Canning Concord Grapes

This year, for the first time in my memory, I canned Concord grapes for juice.  I have usually not had access to grapes at an economical price, but this year someone in the community had them shipped in from New York, and sold them for $11.00 per half bushel.  They were delicious.  If only we could have eaten them fresh a little faster there would have been none left to can.  Partly because my canning jars were nearly all full, I decided to attempt to can a grape juice concentrate, rather than go by the recipe I found online, which called for 1 1/3 cups grapes to each jar and 1/3 cup sugar.  The jars were to be filled with boiling water.  By multiplying that by three, I came up with a recipe that called for 4 cups grapes and 1 cup sugar per jar.  I reasoned that when I open the jar I can simply add two jars of water and have just the right concentration of fruit  juice and sugar in the final beverage.  the sugar ended up taking up so much space that I probably didn't quite get 4 cups of grapes into the jar.

Something I did not anticipate happened, however, and I need help figuring out why.  The contents seemed to expand during processing, and, besides bubbling over enough to color the canner water purple, they continued to bubble after I took them out of the canner.  The tea towel and counter on which I placed the jars are both stained purple.  What's up with this?  Thankfully the jars all sealed.

The sugar did not all dissolve either.  Each jar has a layer of sugar on the bottom.

I need help from grape canning veterans?  Do you use a syrup?  Do you cook the grapes before putting them in the jars?  Is the sugar layer on the bottom normal?  Is my recipe at fault?  Is trying for a concentrate not a good idea?

I thought I was being smarter than my mom (who thought she was also being smarter than her mom) by making a concentrate.  My mother said that her mother used to put one cup of grapes and one cup of sugar in each quart jar before filling it with boiling water.  My mom halved the sugar and still put in one cup of grapes.  My recipe calls for even less sugar than my mom's, and calls also for more grapes per jar.  Does anyone from grape growing country wish to share their methods and recipe?

I hope that some time in the future we'll have grapes from our own vines.  In the meantime, I'll be a customer if the Troyers on Red Rock Road bring in New York grapes again next year--and if I can figure out how to do the canning right.