A false seal is one of the most common problems when canning food.
Typically a false seal will occur when the right recipe or canning process is not followed.
Canning is a science.
You must follow the guidelines to a ‘T’ to ensure that the canned food is safe and can be stored for a long period.
Not following the right recipe and canning process increases your risk of getting sick and spoiling the food.
This guide will explain the causes of false seals and how to prevent them since any opening from a false seal can cause bacteria and other microorganisms to grow in the jars.
What is a False Seal?
A false seal occurs when the lid of the jar breaks or opens.
False seals are a sign that a vital step in the canning process was missed. Common reasons for false seals are:
- Overfilling the jars
- Miscalculating the processing time
- Not watching the processing temperature
A false seal is one of the worst things that can happen when canning since it is a sign that the canned food is not edible. Canned food that has been exposed to airborne microorganisms can lead to food-borne illnesses such as botulism.
So if a jar has a false seal then it needs to be resealed immediately before being stored long term.
5 Common Causes of False Seals
Here are the 5 most common reasons for false seals when canning.
1. Over or Underfilling the Jar
Incorrect filling means there will be an incorrect amount of headspace.
Headspace refers to the space between the filling (food) and the lid.
The ideal headspace is 0.5 inch between the top layer of your filling and the lid for the perfect vacuum seal.
Leaving not enough headspace or putting too much food into the jar will lead to siphoning. Siphoning is where the food will spill out and the jar will not seal.
Leaving too much headspace or not putting enough food in the jar will cause air to get trapped in the jar. This air prevents the jar from forming a vacuum seal when processing.
So make sure to leave 0.5 inch of headspace when canning.
2. Dirty Jar Rims
If the rims of the jars are dirty then the jar will not be able to create a vacuum seal.
An important step to canning is to wipe the jar rims. This step is easy to skip if the filled jars look clean.
However, oil and fat may rise to the rim which creates a dirty surface that will not create a clean seal.
So always wipe the jar rims before canning.
3. Incorrect Processing Time and Temperature
Canning is a science which means the processing time and temperature must be followed precisely.
The challenge with canning is that altitude does affect the canning process. So if you live at a higher elevation such as Denver, Colorado then you need to adjust the temperature to create a seal.
Another temperature challenge with canning is not heat-processing the lids and jars.
When you pour hot food into unprocessed jars and cover with cold lids (open kettle canning), the chance of false sealing increases. Open kettle canning is deemed unsafe and not recommended for food preservation.
4. Low Quality Jars and Lids
Low quality jars and lids will increase the chances of a false seal.
Low quality jars will break or crack easily when heat-processed. Most low quality jars will crack along the rim when vacuum sealing, which creates a false seal. So always inspect the jars before and after canning to make sure the jar is not compromised.
Canning lids are meant to only be used once for canning so make sure to use new lids when canning. Do not reuse old lids as this increases the chances of a false seal being created.
Another cause of false sealing is the jar size.
Most recipes call for specific jar sizes so using a larger jar than the recommended size will change the processing temperature and time to create a good seal.
If you use a different size jar than the recipe then you risk increasing the chance of a false seal being created unless you know the correct processing time and temperature for that jar size.
5. Testing the Seal Before the Jar has Cooled
It may be tempting to retighten the jar after removing it from the canner. However, trying to tighten the jar after canning is the worst thing to do since the hot lid can pierce the gasket and open the seal.
Processed jars need at least 24 hours for cooling before being placed in storage.
If you test the canned jars before they cool then you may create a false seal and expose your food.
Are False Seals Bad?
A false seal exposes your processed food to airborne microorganisms such as fungal spores. Eating food with these spores increases your risk of getting botulism and other food-related illnesses.
So false seals must be avoided at all costs.
Steps To Follow After Finding A False Seal
Once you find a false seal, the jar needs to be reprocessed otherwise the food will spoil. However, reprocessing the jar will only work if the jar has been unsealed for less than 24 hours.
If you discover the canned jar has a false seal after storing it for a few days, weeks, or months then the food is not safe to consume. It’s best to discard any jars that have a false seal in storage.
The following steps should only be followed if you find the jar unsealed within 24 hours of canning.
Reprocessing Jars with False Seals
- Examine the jar.
- Remove the lid and check the rim of the jar for any cracks. If you notice any cracks, then pour the food into a new jar.
- Check if there are food deposits or grease on the rim or lid. Wipe the jar’s rim with a clean cloth.
- Reprocess and label the jar as “re-canned”. Alternatively, you can store the jar in the refrigerator and consume the food within 3 days.
Remember, you can only reprocess a jar with a false seal as long as the seal came off within 24 hours of canning.
Tips For Preventing a False Seal
Here are 6 tips that will help prevent a false seal from ever being created.
1. Remove Air Bubbles
A common mistake among beginners is not removing air bubbles from the food before canning
If the air bubbles are not removed then the trapped air will increase the headspace, which increases the risk of a false seal.
A helpful tip is to use a plastic spatula or wooden spoon to move the ingredients around which will reduce the headspace.
2. Leave the Recommended Headspace
The recommended amount of headspace is 0.5 inches between the top layer of your food and the lid.
If the headspace is larger than 0.5 inches then consider using a smaller jar or refrigerating the food. If the food is refrigerated then the food should be consumed within 3 days.
Avoid using jars that are larger than the recommended size in the recipe.
3. Wipe the Jar Rims
Use a clean cloth to wipe grease and spilled food from the rim of the jar. Dip the cloth in white vinegar to wipe off any oil or grease.
Remember that a jar’s rim that looks clean to the naked eye may actually be dirty which will lead to a false seal.
4. Proper Processing
Follow the recommended processing time and temperature for canning.
If you miscalculate the processing times, fail to account for altitude changes, and forget to monitor the jars during processing, then the jars will likely not seal correctly.
Any jars that are not processed correctly will need to be reprocessed to create a good seal.
5. Use High Quality Jars and New Lids
Purchase high-quality jars that can withstand heat processing. The jars not crack easily.
Make sure to use the recommended jar sizes as stipulated in the recipe.
Remember that lids cannot be reused in canning so use new lids each time you are processing food.
6. Test the Seals After Cooling
Do NOT try to tighten or test the seals right after the canning. Only test the seals once the jar has cooled for 24 hours or more.
Methods for Testing if the Jar is Properly Sealed
Wait at least 24 hours before testing the jar seal. Remember that the jar needs to be cool before testing if there is a false seal.
Here are 3 methods for determining whether or not the jar has been sealed properly:
Pressing Method
Press the center of the lid with your finger.
If the center of the lid rises or springs up after pressing the lid then the jar is unsealed.
A vacuum sealed jar will not have a lid that can move or spring up. This is why a properly sealed jar makes a popping noise when first being opened.
Tapping Method
Tap the center of the lid with a spoon.
A high-pitched sound confirms that the sealing was done correctly.
If you hear a dull sound then the lid is not properly sealed. Either there is a false seal or the food was overfilled.
Eye Test
Bring your jar to eye level and examine the lid’s center.
A concave-shaped lid confirms that it is correctly sealed. Any bulge or flat lid surface indicates incorrect sealing.
Final Thoughts
A false seal is a sign that something went wrong in the canning process. If you detect this problem within 24hours of the cooling phase then you can reprocess the contents in a new, clean jar.
Once the jar cools after 24 hours, test the seal using any of the three methods before storing away the canned food.
If you discover a false seal months later then throw away the jar and its contents. It is much safer than exposing your family to food-borne illnesses such as botulism.
