Blue cheese is a type of cheese that is made from cow, goat, or sheep’s milk and has had cultures of the mold Penicillium added so that the final product is riddled with blue-green veins. Blue cheese gets its unique tangy, pungent, and slightly salty flavor from the mold cultures breaking down and utilizing the milk’s fats and proteins. The process of adding the mold spores and allowing the cheese to age creates a very low pH cheese that is inhospitable to many bacteria that could cause foodborne illness. However, blue cheese is a perishable food and leaving it unrefrigerated for too long can still allow harmful microbes to grow and increase the risk of foodborne illness. So how long is too long when it comes to leaving blue cheese out?
General Food Safety Guidelines
The United States Department of Agriculture (USDA) provides some general food safety guidelines regarding how long various foods can be left unrefrigerated before they become unsafe to eat. These include:
- Refrigerate or freeze perishables, prepared foods, and leftovers within 2 hours.
- Never thaw foods at room temperature. Thaw in the refrigerator, under cold running water, or in the microwave.
- Divide large amounts of leftovers into shallow containers for quicker cooling in the refrigerator.
- Throw away perishable foods that have been left out at room temperature longer than 2 hours (1 hour if the temperature is over 90°F).
- When transporting food to a picnic, party, or potluck dinner, keep cold food cold by packing it in a cooler with ice or freezer packs. Hot food should be kept hot by wrapping it well and placing it in an insulated container.
- Place leftovers from the grill in the refrigerator within 2 hours.
So according to these guidelines, perishable foods like cheese should be refrigerated within 2 hours of being left out at room temperature. But what about a cheese like blue cheese that has special properties thanks to its mold cultures? Does the 2 hour rule still apply?
Factors That Impact How Long Blue Cheese Can Be Left Unrefrigerated
There are several factors that come into play when determining just how long blue cheese can safely be left out unrefrigerated before the risk of foodborne illness becomes too high:
- Type of blue cheese: The type of blue cheese makes a difference. Soft, creamy blue cheeses with higher moisture content like gorgonzola will perish faster unrefrigerated than harder, drier blue cheeses like Stilton. The more dense and firm the cheese, the longer it will take for potentially harmful bacteria to grow.
- Age of the cheese: Fully aged blue cheeses have lower moisture contents and higher salt contents than young cheeses, making them less hospitable environments for pathogens. Older blue cheeses can typically be left out longer than young soft blue cheeses.
- Shape/size of the cheese: A smaller piece of blue cheese will perish faster than a larger, solid block. A greater surface area exposed to air allows for faster moisture loss but also faster mold growth.
- Storage method: Was the cheese tightly wrapped and sealed? Or was it left sitting out loosely in the open air? An intact and properly wrapped block of cheese lasts longer unrefrigerated compared to cheese that has already been cut and rewrapped or left completely unwrapped.
- Environmental temperature & humidity: Warm environments above 40°F accelerate pathogen growth. Likewise, high humidity in the air also provides a more hospitable environment for mold and bacteria to thrive.
The interplay between all of these factors means that there is no black and white rule for how long blue cheese will stay safe at room temperature. The general guidelines suggest no more than 2 hours, but the specific characteristics of the cheese and the storage conditions make a big difference.
How Temperature Impacts Blue Cheese Safety
Temperature is one of the most important factors when determining how long blue cheese can safely be left unrefrigerated. Here is how ambient temperature impacts microbial growth on perishable foods like blue cheese:
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As you can see, the warmer the temperature, the faster bacteria (and mold) are able to proliferate. This is why perishable dairy products like blue cheese cannot be left out too long – even when refrigerated below 40°F, some bacterial growth still occurs.
Safe Time Limits for Unrefrigerated Blue Cheese
Taking into account the major factors of cheese type, age, shape/size, storage method, temperature, and humidity, here are some general guidelines for how long different types of blue cheese can safely be left unrefrigerated:
- Soft blue cheeses (like gorgonzola): no more than 1 hour, regardless of storage method
- Firm/hard blue cheeses (like Stilton):
- Whole solid block: up to 4 hours if tightly wrapped
- Cut/crumbled: 2 hours if covered
- Cut/crumbled: 1 hour if left uncovered
- Any blue cheese: no more than 30 minutes if temperature is above 90°F
The bottom line is that no blue cheese should be left out at room temperature for more than 4 hours total. To be extra safe, stick to the 2 hour rule, especially if the cheese has been exposed to air, is a soft type, or the temperature is warm.
How to Store Blue Cheese Properly
To safely store blue cheese for the longest possible shelf life, follow these tips:
- Keep refrigerated at 40°F or below at all times apart from brief periods left out for meal preparation and service.
- Wrap cheese blocks tightly in plastic wrap or wax paper. Minimize air exposure.
- Place cut/crumbled cheese in a sealed container or rewrap tightly in plastic wrap.
- Don’t let cheese contaminate other foods – keep in a designated cheese storage drawer away from ready-to-eat foods.
- Label cheese with date of purchase so you know when it’s expired.
- Use clean and dry utensils when handling cheese to prevent mold cross-contamination.
- Avoid temperature fluctuations – don’t repeatedly pull blue cheese in and out of the refrigerator.
With proper refrigeration and handling, most blue cheeses stay fresh for 2-4 weeks after purchase. Harder blue cheese wheels used for grating can last for several months.
What if a Little Mold Develops on the Cheese?
It’s common for additional mold to develop on the surface of blue cheeses over time. This is generally harmless. Simply use a clean knife to cut away a 1-inch layer around and below any surface mold. The cheese below should still be safe to eat if it has been continuously refrigerated at 40°F or less. Discard the unwanted moldy portion.
However, if the cheese has been left unrefrigerated long enough for pathogens like Listeria or Salmonella to grow, surface mold removal may not render it safe. When in doubt, remember the old adage – “When it mold, toss it out!”
Signs Blue Cheese Has Spoiled
Discard blue cheese immediately if you notice any of the following signs of spoilage:
- Cheese is dried out and crumbly
- Extreme mold growth (more than just surface mold)
- Cheese has an ammonia-like or rotten odor
- Cheese has a rancid flavor
- Cheese has a strange coloration or hue
- Significant sliminess
- Pink, black, or other discoloration from bacterial growth
Don’t taste blue cheese if you suspect it may be spoiled. Remember the cardinal rule – when in doubt, throw it out. Don’t risk getting sick from ingesting harmful molds and bacteria.
Can Spoiled Blue Cheese Make You Sick?
Eating spoiled, moldy blue cheese that contains high levels of bacterial toxins can cause symptoms of food poisoning including:
- Abdominal cramps
- Muscle aches
Symptoms may start within hours after ingestion and can last for several days until the toxins work their way out of your system. In severe cases, food poisoning from blue cheese can even be fatal.
Those most at risk include the very young, elderly, pregnant women, and those with compromised immune systems. Listeria infection from contaminated dairy products can be especially dangerous for pregnant women, potentially leading to miscarriage, stillbirth, or illness/death of the newborn.
Bottom line – don’t take risks with moldy blue cheese. Discard it as soon as you notice signs of spoilage.
Blue cheese requires refrigeration to remain safe to eat. While it can temporarily be left out at room temperature thanks to its low pH and special mold cultures, it should never go unrefrigerated for more than 4 hours, maximum. For soft types of blue cheese, 1-2 hours is the limit before safety becomes a concern.
To prevent foodborne illness, it’s essential to store blue cheese properly under 40°F refrigeration at all times. Follow the 2 hour rule as a good guideline for any periods where the cheese sits out during meal prep or snacking. When in doubt, err on the side of caution – you can’t go wrong storing cheese in the fridge or tossing it when signs of spoilage appear.
With proper handling, blue cheese can remain fresh for weeks, if not months, after purchase. But once contaminating molds and bacteria have taken hold, it’s best to say bye-bye to blue cheese rather than risk a bout of illness.