How long should a jar of mayonnaise be kept once it’s been opened?

Kraft recommends that opened, refrigerated mayonnaise be discarded after  3 – 4 months (or 30 days after the expiration date if that comes sooner). The USDA says 2 months after opening. (The  USDA’s recommendation refers to all brands; different brands contain somewhat different ingredients, for example, different levels of acidity.) Take your pick since this advice is based upon loss of quality not safety. After a few months, the color and/or flavor may deteriorate, but the mayonnaise will generally be safe to consume if your refrigerator temperature is at or below 40°F. 
It’s a good idea to write  on the label the date you open the jar so that you’ll know when the quality is beginning to deteriorate. 
Kraft Foods recorded customer service phone message “Surprising Expiration Dates”
USDA Food Safety and Inspection Service


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