HIGH COLIFORM COUNTS IN CHEESE

Sometimes there are test results in the cheese that have very high coliform counts, e.g. >1500.

As long as the E. coli is <10, I would not be not concerned about the safety of the cheese for consumption. However, the high coliform count indicates a breakdown in sanitation and there must be a way to improve things. This is the way I use the coliform count; it gives me a reason to investigate the conditions that the cheese is made under so that I can make improvements to the process.

I have had cases of high coliform counts (>1500) in a soft-ripened, washed- rind cheese. The counts were lowered with improved sanitation, e.g. we noticed that the plastic matting and racks that the cheeses were on stayed very moist and were hard to keep clean. We rotated these pieces of equipment more frequently and kept them cleaner and drier. The coliform was reduced to counts of at least <100 and mostly around <10-30. This cheese is aged about 90-100 days. During the first 60 days the rind is always moist because we are smearing it with brine solution. The young cheeses have pH 5.3-5.4, which increases significantly during aging.

I know that if there are 100-1,000 coliform in the raw milk they will not survive in the cheese if the pH drops below 5.5 in 5 hours from adding starter. I learned this from another cheesemaker that was finding high coliform counts in some raw milk cheeses the day after cheesemaking started. He was from a pasteurized cheesemaking background where it is routine to test cheese early in the process (before aging) to monitor the quality and determine points in the process where coliform are getting in. He was very surprised to find coliform in the cheese at this time and, rather than assuming that the aging process would reduce the coliform, he wanted to find the source and figure out how to control the growth during the cheesemaking process. The coliform was traced back to the raw milk. The farmers were milking by hand and the milk was being delivered in cans to the creamery. During cheesemaking the coliform would grow from 100 up to as high as 10,000 during the early stages but the they would be reduced to <100 if the pH dropped to 5.5 in 5 hours from adding starter. Survival of coliform from that point on was very poor and the counts in the finished cheese were reduced to <10.

Imported raw milk cheeses are allowed by the EU and FDA to have up to 10,000 coliform. In the US, if regulators in individual states take samples and test for coliform the maximum level is usually set at 10 or 100. I think that the reason imported cheese coliform levels are allowed to be higher is because many of these cheeses are still made under rough conditions with hand milking out in the open and more rustic cheese rooms with some wooden equipment being used. Therefore, the milk may have higher coliform levels to start with than machine made milk and the cheeses may not have the type of rapid acid development that will inhibit them.

Interestingly enough, I have repeatedly found coliform on my wooden cheese hoops. These hoops have been swabbed and tested many times in an attempt to prove that the wood inhibits coliform. Research has shown that wood kept in proper condition will inhibit the growth of pathogens but I doubt that wood is entirely "coliform free." Remember that things are tested for coliform bacteria because these are "sanitary indicator microorganisms." They show that bacteria are there that are not an original part of the food or equipment being tested. Wood is not considered to be sanitary, which is why many inspectors and regulators have a phobia about it and don't want to see it anywhere near the cheese. So, a distinction must be made between cheeses that are free of E. coli, which is a fecal coliform and pathogens and cheeses that are free of coliform. Pasteurized milk cheeses should by all means be free of coliform since the milk is starting out coliform free. Cheeses made from pasteurized milk should have a rapid pH drop to prevent contaminants from growing.

Raw milk cheeses are also made with rapid acidification so that coliform growth is severely inhibited or sometimes with slower acidification rates so that there is an opportunity for coliform survival. I have made several varieties of raw milk cheese that do not achieve a drop to pH 5.5 in 5 hours. Tomme-style cheese is typical of this slower acidification approach to cheesemaking where the drop to pH 5.5 may take 10-12 hours.. The philosophy of this approach is that the character of the cheese is governed more by the diversity of the micro flora in the milk and “beneficial contaminants,” which get in to the curds during cheesemaking, rather than the starter culture alone. In my opinion the bottom line is that the cheeses should be free of pathogens. Where the bar is set for allowable levels of coliform is debatable.

I make a hard cheese in the wooden cheese hoops that has a cook temp of 112 F and the pH drops to 5.5 to 5.6 in 5-6 hours from adding starter. The cheese is aged for at least 6 months and develops a very hard, dry rind. The young cheeses have pH 5.3-5.4. I have had several batches of this cheese tested and there has been <10 coliform in every batch. This example can be juxtaposed with my (previously mentioned) soft-ripened, washed-rind cheese that was aged on the plastic equipment. The soft-ripened cheese was set at 93-94 F and the pH was only down to 5.9-6.0 within 5 hours from adding starter. The milks in the vat going in to these cheeses are generally <50 coliform. This milk is being tested in the cheese vat after taking one hour for delivery in 10-gallon cans on the back of a truck; sometimes the milk is 55 F when it is poured into the vat. The milk at the farm is consistently <10 coliform. There may be some growth of coliform during cheesemaking and the equipment may also contribute coliform. These two examples demonstrate that the process can control the coliform and that equipment can contribute to the growth of coliform.

I have done away with most of the plastic mats and racks and have all of the cheese on either wooden boards or stainless steel wire racks. The cheeses have been low in coliform (<100) for the past several months. I have found plastic matting to be problematic in the past. I think that I have told some of you the story about my experience many years ago of making Brie and Camembert cheeses. I was using a “multi-mold” system that employed plastic block forms that sat on plastic mats and stainless steel drain trays. At one point in our history, a much larger cheese company that had a standard for coliform, which we were not meeting, was selling our cheese. I am fairly sure that it was <10 because we were making a pasteurized milk cheese. The quality control chief came to our creamery and checked the different pieces of equipment and the environment taking numerous swabs. The results showed that the plastic mats were the source. We washed them even harder and soaked them in the sanitizer even longer but could not eliminate the coliform. We finally resorted to cooking them in our vat pasteurizer at 170 F for at least 5 minutes to get them clean enough! We continued to do this as part of our cleaning/sanitizing routine from then on.

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