Glass Jars for Pressure Canning
The jar market is very confusing and we will try here to guide you through to the right jar for you.
CLIP TOP OR SCREW TOP?
If you intend to do a lot of pressure canning we would suggest that you seriously consider the two-part screw top seal and lid version of canning jar. It is so much easier to handle when trying to fill the jars especially if you are hot-filling. The seals go into boiling water to sterilise and can be taken out individually when you are ready to seal. The screw band can then be applied finger tight - before the jar is added to the canner.
If you choose the clip top jars you have to allow for the considerable weight of the lid as it is opened and hinged down the back of the jar. When the jar is still empty it is unstable in this position and needs to be supported while you ladle in the contents. If you are hot filling, the jar will have been pre-heated as well so your hands will need to be protected while you support the lid.
We tend to use the screw band type for our own use and the clip top version if we are making products for sale or for hampers because they are arguably more attractive and are more familiar to the general public.
Whichever you choose, the seals are crucial. They must be in good condition so, in the case of the rubber seals on the clip top jars, inspect after every use to see if they need replacing. They can become dry and perished after a while. Make sure that you apply the seal with the little tongue roughly halfway between the hinge at the back and the clip at the front. This is how the jar is opened - pull on the tab to release the vacuum seal. If you trap it under the spring clip at the front you will have a problem getting hold of it.
The metal seals in the two-part system must be a new seal every time, no ifs or buts. As with ordinary jam jars, there is no point gathering your ingredients, prepping and making your preserve only to compromise it by using old lids which may result in spoilage. The screw bands can be used over and over again as they are only applied for the pressure canning processing and for 24 hours afterwards. They are then removed to check that the seal has been successful and then they can be washed and dried and then stored away until next time. The jars are never stored with the screw bands in place. Sometimes - rarely - seals fail during storage due to some error made in the processing and if the screw bands are still in place the jar could explode. If they are removed, the seal can ‘pop’ without you having a big mess to clean up. For the same reason do not store your jars upside down.
You will also need to decide which style to choose between the wide mouth design or the jars with a shoulder and a narrower neck. They are mostly available in both versions and with clip tops or screw bands. We prefer the wide mouth version as it is easy-in, easy-out and nothing gets trapped under the shoulder.
WHICH MAKE OF JAR?
Now we know which style of jar fits our needs we need to decide which make to buy. There are several specialist jars on the market from different manufacturers and a lot of lookey-likey products from big retailers. These cheaper, unbranded jars are almost always unsuitable to withstand the higher pressure generated by the canner and the seals are not the of the same specification, although they are perfect for storing dry goods in your cupboards.
We would advise buying the best jars that you can afford and they will last you a long time providing that you look after them. Keep a stock of suitable seals all of the time and then you will always be ready to take advantage of a crop however it presents itself.
HOW TO CHOOSE?
Most people tend to buy on price, but as we have said above, this doesn’t always stand you in good stead. Even if you choose one of the ‘big names’ you may still find that you are disappointed. To help you through this important process we have carried out some tests. Bear in mind what you are asking of the jar - you are expecting it to be repeatedly heated and cooled, put under pressure and maintaining the vacuum within the jar for the lifetime of its storage. You are going to need a jar that is fairly strong.
We have taken the leading makes and compared them by weight - it stands to reason that the heavier the jar the stronger the jar will be as it has a larger glass content.
We have also compared the seals. The Le Parfait metal seals are very heavy gauge and cannot be easily bent by hand unlike their competitors which are very thin metal. The thinner the metal the more easily they will buckle under pressure. We have a comparison chart which displays the weights of the various makes.