It has happened to most of us at least once: we open the refrigerator door and take something out, only for our eyes to fall on a jar of mayonnaise nestled away in the back. Because we only use a little bit at a time, a jar of mayo can go unnoticed in the fridge for weeks or even months. Fortunately, even if it's been there for some time, your mayonnaise is probably still good to eat.
Opened jars of mayonnaise should be kept in the refrigerator. If kept refrigerated, a jar should last for around two months. However, chances are good that mayonnaise that has been kept continually refrigerated should last even longer. The "best before" dates given on food packaging in the U.S. refer to quality rather than safety. After a few months, the mayonnaise may begin to lose its fresh flavor or change consistency. You might not want to eat it or cook with it, but it's still unlikely to be harmful.
Many people worry about mayonnaise going bad because they've heard horror stories about expired mayonnaise causing salmonellosis, a type of food poisoning caused by salmonella bacteria. Although salmonella is a serious illness that can cause painful cramps, fever and diarrhea, commercial mayonnaise is unlikely to cause salmonella poisoning. Mayo's high acidity makes it a poor breeding ground for bacteria. In fact, commercial mayonnaise is safe even if stored at room temperature--although it may lose its consistency.
Preservation Without Preservatives
Of course, not all mayonnaise is purchased from a store. Homemade mayonnaise is simple to make, inexpensive and delicious, but it doesn't last nearly as long as its commercial counterpart. A jar of homemade mayonnaise should be kept in the fridge for only a few days to a week. Homemade mayonnaise lacks the preservatives that keep commercial mayo stable for months. Additionally, it may not have the acidity needed to limit bacterial growth.
Although mayonnaise is generally safe when refrigerated, a little caution is always a good thing when dealing with food safety. If your mayo smells funny or has developed mold, ignore the date on the jar and just get rid of it. If your mayonnaise has been out of the refrigerator at 50 degrees Fahrenheit (10 degrees Celsius) or higher for eight hours or more, the U.S. Department of Agriculture recommends disposing of it.
- Food Marketing Institute: Foodkeeper -- Mayonnaise
- North Dakota State University: Prairie Fare -- Is Mayonnaise Really a Food Safety Issue?
- Centers for Disease Control and Prevention: Salmonella
- West Virginia Department of Agriculture: Mayonnaise -- The Misunderstood Dressing
- BBC: Homemade Mayonnaise
- Bon Appetit: Is Homemade Mayonnaise Worth the Effort?
- Still Tasty: Mayonnaise, Commercially Bottled -- Opened
- FoodSafety: Refrigerated Food and Power Outages -- When to Save and When to Throw Out
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