Does Mayonnaise Expire?
Yes, mayonnaise can expire. Unopened mayonnaise lasts 3-4 months past the printed date. Once opened, it should be used within 2-3 months when refrigerated. Unlike popular belief, commercial mayo is quite stable due to acidic ingredients, but it will eventually spoil.
Key Takeaways
- Commercial mayonnaise is more shelf-stable than homemade because it contains vinegar or lemon juice that lowers pH and prevents bacterial growth.
- Homemade mayonnaise with raw eggs has a much shorter shelf life (about 1 week refrigerated).
- Mayonnaise left out at picnics is often blamed for foodborne illness, but usually the other ingredients (chicken, potatoes) are the culprits.
Explanation
Commercial mayonnaise is more shelf-stable than homemade because it contains vinegar or lemon juice that lowers pH and prevents bacterial growth. The eggs in commercial mayo are also pasteurized. Unopened jars are remarkably stable.
After opening, mayonnaise should always be refrigerated. It can actually last quite a while in the fridge because of its acidic nature. The two-month guideline is conservative; properly stored mayo often stays good longer.
Signs of spoiled mayonnaise include off or sour odors, yellowing or darkening color, separation that does not remix when stirred, and any visible mold. When in doubt, discard it - the risk is not worth saving a few dollars.
Commercial mayonnaise typically has a pH between 3.6 and 4.0, which is acidic enough to inhibit the growth of Salmonella, E. coli, and most other foodborne pathogens. This is why the FDA does not require commercial mayo to be refrigerated before opening, and why unopened jars can sit on store shelves for months. The real danger with mayo-based dishes like potato salad or tuna salad at picnics comes from the other ingredients raising the overall pH into the danger zone (above 4.6), where bacteria can multiply rapidly at temperatures between 40-140 degrees Fahrenheit.
Squeeze bottles keep mayonnaise fresher than jars because the narrow opening limits air and contaminant exposure. Every time you dip a knife or spoon into a jar, you introduce bacteria and food particles that accelerate spoilage. If you use mayo from a jar, always use a clean utensil and never double-dip after it has touched bread, meat, or other foods. Japanese Kewpie mayonnaise, which uses only egg yolks instead of whole eggs and includes MSG for umami flavor, has a similar shelf life to American-style mayo but should follow the same storage rules once opened.
Things to Know
- Homemade mayonnaise with raw eggs has a much shorter shelf life (about 1 week refrigerated).
- Mayonnaise left out at picnics is often blamed for foodborne illness, but usually the other ingredients (chicken, potatoes) are the culprits.
- Reduced-fat mayonnaise may have shorter shelf life than full-fat versions.
- Single-serve mayonnaise packets (like those from fast food restaurants) can last 6-8 months unopened at room temperature due to their hermetically sealed, oxygen-free packaging, making them more stable than an opened jar in your fridge.