person with problem solving, and the farmers and cheesemakers learning more about food safety and quality control.

Sources of Contamination

There was a correlation between coliform counts in raw milk in excess of 100 CFU per ml and high coliform counts in cheese. There was also a correlation between environmental samples with coliform counts in excess of 100 CFU per gram from equipment such as drain matting and shelving materials and high coliform counts in cheese. Coliform and E. coli levels were lowered to acceptable limits on all farms by the fifth month of the pilot project. Sources of contamination were identified and some practices were changed and new ones were started:

• Sources of coliform contamination at the farm were identified and controlled.
• Equipment that is very hard to clean thoroughly, such as plastic drain matting, was given a heat treatment in 170 F or hotter water for 5 minutes.
• Shelving materials such as plastic racks and matting were changed more frequently during the aging process.
• For fresh pasteurized milk cheeses the exposure to air was minimized and faster cooling as implemented.
• Refrigerated spaces for pasteurized milk cheeses were cleaned and sanitized more regularly.
• Brines were changed and the practice of sampling brines every other month for coliforms began.

The sources of positive Listeria samples were puzzling. Some positive Listeria counts went away as environmental cleaning such as in drains was implemented more regularly. Other than this it has been hard to pinpoint the source of Listeria contamination. The presence of non-harmful Listeria species indicated that pathogenic Listeria might have not been far behind (or somewhere else in the picture). The test results, especially from environmental swabs, helped cheesemakers to identify potential sources of pathogenic contamination in their cheeses.

High counts of Staphyloccus aureus (> 2,000 CFU per ml) in raw milk triggered a test for the toxin, which these bacteria produce, in cheese. None of the toxin was found in nine cheese samples (seven from pasteurized milk cheese and two from raw milk cheese). It is accepted food science that there need to be 100,000 CFU per ml of Staph in a food to have enough toxin to make someone ill. The reason for testing the cheese even when a much lower level of Staph is found in raw milk is that there could be additional growth during cheesemaking and aging, during which time enough toxin could be produced.

Final thoughts

The pilot project provided an adequate system for reducing the risk of pathogens in raw and pasteurized milk cheeses made by eighteen farmstead cheesemakers. It also served to improve the overall quality of cheeses made on the farms. Cheesemakers were able to get more frequent results of tests from samples of their raw milk, the environment, and their cheeses than had occurred previously. They learned how to use these results to assure product safety and improve cheese quality. Many cheesemakers appreciated having a technical field person, who was also a farmstead cheesemaker, to help them with questions about reducing risk (consumer safety), cheesemaking recipes, quality control, and other related issues pertaining to operating their cheese businesses.

In setting critical limits for contaminants in cheese, it seems that a double standard exists with regards to critical limits of coliform and E. coli between raw milk cheeses made in the USA and in the EU. The limits used in the pilot project were a compromise. It is interesting to note that many raw milk cheese samples regularly had levels of coliform <10 CFU per gram. This proves that it is certainly possible to achieve this low level. The more interesting question is if it is necessary to have this low level in raw milk cheeses. Perhaps, there should be a change in the US regulations toward the differentiation of critical limits for coliform and E. coli according to the type of cheese being tested as is done in the EU. This involves performing a more complicated risk assessment of the safety of raw milk cheeses that is based on the chemical and biological properties of the cheeses.

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