Last year (January) I made my first canning attempt - about 1/3 dozen
small jars of grapefruit marmalade. I thought I was being very
careful.
When they cooled, each gave a satisfactory 'click'.
Yesterday I picked up the first jar and pushed upward on the lid with
my thumbs. With very little pressure, the lid came off. I pitched the
contents.
The same with the second, third and fourth jar.
Any ideas what may have gone wrong? - Mike