This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
From: Scott Murman
If you're getting mushy peppers its likely that you're leaving them in the
water bath too long. Peppers will get soggy quickly, try and stay in the
10-15 minute range. You can try adding alum, but I've never been able to
find it, so I can't comment on how well it works.
[ peppers will go mushy in time no matter what you do. The only remedy is
eat, eat, eat and eat before momma-time says, "clear the table". Other
solutions are 'make less or give more away' - ED