Recipe(tried): Pickled Asparagus

Hmmm, the brine is half water/ half 5 % acidity vinegar, dill, one clove of garlic to a jar, dried pepper flakes, and salt. Should not be a problem with it. I have the book, too, so checked. I wouldn't cut down on the salt. The only other thing I can think of is if you used an aluminum pan, that could have caused it. I use the one from our extension office.
Here is my tried and true recipe:

Pickled Asparagus

8 pints asparagus spears
6 cups water
6 cups white vinegar 5% acidity
6 Tbsp. canning or pickling salt
2 tsp. pickling spices, cloves removed
garlic, 1 clove per jar

Wash asparagus, cut into jar length spears.

Combine water, vinegar, salt, and pickling spices, tied in a cloth bag. Heat to boiling, Remove spice bag.

Pack asparagus into jars, add garlic clove. Cover with boiling brine. Leave 1/2 inch headspace.

Process 10 minutes in water bath canner.