I am no expert here but my ribs pull away from the bone almost an inch before they are done. I grab the rack in the middle with some tongs and if they almost bend into an inverted horseshoe they are done. Otherwise I take a toothpick and slide it into the meat between the bones in the thickest part. If a tooth pick slides in easy I say they are done.
Never give up as others said. Once in a while I get some tough ribs too.
Click on this link......located at the top of Q-Talk. http://www.bbq-brethren.com/forum/showthread.php?t=7818
. Go to post #5 and see if this helps.
"You have never really lived until you have done something for someone who can never repay you."
"I wish my mind could forget what my eyes have seen.
"Heavily medicated for your protection.
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