How to Seal Glass Jars

Instructions

Turning them upside down

Probably the simplest method to get vacuum sealed glass jars is to simply turn the jars upside down. It’s an old-fashioned method that was probably tried and tested by your mother, your grandmother and your grandmother’s mother!

Otherwise known as ‘inversion canning’, this method only works if your preserves are hot in the jar. 

1. Once you’ve spooned your hot chutney, jam or other preserve into the jar, simply place the lid on securely (wearing gloves!) and turn the jar upside down on a dish cloth. Then leave it for 5–15 minutes.
2. Next, flip the jar the right way up and allow the jar to cool for at least 30 minutes. After a few minutes, you should hear a ‘pop’ sound. This is the sound of the heat creating a vacuum. 
3. Once your vacuum sealed jars have cooled properly, they are ready to be stored in a cool dry place. Depending on the food storing, you’ll typically be able to store it for a year.  

While inversion canning is quick and easy, it’s not the safest method. The vacuum seal is far weaker and less durable than other vacuum sealing methods.

Sealing with a water bath

Water bath canning or a ‘boiling water bath’ is a quick and effective way to vacuum seal jars. 

1. First, place a round metal cooling rack on the bottom of a tall cooking pot. This is to keep the jars from touching the base of the pot, allowing evaporating water to escape from the pot. 
2. Next, fill the pot with water – enough to cover at least an inch above your glass jars. Turn up the heat to a heavy simmer.
3. Carefully lower your filled canning jars into the boiling water using a jar lifter. Make sure to keep each mason jar upright, to avoid your preserve making contact with the lid (it’s important to keep that gap at the top!)
4. Turn the heat up to a rolling boil. Boil for 10–15 minutes.
5. Take the pot off the heat and let it cool for 10 minutes.
6. Remove the jars using the jar lifter. Allow them to cool for 12–24 hours. When they’ve cooled completely, press down on the lid of each of the sealed jars. If the lid doesn’t pop, they’re sealed properly. 
7. Wipe away any residue from the outside of the jars and store them in a cool dry place for up to a year.

Steam canning using an Instant Pot

This method involves making sure your jars are properly sealed by using a pressure cooker or an Instant Pot.

1. Add one cup of water to your instant pot.
2. Place your warm jars full of hot food into the rack inside your Instant Pot. Make sure the pressure valve is set to ‘empty.’
3. Press the ‘steam’ button on your Instant Pot.
4. When the Instant Pot’s float valve pops up, you’re ready to start the processing timer.
5. Set the timer to 10 minutes. If you’re 3,000 feet above sea level or more, increase the processing time by 10 minutes.
6. Press ‘cancel’, ‘keep warm’ or simply unplug your Instant Pot.  
7. When the float valve goes down, carefully open your Instant Pot (careful with the steam) and use the jar lifter to remove the jars.
8. Place jars on a cooling rack and leave them to cool for 12 hours.

Vacuum sealing

Another quick and easy way to seal glass jars is by vacuum sealing. The vacuum sealing process is very straightforward and doesn’t involve boiling water or high temperatures – just a vacuum sealer and a hose attachment. You can only vacuum seal glass jars with metal canning lids – plastic lids are not suitable.

1. Secure the lid to your mason jar.
2. Place one end of sealer hose into your vacuum sealer machine and the other into the jar sealer attachment.
3. Place the jar sealer attachment on top of the glass jar lid. Push down to secure it into place.
4. Turn on your vacuum sealer. Follow the machine’s operating instructions to properly seal your jar. The machine will indicate when the sealed glass jars are ready. You should also hear a ‘pop’ to indicate that the canning jars are properly sealed. 

Paraffin wax

Sealing canning jars with paraffin wax is an old school way to seal canning jars is to use paraffin wax. We don’t recommend it, but set it out here for your reference.

1. Place a wax sealing dish on a flat surface (a table or kitchen countertop will work fine). Light a candle and place it in the space below the sealing dish. If you don’t have a sealing dish, heat the wax slowly in a small saucepan.
2. Place your paraffin wax into the dish or saucepan so it can heat up. Start with a small amount and add more as needed. It’s important to melt the wax slowly – if it overheats, it will shrink when it cools. This means it won’t create an effective seal.
3. It should take around 20–30 minutes for the wax to completely melt. Once melted, pour a thin layer over the top of your cooled preserve. 
4. Leave for a few minutes, then pour another thin layer. 
5. Now place the lids on. When the wax cools, it will form a vacuum seal. Place your canning jars in a cool dry place.