It's just that the risk of scratching and thus weakening the glass is greater with metal. Obviously, over time the likelihood of that jar fracturing during the canning process is increased.

So it's not a "sin" to use a metal implement but wood or plastic is less risky.

Carol

Thanks, Carol!

Highly unlikely that you will scratch this jar - it is tempered glass. I use a plain old metal spoon and have, in 45 years of canning, never scratched the glass. Me thinks it is one of those old wives tales that never dies. There is an issue of the nickle in the composite of metal table spoons that perhaps this was born of -- or, perhaps of using a silver plate or sterling spoon that would certainly compromise any acidic ingredient to toxic levels.
Nancy

Very interesting, Nancy.
I always like the idea of ferreting out old wives tales (or urban myths as they now seem to be called).
Thanks!

Hot tempered glass can be easily shattered if struck just right with any pointed metal utensil. It's heat tolerance is relatively low. Be it an auto windshield or a canning jar. And it doesn't even require much force to do it. Thus the jar manufacturer's recommendation to use only plastic or wood utensils in them.

If you have never had it happen to you then count your blessings. :)

Dave

Okay -- I'm going with plastic.
Who would think there could be so much info about such a small point in canning!

If you wish to check further the Virginia Tech document at the link re-iterates the recommendation to avoid metal.

I might add that statistically one person's experience, even 45-years' worth, is not sufficient to disprove a point.

Carol

Here is a link that might be useful: Boiling Water Bath Canning