How long can mayonnaise be kept unrefrigerated?

In this brief guide, we will answer ‘how long can mayonnaise be kept unrefrigerated?’ Also, we will look into why can’t mayonnaise be stored in the pantry and how you should properly store it.

How long can mayonnaise be kept unrefrigerated?

You can keep your open jar of mayonnaise sitting out at room temperature for up to 8 hours, based on USDA guidelines. An opened jar that has been held above 50 degrees F for more than 8 hours should be immediately discarded (1).

While, an opened jar of mayonnaise that has been continuously refrigerated, will generally maintain the best quality for 2 to 3 months even after the ‘best by’ date on the package.

What makes mayonnaise perishable?

Mayonnaise is made from raw eggs, 65% vegetable oil, vinegar, lemon juice and some stabilizers, based on US Food & Drug Administration. Since the majority of the mayonnaise is oil and raw eggs it makes mayonnaise fall under perishable food items.

Despite this, mayonnaise has raw eggs in it therefore, it carries a slight risk of salmonella too. However, food manufacturers are now actively using pasteurized eggs in their mayonnaise to eliminate the cause of this slight risk too. Acids to diminish pH value and essential plant oils as natural preservatives are also used to increase shelf life of products (2).

Most mayonnaise brands add stabilizers and other ingredients like natural preservers or acids which inhibit bacterial growth and make their jar or pouch shelf-stable until the said jar or pouch is unopened. The presence of air dramatically increases the oxidation rate of mayonnaise lipids. Therefore,But the moment you break the seal of your jar or pouch it’s best to store it in the fridge since bacteria grow rapidly at temperatures between 40°F and 140 °F. It will stay safe for 2 to 4 months in the fridge. But if you have a jar or pouch that has been in your fridge for at least a year it’s best to throw it out (2).

Because the FDA has marked mayonnaise as a perishable food item it is best to throw out the mayonnaise that has been left out of the fridge overnight, if you don’t want to get yourself sick or end up with food poisoning (1).

Is mayonnaise a potential source of foodborne illness?

No. Despite being made of raw eggs, mayonnaise is still not a source of any foodborne illness only if the said mayonnaise was stored in the fridge. Not if your mayonnaise was left out, unrefrigerated and unprotected then it ‘may’ become a source of foodborne illness.

The reason behind this is that when perishable foods are left out there is a high chance that bacteria starts to rapidly multiply and produce toxins that can result in diarrhea, vomiting, nausea or food poisoning. The reason for that, is that mayonnaise is made of raw eggs and is a strong candidate for Salmonellosis outbreaks, the food infection caused by Salmonella. Even though several food items like peanuts, beef, pork, and chicken have been connected with the outbreaks of salmonellosis, eggs and food products prepared using eggs seem to be the most frequent foods that are involved with the disease (3).

How long does mayonnaise last under different conditions?

Storage conditions are critical to determine the storage time of unopened commercial mayonnaise. At room temperature conditions (20 °C), unopened mayonnaise jars can be consumed one year after its manufacturing date. But, when exposed to sunlight, even for a short period of storage, the product can be rancid in six months or less (2) . Once opened, the mayonnaise will be exposed to air and that increases dramatically the oxidation rate of the lipids. The ingredients also play an important role in shelf life and many manufacturers use natural antioxidant ingredients, like mustard and herbs, to extend storage time (2). The following chart briefly explains how long your mayonnaise will be safe to consume under the following conditions;

 PantryRefrigerator
Unopened jar of mayonnaise3 to 4 months even after its ‘best before’ dateUp to a year
Opened jar of mayonnaiseNot more than 2 hours2 to 4 months

How should you store home-made mayonnaise?

We have discussed store-bought and commercially available mayonnaise but what about homemade ones? No worries we have got you covered over it as well. Salmonellosis is one of the main causes of foodborne illnesses worldwide, with outbreaks predominantly linked to contamination of eggs and raw egg products, such as mayonnaise. The ingredients chosen to formulate the mayonnaise are important to determine the shelf life of the product (3).

Just like other commercial and store-bought mayonnaise, homemade mayonnaise is also made with raw eggs, vegetable oil and any other acid like vinegar or lemon juice. But the ratio of acid in homemade mayonnaise does not assure proper long-lasting quality. The addition of plant herbs could extend shelf life of mayonnaise. Plant essential oils are well-known as antibacterial agents that could be used to control foodborne diseases. Some examples are mint, cinnamon, cardamom, oregano, garlic and clove (3). 

The addition of salt is also important to preserve mayonnaise. The sodium ions associate with water molecules to reduce the amount of unbound water in foods, making it difficult for the microorganisms to grow (3).

Therefore, homemade batches are often prescribed to be either used immediately after it is made or be stored in an airtight jar in the refrigerators. You can store your homemade jars for no more than 5 days. Once the 5 day period is up, it is best to discard it.

How to tell if your mayonnaise has gone bad?

Just like any other food item, visual appearance, smell and taste play a major role in telling whether your food is spoiled yet or not. Low pH and high fat content of mayonnaise makes it more resistant to microbial spoilage, but not free from them. Added to that, one should be aware of lipid oxidation, which can cause rancid aroma (4).

Textural changes

Mayo has a thick consistency but when the bacterial load has gone up you may notice your mayonnaise separating and liquid gathering up, it is best to chuck it out.

Discolouration

Mayo is creamy white in color but when the mayo goes bad the color may vary from yellow to brown. Such mayo is not safe and should be discarded.

Strange smell

Mayo has little to no fragrance to it, but when it starts to smell acidic or putrid it’s best to throw it out. Mayonnaise is susceptible to deterioration due to auto oxidation of the unsaturated fats in the oil. This process leads to the formation of aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids and epoxy compounds known as secondary oxidation products, which are responsible for the off-flavor and off-odor of the oil (4).

Sour taste

Mayonnaise is susceptible to oxidation resulting in quality deterioration and the formation of undesirable components such as free radicals and reactive aldehydes, which can cause rancid flavor (4). Mayo doesn’t change its taste until it has gone bad. So if you have suspicions that your mayo has gone bad a little bit, if it tastes sour or pungent it is best to throw it out.

Other FAQs about Mayonnaise that you may be interested in.

Why doesn’t mayonnaise have protein?

Why is mayonnaise white?

What is the difference between mayo and mayonnaise?

Conclusion

In this brief guide, we answered ‘how long can mayonnaise be kept unrefrigerated?’ Also, we will look into why can’t mayonnaise be stored in the pantry and how you should properly store it.

Hopefully, you found this helpful and informative. If you have any other queries or comments, please do let us know.

Citation

  1. Keeping Food Safe During an Emergency. Food Safety and Inspection Service. US Department of Agriculture. 2013.
  2. Lagunes‐Galvez, L. A. U. R. A., et al. Oxidative stability of some mayonnaise formulations during storage and daylight irradiation. J Food Lipids, 2002, 9, 211-224.
  3. Keerthirathne, Thilini Piushani, et al. A review of temperature, pH, and other factors that influence the survival of Salmonella in mayonnaise and other raw egg products. Pathogens. 2016, 5, 63.
  4. Gorji, Sara Ghorbani, et al. Lipid oxidation in mayonnaise and the role of natural antioxidants: a review. Trends Food Sci Technol, 2016, 56, 88-102.