The Microbiological Dangers of Unpasteurized Cheese
Raw cheese is made from unpasteurized milk, which means it has not been heated to a specific temperature for a set time to kill potentially harmful bacteria. While many proponents argue for superior flavor and nutritional profiles, the lack of pasteurization creates a significant food safety hazard. Milk can become contaminated in various ways on a farm, including from infected animals, the milking environment, or animal feces.
Key Pathogens Found in Raw Cheese
The most common and dangerous pathogens found in raw milk and raw cheese include:
- Listeria monocytogenes: This bacteria can survive and grow in cold temperatures, including inside a refrigerator, and has been linked to numerous outbreaks from soft cheeses. Listeriosis is particularly dangerous for pregnant women, newborns, older adults, and those with weakened immune systems, potentially leading to miscarriage, stillbirth, or death.
- Shiga toxin-producing E. coli (STEC): Some strains of E. coli, such as O157:H7, can cause severe bloody diarrhea, abdominal cramps, and vomiting. In vulnerable populations, it can lead to hemolytic uremic syndrome (HUS), a life-threatening kidney failure.
- Salmonella spp.: This common bacteria causes salmonellosis, with symptoms including fever, diarrhea, and abdominal cramps. Outbreaks linked to raw milk cheese have been documented in recent years.
- Campylobacter spp.: The leading cause of bacterial foodborne illness in the US, Campylobacter infection can cause severe diarrhea. In rare cases, it has been linked to Guillain-Barré syndrome, a form of paralysis.
- Staphylococcus aureus: This bacteria can produce toxins that cause sudden and severe food poisoning, including vomiting and nausea, and can withstand heat treatments.
The Impact of Cheese Type on Risk
The safety risk of raw cheese is not uniform across all varieties; it is heavily influenced by the cheese's moisture content, pH level, and aging process.
| Cheese Type | Characteristics | Associated Risk Level | Reason for Risk Variation |
|---|---|---|---|
| Soft Cheeses (Brie, Camembert, Feta) | High moisture, lower acidity, shorter aging | Highest | Favorable environment for bacteria growth; minimal aging to kill pathogens. |
| Semi-Soft Cheeses (Gouda, Edam) | Moderate moisture content | Moderate | Some aging occurs, but still retains enough moisture for some bacteria to survive and grow. |
| Hard Cheeses (Cheddar, Swiss, Parmesan) | Low moisture, higher acidity, long aging (typically >60 days) | Lowest | Conditions are generally inhospitable to most pathogens, but residual risk remains. |
The Role of Aging and Regulation
In some countries, regulations require raw-milk cheeses to be aged for a minimum of 60 days before sale. The theory is that the aging process, combined with factors like lower pH and moisture, is sufficient to kill or inactivate harmful bacteria. However, this is not a foolproof guarantee. Recent research and outbreaks have shown that pathogens like Salmonella can persist even in 60-day aged raw cheeses. Furthermore, the aging process's effectiveness against emerging threats like avian influenza in dairy products is not fully understood. The only method proven to eliminate these risks is pasteurization.
Who Should Avoid Raw Cheese?
Because the risks are not fully mitigated, health authorities universally recommend that certain populations avoid raw cheese entirely.
- Pregnant women: Listeriosis infection can cause miscarriage, premature delivery, and newborn health complications.
- Infants and young children: Their immune systems are still developing, making them more susceptible to severe illness from pathogens like E. coli and Salmonella.
- Older adults: Age-related weakening of the immune system increases their vulnerability to foodborne illness.
- Immunocompromised individuals: This includes people with conditions like HIV, cancer, or those undergoing treatments such as chemotherapy. Their weakened defenses make them highly susceptible to serious infection.
For the general population, the decision to consume raw cheese is a personal one, weighing the potential health benefits of unpasteurized foods against the documented risk of severe illness. Reputable, well-established brands and careful storage are crucial, but complete safety cannot be guaranteed. For those at higher risk, cooking raw-milk cheeses thoroughly (to at least 165°F) is a safe way to enjoy the product.
Conclusion
While raw cheese may offer a distinct flavor, it poses documented health risks due to potential contamination with harmful bacteria. The pasteurization process was developed to eliminate these threats, which historically caused widespread outbreaks. Despite advancements in modern dairy farming, a residual risk remains, especially with soft, unaged raw cheeses. For vulnerable individuals, the consensus among public health experts is clear: the risk of serious, potentially fatal foodborne illness far outweighs any perceived benefits. Therefore, choosing pasteurized alternatives or properly cooking raw-milk cheeses is the safest approach.
