Quick Answer
Mayonnaise can go bad within 2-3 hours if left out at room temperature. The USDA recommends discarding mayo that has been left out for more than 2 hours above 50°F. Mayonnaise contains egg yolks, oil, and vinegar or lemon juice. The egg yolks provide an ideal environment for bacterial growth, so mayo must be kept refrigerated. Leaving mayo unrefrigerated for too long allows bacteria to multiply quickly, causing the mayo to spoil.
How Mayonnaise Spoils
Mayonnaise is an emulsion of egg yolk, oil, and an acid like vinegar or lemon juice. It also usually contains seasonings and stabilizing ingredients like salt, mustard, and sugar.
Role of Ingredients in Spoilage
Egg Yolks
Raw egg yolks contain many nutrients that bacteria need to grow. Salmonella and E. coli are two hazardous bacteria that can be found in raw eggs. The acidic environment of mayonnaise helps control bacterial growth, but does not prevent it completely.
Oil
The vegetable oil used in mayo provides a moist environment ideal for bacterial multiplication. Oils are able to transfer oxygen from the air into the mayo, allowing aerobic bacteria to thrive.
Vinegar or Lemon Juice
Vinegar and lemon juice give mayonnaise its acidic pH, which helps limit bacterial growth. However, the acidic pH is not low enough to completely prevent spoilage microorganisms.
Other Ingredients
Spices, salts, and sugars contribute additional nutrients for bacteria. Stabilizers like xanthan gum also provide suitable conditions for bacterial growth.
Signs of Spoiled Mayonnaise
As bacteria multiply in the mayo, they produce gases and unpleasant metabolites that alter the texture, smell, and taste:
Texture
– Becomes more thin and watery
– Loses thickness and creaminess
– Develops dark watery spots
Smell
– Strong unpleasant sour odor
– Rotten egg smell from hydrogen sulfide gas
Taste
– Sharp, vinegar-like taste
– Bitter taste
Appearance
– Darkening in color
– Watery liquid oozing out
– Gas bubbles
– Green, blue, pink, yellow discoloration from bacterial pigments
So if your mayo becomes excessively runny, changes color, smells bad, or tastes off, it has likely spoiled and should be discarded.
How Long Does Mayo Last Unrefrigerated?
The shelf life of mayonnaise depends on several key factors:
Ingredients
Homemade mayo without preservatives spoils faster than commercially prepared mayo containing preservatives and stabilizers.
Storage Temperature
Higher room temperatures allow bacteria to grow and multiply faster. Mayo lasts longer when kept cool.
Acidity
Mayo with more vinegar or lemon juice can last slightly longer thanks to the acidic pH inhibiting bacterial growth.
Container
Opened jars of mayo spoil faster than unopened jars since they are continually re-exposed to air and contaminants.
Given these factors, most experts agree:
Unopened Mayo:
– Lasts 2-3 months past the “best by” date if kept refrigerated
– Lasts 4-6 hours out on the counter before spoiling
Opened Mayo:
– Lasts 2-3 months refrigerated
– Lasts just 2-3 hours unrefrigerated before bacteria become dangerous
So once opened, mayonnaise should always be refrigerated. Discard any leftovers if mayo has been left out more than 2 hours.
How to Tell If Mayo Is Bad After Being Left Out
Here are some simple ways to check if your mayo is still safe or has spoiled after sitting unrefrigerated:
Smell It
Fresh mayo has a rich, creamy smell. If it smells sour or unpleasant, it has likely spoiled.
Inspect Consistency
Mayo loses thickness and becomes watery when contaminated by bacteria. Spoiled mayo may also have an unnatural color.
Taste a Small Amount
If the flavor is very acidic, bitter, or just “off”, the mayo is no longer good.
Check the Color
Mayo turns gray, yellow, or pink when aged. Changes in color can signal spoilage.
Look for Gas Bubbles
Gas pockets, foaming, or bubbling means bacteria have been actively growing in the mayo.
Note the Temperature
If the jar feels warm or hot, that’s a sign of advanced bacterial multiplication. Toss it.
When in Doubt, Throw It Out
It’s not worth risking your health to try to save a spoiled batch of mayonnaise.
How to Store Mayo to Prevent Spoilage
To maximize freshness and prevent mayonnaise from spoiling too quickly, be sure to:
Refrigerate after Opening
Keep all opened mayo jars in the fridge at 40°F or below.
Use Clean Utensils
Always use a clean knife or spoon to avoid introducing bacteria.
Minimize Air Exposure
Limit how much the mayo gets exposed to air during use by scooping out only what you need.
Check “Best By” Dates
Don’t use mayonnaise past the “best by” or expiration dates on the jar.
Store Upside Down
Inverting opened jars helps block air contact and keeps the mayo fresher longer.
Seal Tightly
Always screw lids back on tightly and store opened mayo towards the back of the refrigerator.
Keep Refrigerator Cold
Maintain your fridge temperature at 40°F or below. Cold temps slow bacteria growth.
Following proper storage methods and food handling practices can help prevent mayonnaise from spoiling prematurely.
Can You Freeze Mayo to Make it Last Longer?
Freezing is not recommended for mayonnaise for a few reasons:
Texture Changes
Freezing and thawing mayo causes it to separate and become watery. The emulsified texture breaks down.
Flavour Loss
The flavor of mayo diminishes significantly after freezing. It tastes bland after thawing.
Bacterial Growth
Bacteria and molds can still grow, even at freezer temperatures. Freezing does not kill microbes.
Frostburn
Freezing mayo in the jar can cause frostburn around the rim. This leads to off-flavors.
Weeping Liquid
Thawed mayonnaise often weeps liquid, making it unusable. The emulsion doesn’t re-form well.
While commercially prepared shelf-stable mayo can be frozen, it’s best to avoid freezing homemade or opened mayonnaise. Refrigerating and using opened mayo within 2 months is better. Discard if you see any signs of spoilage.
Can You Reverse Spoiled Mayo?
Unfortunately, there is no reliable way to reverse mayo spoilage. Once bacteria have multiplied and produced off-flavors, gases, and sliminess, the only safe option is to discard the mayonnaise.
Heating or Cooking
Heating spoiled mayo is not recommended, as it does not kill all harmful bacterial toxins or waste products.
Adding Acid
Extra lemon juice or vinegar may mask sour tastes slightly but cannot restore spoiled mayo to an edible state.
Mixing in Fresh Mayo
Diluting spoiled mayo with new mayo can spread bacteria throughout the whole batch and give false confidence in eating a risky product.
Using Preservatives
By the time mayo shows signs of spoilage, it is too late for preservatives to work effectively.
Straining the Mayo
Straining or filtering separates out some microbes, but many remain, along with their toxic metabolites.
When mayonnaise smells bad, changes texture, or shows signs of contamination, it’s best to discard it fully. The small amount saved is simply not worth risking foodborne illness.
How Long Does Mayonnaise Last in the Fridge?
Properly stored mayonnaise can maintain top quality and fresh taste for 2-3 months in the refrigerator.
Unopened Mayo
Store-bought mayo sealed in an airtight container lasts up to:
– 3-4 months past the “best by” date.
– 6-8 months total from the manufacturing date.
Opened Mayo
After opening, mayonnaise lasts:
– 2-3 months in the fridge.
– Keep refrigerated at all times and make sure lid seals tightly.
Homemade Mayo
Lasts 1-2 months refrigerated.
– Homemade mayo without preservatives spoils fastest.
– Discard if you see any mold or textural changes.
Commercial Mayo
Mass-produced mayo keeps slightly longer thanks to added preservatives and stabilizers.
– Unopened, lasts 4-6 months past the “best by” date.
– Opened, lasts around 3 months refrigerated.
So sticking to the recommended storage times, keeping lids sealed, and refrigerating after opening allows mayonnaise to retain safe freshness for months before it goes bad.
Lasting Tips for Mayo
Here are some final tips for maximizing the shelf life of your mayonnaise:
– Check expiration or “best by” dates and don’t use mayo past them.
– Keep unopened mayo in a cool, dry pantry away from direct sunlight.
– Refrigerate opened mayo jars at 40°F or colder.
– Use clean utensils to avoid introducing bacteria.
– Limit air exposure by scooping out only what you need each use.
– Store opened mayo upside down to block air contact.
– Freeze only commercially shelf-stable mayo, not homemade or opened jars.
– Discard immediately if mayo smells, tastes, or looks abnormal. Don’t take risks!
– Make and use smaller batches of fresh homemade mayo to reduce spoilage waste.
– When in doubt, throw it out! Don’t taste test questionable mayonnaise.
Following proper refrigeration and food safety practices allows you to enjoy the convenience, flavor, and versatility of mayonnaise for months past the use by date with minimal risk of food poisoning. But once open, always refrigerate mayo and toss leftovers after 2-3 months.
Conclusion
Mayonnaise can spoil rapidly if left unrefrigerated, with most experts recommending it be discarded if left out more than 2 hours at room temperature. Bacteria multiply quickly in the egg yolks, oil, and moist ingredients in mayo. Refrigeration at 40°F or below is critical for slowing bacterial growth and keeping mayonnaise safe and shelf-stable for longer. Discard any mayo that smells odd, changes texture, or shows signs of spoilage like bubbling or discoloration. While freezing can prolong shelf life of unopened commercial mayonnaise, it’s not recommended for homemade or opened mayo. Following proper storage methods, checking expiration dates, and using clean kitchen practices allows you to safely keep mayonnaise for months opened or unopened. But when in doubt, throw it out – getting sick from spoiled mayonnaise is never worth the risk.
