Why Did My Canning Jar Break?

I recently had a canning jar break during processing, and while this is a rare event, it still caught me off-guard and disappointed me a little.  I was canning Quick Dills with Garlic and Chiles and had placed my filled jars into the canner minutes earlier only to hear the tell-tale pop of a pint jar breaking in the canner.  Since I was in the middle of this canning operation, I left the jar in the canner and continued to process the remaining jars.  Once the processing time was over, however, I removed the broken jar, and this is what I found.  

Jar with bottom broken off

So, why did this happen?  Well, for anyone getting into canning and even for those with experience, this can seem like a set-back.  In actuality, it is not that big a deal although it can be messy, and it obviously means you have lost the ingredients from that particular jar to the garbage.  For the most part, this problem can be easily avoided, though.  Here are some reasons why a canning jar may break before, during, or after processing.  

• The number one thing to remember is to use jars meant for canning today.  That means no use of mayo jars or jars that once held store-bought jelly.  Those jars are meant for commercial canning which is different from canning at home.  That also means no canning in vintage jars.  I know those old blue Ball jars are pretty, but they are best kept for dry ingredients such as beans, rice, and pasta.
• We may not realize it, but each time we pack a jar or remove its contents, we are possibly scratching the insides of the jar, particularly if you are using metal utensils.  Make sure to inspect your jars thoroughly before using them to make sure there are no cracks or chips anywhere, even on the rim (which can prevent proper sealing).  To prevent cracks or chips, use plastic utensils to pack jars and remove air bubbles. I find that a plastic chopstick works great for removing bubbles in a safe manner.  
• The leading cause of jar breakage is probably a temperature difference in the jar and its surroundings.  When I was a kid, I filled a glass with ice and put it in the freezer until the tea had been made.  Once the tea was finished, I poured the hot tea over the ice in the frozen glass, and guess what?  The glass cracked.  Same thing goes for canning jars.  Packing hot food into a cooler jar, putting a cooler jar into your boiling water bath, or placing your hot jar on a cool surface after processing can all lead to breakage.  The tricky thing is that sometimes it take a little longer to pack your jars correctly before they cool down.  In that case, make sure you are packing as quickly as possible and keeping all other jars warm as you do so. 
• The last factor for jar breakage can be the age of the jar.  Although jars last years (some say as long as ten), they will eventually need to be replaced.  

I feel pretty certain that my jar cracked because it was too cool when I put it into the boiling water.  Even though it had been sterilized in boiling water and was filled with boiling vinegar before being placed into the bath, I think the jar had been too cool when the vinegar was poured in and it weakened it causing it to break in the canner.  

The main thing to remember is that this doesn't happen often and is not a disaster when it does.  If you have already begun processing, don't stop your timing just to remove the broken jar.  Yes, you may have a bit of a mess to clean up afterwards in your canner, but you don't want to stop processing and then have to start it all over again just for one jar.  That could result in a loss of quality in your other jars as well (think softer pickles if they have been partially processed and then reprocessed).  If you jar is holding something like jelly or jam, make sure you thoroughly clean the other jars before storing them.  If, on the other hand, the breakage occurs before your processing time has officially begun, by all means remove the broken jar from the water before continuing.  If for some reason, a jar breaks during pressure canning (I will be posting soon about pressure canning green beans), continue processing as usual.  Do not open the pressure canner until all the proper steps have been taken and you are sure the pressure in the canner is zero.  Usually when a jar breaks it breaks into large pieces rather than shards, so it is easy to locate all the pieces and remove them safely.  Most importantly, if this happens, keep calm and can on!