Hi Emily, 

Because grape leaves are naturally a low acid food, the Extension Service strongly advises only using tested recipes for canning. Improper canning of low acid foods is a leading cause of botulism poisoning. 

Unfortunately, I cannot find any lab-tested recipes for home canning grape leaves, either as an acidified food (which would be safe for water bath canning) or unacidified (which would require pressure canning). I can see that the Spruce recipe does call for lemon juice to be added, but without lab validation there is no way to know if the added lemon juice is enough to prevent the growth of harmful bacteria. 

Given the lack of adequate testing, I would advise you to dispose of those jars without tasting. 

Regarding the crystals you're seeing in your jars, they are likely tartaric acid crystals, which commonly form in home canned grape products. The mineral crystals are harmless, but the larger concern is the potential for the growth of pathogenic bacteria.

Thanks for using Ask Extension, 

Jared