By: Candess Zona-Mendola

Listeria in cheese has lately become what E. coli is to beef, a pathogen seen too often in the same food. It is a vicious cycle; one that lends a lesson to be learned. How does Listeria get into cheese? More importantly, why is it still getting into cheese?

The Cheese-Making Process

To understand how certain foods become contaminated, it is a good idea to examine the process in which they are created. Cheese-making, when prepared without an attention for food safety, can be an especially hazardous process – much like home canning snafus could lead to botulism. Listeria bacteria can be introduced to a cheese during any stage of its making process. Depending on the recipe, there may not be a kill step to prevent it from making it into the final product.

First, the fromager, or cheese maker, starts with warming the milk. As an aside, this is a much different process than pasteurization. Pasteurization usually involves heating milk quickly to a high temperature, anywhere from 165-280 degrees Fahrenheit for a short period of time. The method of warming milk for cheese-making may only reach about 120 degrees Fahrenheit, not a temperature high enough to effectively kill any dangerous bacterial contaminates. Therefore, if a bacteria is already present in the raw milk base, it is there to stay without a kill step.

The following step of the process is called “direct acidification,” or the introduction of a material to make the batch more acidic. This can be accomplished through adding vinegar or citric acid to the batch or even living, bacteria cultures. The addition of ingredients and more bacteria could also be a cause for contamination.

Next, a coagulant (or enzyme used to bind together proteins) is added to the batch. This addition helps the batch become a solid gel. Combined with time, the batch becomes a semi-solid curd, much like the texture and sponginess of memory foam. This curd is then cut down with a knife in varying sizes, depending on how much moisture the fromager wants left in the final product. The smaller the cuts in the curd means the drier and more “ageable” the cheese.

The curd is then cooked from several minutes up to an hour depending on the fromager’s cheese recipe. This allows the acid to develop inside the curd. As cheese is cooked, it becomes drier. Again, this process is different than pasteurization and the cheese does not usually reach the target bacteria-killing temperature. Through the cooking process, whey is removed from the batch and replaced with water. The curds are then drained and pressed together into a form, usually a circle or a cheese wheel.

The last step is salting and aging. The aging process allows bacteria to continue to grow in the cheese, making it taste more pungent. Depending on the bacteria, the taste, texture, and composition of the cheese can be affected. According to a 2012 study conducted at Harvard University, “[c]ommunities of microbes catalyze the transformation of milk into cheese and remain active participants in the development of a cheese throughout the aging process.” This means bacteria present in any ingredient or introduced during the cheese-making process continues to grow as the cheese ages.

Raw Milk – The Dangerous Base Ingredient

Raw milk is dangerous, and in this outbreak, is the base ingredient for Vulto Creamery’s cheeses. Despite what raw milk enthusiasts have argued, there is virtually no way to keep raw milk safe for drinking. It is a food that many support as a “superfood,” but few take into account that the cons outweigh the pros. The cleanest, greenest dairy farmers cannot guarantee a completely pure raw milk product. This is the main reason why raw milk cheeses are at a higher risk for foodborne pathogen contamination. Pursuant to a recent article from Popular Science, “the most common foods to be contaminated with listeria are raw dairy products and produce.”

UnsafeFoods’ Raw Milk Diaries focuses on this very subject. A recent campylobacter bacteria in raw milk outbreak in the United Kingdom illustrated this very concern, that raw milk products, even those procured from exceptional farms, are dangerous. The Low Sizergh Barn fits the exact definition of the perfect dairy – family-owned for many years, award-winning, the presence of healthy, well-tended, grass fed cattle, new age milking methods, and a location surrounded by nothing but fields upon fields of grass. Their idyllic business had it all, except pasteurization. The lack of this kill-step process for their products lead to a major outbreak that sickened over 60 people aged one to 89 years old.

According to the Centers for Disease Control and Prevention (CDC), “even dairy farms with very good safety practices can harbor illness-causing germs. And even if a batch of a farm’s raw milk tests come back negative, it is no guarantee that the next batch will be free of harmful germs.”

Listeria: The Bacterium that Keeps On

Listeria is hardy. It thrives in room and freezing temperatures. It can survive in salty environments, like the salt introduced to a cheese during the aging process. There is only one way to rid a food of Listeria and that is heating – through pasteurization and/or heating to optimum cooking temperature.

Whether Listeria was already present in the raw milk from the local dairy farm or introduced via cross-contamination during the cheese-making process, raw milk soft cheeses are already a risk for foodborne illness. They start raw, are not heated to optimum cooking temperatures, and are considered ready-to-eat after the aging process is over.

How is This Related to the Vulto Creamery Outbreak?

The cheeses subject to Vulto Creamery’s recall and recent expansion are most likely made in a method similar to the process noted above. As they are soft raw milk (unpasteurized) cheeses, there potentially was a lack the presence of a kill step in the cheese-making process. As the cheeses age, the Listeria contamination only grows. As these cheeses are usually served without being first heated, the Listeria bacteria is not killed prior to ingestion.

What Can I Do to Prevent Illness?

The CDC, FDA, and state local health departments recommend that any cheeses involved in the Vulto Creamery outbreak and recalls not be eaten. For pictures of the affected cheese products, you can visit the FDA’s website here. As Listeria is especially concerning for those who are very young, the elderly, patients with compromised immune systems, and pregnant women, the CDC recommends these high risk individuals avoid unpasteurized raw milk cheeses. Those in the high risk group are in danger of developing Listeriosis and potentially, severe complications – like meningitis, bacteremia, and potentially miscarriage or still birth in pregnant women.

If you or someone you care about has eaten any cheeses subjected to the Vulto Creamery Outbreak or Recall, and are ill, medical attention is advised. For more information about this outbreak or recall, you can visit our past posts here.