Why should I buy special preserving jars: can’t I just reuse jars from the supermarket?

We sometimes get asked this question and concerningly, there are numerous sites on social media that actively promote the practice.  This relates to reusing jars such as those you might buy with mayonnaise, tomato pasta sauce or premade sauces.

So to step back from the question, a quick refresher on what a good preserving jar should have:

Tempered glass: this will allow the glass to withstand higher temperatures. 

A secure seal: preserving jars differ in how they achieve this.  Some may have a separate rubber seal or gasket (like Le Parfait or Weck jars) and some have the seal built into the canning lid (like Ball or Familia Wiss jars).

A way to tell if the seal has failed: again, the way different preserving  jars do this differs.  For instance, Ball jars have a 2 piece lid consisting of the lid that incorporates the seal and a pop top, and a screw band that holds the lid in place during processing.  When the jar has cooled, the pop top will depress given an immediate indication of a seal.  For storage, the band is removed, so if the seal fails over time the lid will simply lift off.  Jars that use separate rubber gaskets like Le Parfait and Weck hold the seal and lid in place during processing using either a wire bail or clips.  The gaskets have a little tongue on them which sits in a downward facing position when the jar is correctly sealed allowing the metal clip or bail to be removed, which again allows you to periodically check if the seal has failed during storage.

In Australia, virtually all shop sold jars have a twist top style lid: these types of lids are also called lug lids because they have several lugs on the inside of the lid which locks onto the thread of the jar by a simple half twist.  By contrast, metal lids on preserving jars are a screw top or continuous thread lid.  As the name suggests, these lids screw down onto the jar thread, given a more secure closure than a twist top  lid.  Whilst there are some deep twist lids around which are about the same height as a twist top lid, as a general rule, twist top lids are shorter and less substantial  than screw top lids.  Some may incorporate a pop top which allows you to see if the contents are sealed but many do not.  It is important to note here that the thread on a jar that takes a twist top lid differs to a jar that takes a screw top lid and the lids are not interchangeable between the 2 styles.  The point is that twist top jars do not offer a secure seal such as specialty preserving jars do. 

The way that food contents of shop bought jars are heat processed for sale involves industrial machinery and processes that are beyond those achievable in a home kitchen.  So whilst it may be correct to say that the product you bought from the supermarket in a jar with a twist top lid was perfectly safe to eat, it does not therefore follow that it is safe to reprocess that same jar with your own contents, even if you use a brand new lid.  Essentially, it is our belief that home processing with twist top lids does not provide the same security of seal that you obtain from the same lids processed via industrial manufacturing.

Furthermore, as noted above, specialty preserving jars are made of tempered glass.  There is little likelihood that a shop bought jar will be of the same high- quality glass which leads to the risk that the jar could break during processing, losing all that food you have carefully prepared to save.  Worst still, untampered supermarket bought jars can sometimes explode when exposed to heat, leading to a potentially dangerous situation if you are in the wrong place when it happens, or even just cleaning up the mess.

On the final test of the features of preserving jars, about being able to tell if the seal has failed, some twist top lids have a pop top lid which will indicate that the jar contents have sealed.  Also even lids that do not have a pop top will bow inwards slightly in the presence of a vacuum in the jar, indicating that the contents have sealed.   Whilst they may meet the criteria on this point, they fail on the other essential features required to qualify as a good preserving jar.

A special word about reusing supermarket jars for pressure canning.  Pressure canning allows you to process food above boiling temperature and is the only method recommended for preserving non-acidic food (ie most vegetables, meat, fish, chicken, soups, etc).  Failure to process non-acidic food correctly can lead to botulism, a potentially fatal form of bacteria which is both tasteless and odourless.  For this reason, and rightly so, organisations such as the USFDA urge great caution when pressure canning food and recommend that tested recipes are used.  There are currently no tested recipes using twist top style jars. It is our opinion that anyone who attempts to use twist top jars for pressure canning food is at best courting danger.

Proponents of the practice level the criticism that it is only due to our commercial interest that we denigrate the use of twist top jars for preserving.  However it should be noted that we do stock and resell twist top jars and lids.  We feel it would be negligent for us to watch the practice proliferate and go uncriticized, potentially exposing innocent beginners to injury or harm to their health.   Some sites also justify the use of these types of jars in Australia and New Zealand due to the high cost of preserving jars compared to the prices in North America.  Whilst this may still be the case, in relative terms preserving jars are now much more affordable now than they may once have been.

In the end, home preserving is about growing or catching your own food and preparing it to store for a later time.  When you go to that sort of effort and expense, it would seem to be a false economy to use jars that statistically have a higher rate of breakage and seal failure than jars that are manufactured and tested for the purpose.  Some jars such as Weck jars or Le Parfait jars have glass lids and the only part that needs to be replaced after heat treatment is the rubber seal.  This may mean an initial higher outlay than would be incurred recycling shop bought jars, but we contend that the dividends over the long term heavily weigh in favour of the specialty preserving jars.

So what to do with all those shop bought jars?  There are  still many ways you can