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How do food packaging companies decide how tight to make the lids on jars? Has this increased over time or am I just getting older? (continued)

Alistair Borthwick, Vancouver, Canada

Regarding the difficulty of cap removal, it may be possible to obtain an empirical answer. About 50 years ago, while working for an engineering consulting firm, I was asked to determine the average torque needed to remove the cap from a bottle of ketchup, an assignment resulting from a lawsuit involving attempted cap removal, a broken glass bottle and a severely injured hand.

I still remember the reaction in the supermarket when I bought their entire stock of ketchup, and the thanks my co-workers expressed when the experimental materials were later distributed.

Mike Vandeman, Berkeley, California, US

I feel compelled to respond to the two most recent suggestions from readers for opening a difficult jar lid. I have tried both methods – tapping the side of the lid on the counter and placing the lid under a very hot tap – and these aren’t the most effective techniques.

What works every time is to carefully use a knife blade or flat screwdriver to push the lid up while pushing down against the top thread of the glass jar.

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