Mayonnaise is a popular condiment that can add flavor and moisture to sandwiches. However, there has long been a debate about whether mayo can be safely left on a sandwich overnight. The answer depends on several factors.
How Long Does Mayo Last?
According to the USDA, store-bought mayo has a recommended shelf life of around 3-4 months when stored unopened in the refrigerator. Once opened, mayo will generally last for about 2-3 months in the fridge.
These time frames are for mayo at optimal quality. The shelf life refers to how long the mayo retains its best flavor and texture when properly stored. The expired mayo doesn’t necessarily mean it has spoiled and become unsafe to eat. It means the quality has started to go down.
What Happens When Mayo Goes Bad?
As mayo ages and loses quality, a few changes happen:
- Texture becomes looser and may start separating
- Color darkens slightly
- Flavor becomes more bitter and unpleasant
- Smell turns rancid or rotten
These signs indicate the mayo is past its prime. Consuming spoiled mayo that has severely degraded in quality may cause stomach upset in some people due to the breakdown of fats and oils. But mild degradation of the mayo likely won’t make you sick.
Does Mayo Go Bad Faster on a Sandwich?
When used as a sandwich spread, mayo comes in contact with other ingredients like meat, cheese, veggies, and bread. This can potentially accelerate the spoilage process in a few ways:
- Bacteria from ingredients may contaminate the mayo
- Mayo may absorb moisture from veggies and bread
- Salty ingredients may disrupt the emulsion of oils and egg yolk
Close contact with other foods provides more opportunity for the quality of the mayo to break down. The USDA explains mayo has a typical shelf life of 2-3 days once on a sandwich or wrap.
How to Tell if Mayo Is Bad on a Sandwich
Here are some signs the mayo on your sandwich has spoiled and should be thrown out:
- Change in texture – Becomes very runny, watery, and separates
- Discoloration – Darker, dull, yellowish coloring
- Off smells – Sour, rancid, rotten odor
- Mold – Fuzzy texture or spots of mold
- Sliminess – Loses creaminess and becomes slimy
Trust your senses. If the mayo tastes or smells bad, looks odd, or has changed texture dramatically, play it safe and toss it.
Can You Leave Mayo on a Sandwich Overnight?
It’s generally not recommended to leave regular mayo out at room temperature on a sandwich overnight. The combination of the acidic mayo ingredients, moisture from the sandwich fillings, and warmth provide ideal conditions for bacterial growth. The USDA advises not leaving mayo-coated sandwiches out of refrigeration for more than 2 hours.
After sitting out overnight (about 8 hours or more), regular mayo has a high risk of developing bacteria that could make you sick. Some bacteria that can grow are:
- Salmonella
- Staphylococcus aureus
- Bacillus cereus
- Clostridium botulinum
- Campylobacter
Consuming contaminated mayo can then lead to food poisoning symptoms like nausea, vomiting, diarrhea, fever, and cramps anywhere from a few hours to a few days later.
Exceptions for Specialty Mayos
There are a few exceptions to the overnight mayo rule. Some specialty mayo products are formulated to be safer at room temperature for longer than regular mayo:
- Mayo with lemon juice – The extra acidity helps inhibit bacterial growth.
- Mayo with added garlic or herbs – Natural antimicrobial compounds prolong shelf life.
- Vegan mayo – No raw eggs means lower contamination risk.
- Commercial light mayo – More vinegar and less egg create an unfavorable pH for many bacteria.
Check labels on specialty mayo products to see if they can be kept unrefrigerated before leaving them out. When in doubt, it’s far safer to throw out the sandwich instead of risking illness from bad mayo.
Other Tips for Handling Mayo
Here are some other mayo safety recommendations:
- Keep unopened mayo bottles refrigerated at 40°F or below.
- Throw out mayo 2-3 months after opening.
- Use clean utensils each time you take mayo from the jar.
- Don’t mix new and old mayo in the same container.
- Refrigerate sandwiches with mayo right after assembly.
- Don’t let mayo-coated sandwiches sit out for more than 2 hours.
Following proper storage and handling guidelines helps keep mayo safe and extends its shelf life.
Can You Eat a Sandwich with Bad Mayo?
It’s generally best to throw out any sandwich that contains mayo with obvious signs of spoilage like changes in texture, smell, taste or appearance. The small risk of food poisoning usually isn’t worth it.
However, if the mayo just seems a little bit off but not completely rancid or moldy, you can try scraping it off. Removing the iffy mayo eliminates the source of potential bacteria or toxins. Fresh mayo can then be reapplied to the sandwich.
As always, it’s important to thoroughly cook meats like chicken, beef or sausage to destroy any bacteria. Proper cooking temperatures can kill pathogens and make the overall sandwich safer, even if the mayo is borderline.
Conclusion
Leaving regular mayonnaise out on a sandwich at room temperature overnight is risky business and provides prime conditions for multiplying bacteria. For food safety, sandwiches with mayo should be refrigerated within 2 hours of assembly.
Specialty mayos formulated to resist bacterial growth may last a bit longer unrefrigerated, but it’s still best practice to err on the side of caution. When in doubt, toss it out. Checking for signs of spoiled mayo and reheating meats can reduce but not eliminate the risk. Overall, leftovers containing mayo are safest when promptly refrigerated.
Key Takeaways
- Regular mayo can go bad within 2-3 days on a sandwich due to ingredient interaction.
- Leaving mayo out overnight can lead to food poisoning from bacterial growth.
- Discard sandwiches if the mayo smells, looks, or feels off.
- Some specialty mayos last longer unrefrigerated, but it’s still ideal to refrigerate.
- Thoroughly cooking meats and removing bad mayo reduces risk of illness.
References
[1] U.S. Department of Agriculture Food Safety and Inspection Service. “M Miracle Whip and Mayo.” https://www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/food-safety-basics/miracle-whip-mayo
[2] U.S. Department of Agriculture Food Safety and Inspection Service. “Refrigerate Promptly.” https://www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/food-safety-basics/refrigerate-promptly
[3] Centers for Disease Control and Prevention. “Food Poisoning.” https://www.cdc.gov/foodsafety/food-poisoning.html
[4] U.S. Food and Drug Administration. “Key Facts on Keeping Foods Safe.” https://www.fda.gov/consumers/consumer-updates/4-key-facts-keeping-foods-safe