Signs of Spoilage in Home Canned Food

Signs of Spoilage in Home Canned Food

When preserved correctly, homemade canned foods won't go bad, ever. But realistically speaking, the food can last for at least two to five years easily without compromising on the taste or nutritional value.

And also when preserved correctly, the chance of the food in the jar spoiling is minimal, but it can happen.

Spoilage occurs when there's a disagreeable change in the normal state of the food. It's usually caused by bacteria, molds or yeasts.

Free Printable Pressure Canning Steps in PDF

Generally, spoilage occurs for three main reasons:

• Inadequate heat during processing which allows the survival and growth of mesophilic microorganisms.
  
  
  
• Inadequate cooling after heating or high-temperature storage allows germination and growth of thermophilic spores.
  
  
  
• Leakage contamination after processing.
  
  

Even jars that look fine on the outside might have contaminated food inside, so inspecting each jar upon opening is important.

Here are most common signs of spoilage to look for when you open up a home canned jar of food. If you experience any of the following things, you should THROW IT OUT.

An Unsealed Jar

This is the most common scenario. The lid has become unsealed in storage. A false seal can occur when the product is not canned appropriately.

Examples of mistakes made during processing that may cause the jar to unseal or have a false seal.

• Jar rims were not wiped clean before processing.
  
  
• Jars were not filled correctly. 
  
  
•  Proper headspace recommendation was not adhered to.  
  
  
• Product was not heat processed for the appropriate amount of time.

Bulging Lids

A buckling or bulging lid occurs when air that's trapped in the headspace between the bottom of the lid and the top of the food is not forced out of the jar in processing as it should be. 

When lids are on too tight, the air cannot easily escape so it forces its way out by deforming the lid. 

Spurting Liquid When Jar is Opened

This is an indication that the food is under pressure from bacteria activity.  A sure sign of spoilage.  

Active Bubbling

Active bubbling means that bubbles are actively moving upwards in the jar. This can be confusing as it's natural to see active bubbles when you first process the jars and for a few days later as the food cools and settles. Again, this is normal.

But if you open a jar that has been stored for weeks or months and see active bubbles moving upwards, that's a sure sign that the product may be fermenting or contaminated.  

Mold, Scum, Film on Top of the Food

If good equipment and proper technique were used, it is unlikely you will ever have mold growth in your unopened canned goods.

If you do have such a problem, that's a sign that there was either a flaw in the procedure you used, or something affected the jar after the fact to break its seal.  

Unnatural-Looking Colors or Textures

Food looks cloudy.

Cloudy brine inside the jar is a sign that bacteria are starting to grow.


Food Looks Soft, Mushy

An indication that the food has bacteria spoilage.

Disagreeable Odor

"Flat Sour"


Flat sour is an unappealing off-flavor in canned goods that is caused by thermoduric microorganisms which survive the canning process.  The off-flavor is produced by such fermentation.

Give every opened jar the smell test.

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Checking the Seal Before Storage

As long as your jar completely sealed, your food should remain safe to eat. You can check the seal after processing and after the jar cools by removing the ring and elevating the jar holding onto the lid. A good seal means that it will hold fast.

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Home canning is an excellent way to preserve garden produce or take advantage of great sales at the market.  It's also a great step toward self sufficiency. 

It continues to be a safe endeavor as long as processing rules are followed and careful inspection of the food is done before eating.

Other Canning Articles:

15 Common Questions Answered About Canning

Pressure Canning Check List of Items Needed  Printable

List of Items Not Safe to Can

The Role of Vinegar in Canning

The Importance of Headspace in Canning

Signs of Spoilage in Home Canned Foods

Prep for Making Fruit Jellies and Five Steps to Waterbathing

Why Canning Jars Break

Reasons for Loss of Liquid in Canning - Siphoning

Canning Jar Sizes and Their Uses

Reasons Canning Jars and Contents Darken

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