What’s Up with Condiments?

Whether it’s ketchup and mustard on a burger or mayonnaise used in a favorite potato salad, do condiments need to be stored in the refrigerator?  Looking at the container for your favorite sauce or condiment, you will almost always find the words Refrigerate after Opening.  My own home refrigerator has over a dozen such bottles: barbecue sauces, salad dressings, mayonnaise, mustard, hot sauces, and more – all labeled Refrigerate after Opening.  But when camping away from home where refrigeration is not available, or if you forget and leave the ketchup on the counter overnight, do condiments present a food safety risk if not refrigerated?  Well…the answer may surprise you!

Research done at the University of Wisconsin-Madison has shed light on this question.  In the first study, researchers took standard grocery store ketchup, mustard, and sweet pickle relish, opened the containers, added Salmonella or E. coli  O157:H7 and then either refrigerated the containers (40°F) or placed the inoculated containers at room temperature (73°F), and checked over time to see if the pathogens would grow.  The pH of the samples averaged 3.6, 3.1, and 2.8 for the ketchup, mustard, and sweet pickle relish, respectively (pH is a measure of acidity and foods with a pH of 4.6 or below are considered high in acid).

What were the results?

  • Pathogens survived longest in ketchup; the product with the highest pH and lowest acidity.
  • All Salmonella died within 1 hour in the mustard and sweet pickle relish stored in either the refrigerator or at room temperature.
  • All Salmonella died within 1 day in ketchup at room temperature, or within 2 days in the refrigerator.  E. coli 157:H7 died off within 2 days at room temperature and within 7 days in the refrigerator.

A subsequent review of the microbiological safety of common condiments indicated that typical mayonnaise has a pH of 3.7, suggesting that results would be similar to findings with ketchup.

What does this mean for home-storage of condiments?  Condiments like ketchup, mustard, mayonnaise, and pickles should be stored in the refrigerator for quality.  These products, once opened, will maintain quality better if stored in the refrigerator and that is the primary reason that package instructions indicate refrigerate after opening.  However, if you forget and don’t refrigerate condiments over a weekend camping trip or leave the ketchup beside the refrigerator overnight, this should not present a food safety concern as long as the condiments did not become contaminated, perhaps from a meat-basting brush that touched raw meat or chicken or a from a knife that touched raw meat or was licked clean.

Best practice for handling condiments.  Follow these best practices when handling kitchen staples like salad dressing, mustard, mayonnaise, ketchup and pickles:

  • Refrigerate after opening for quality.  If you forget and leave items out overnight, don’t panic.  As long as you didn’t contaminate the product, the acid will help ensure safety; simply transfer items to the refrigerator as soon as possible.
  • Avoid contaminating condiments with meat or poultry juices, or even human germs.  While we expect the acidity of condiments to help ensure safety, it could be possible to transfer so many germs to the container that the amount of acid simply was not enough and pathogens survived.
  • Avoid condiments such as mayonnaise or mustard made with raw eggs (homemade items).  Commercial products contain pasteurized eggs that help ensure safety.

Stay well and food-safe.


Tsai and Ingham. 1997. Survival of Escherichia coli O157:H7  and Salmonella spp. in acidic condiments. Journal of Food Protection. Volume 60, pages 751-755.

Smittle. 2000. Microbiologial safety of mayonnaise, salad dressings and sauces produced in the United States: a review. Journal of Food Protection. Volume 63, pages 1144-1153.

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Authored by: Barb Ingham