Just not quite ripe -- maybe the brix will go super high in the next few weeks as they ripen more? Or, maybe the extreme heat in your region is somehow supressing the pigment formation, or keeping the chlorophyll alive, kind of the way leaves don't get good fall color in very warm autumns?

Just guesses.

Agree, they just aren't ripe yet. Mine when ripe are mid to upper 20s or higher brix.

Mine are just turning and they are delicious. I actually prefer them with a little sour or else they turn into candy. The kids have been eating them every day. One of my favorites.

Why are they so late compared to everything else though? Lack of water? Which is what I figure has them so sweet.

16-18 brix isn't high for a grape. I'd say they are a month away from being ripe based on their color. Most grapes and cherries are picked way before optimum time because of birds or other outside factors. You probably haven't eaten a ripe one yet and won't without bird netting.

Birds leave mine alone, but the vine is right next to the house... Not sure why they aren't earlier...mine get some shade during the day, so i've always thought that slowed them some. Lack of water? could be. All this heat can't help, but then again I think they grow grapes in the desert of California.

I doubt mine make it until they are fully ripe. The kids eat them too fast.

Fruitnut, when I picked them 2 years ago they were ripe.
I can agree that it's probably a month away but that doesn't explain why my apples were/are a month early (starting to get red drops from McIntosh, which is usually more towards the end of August), plums were early, raspberries and strawberries were a month early, early dropped butternuts were early, cherries were early.
Grapes will be comparatively almost 2 months late, going by everything else I was expecting them in mid-July.

I looked up the brix of Reliance specifically, the university I found said 18-19.

Frank,

Mine won't last because of the birds if they don't hurry up and ripen. The birds have been hitting them for a good month.
I'm going to have to figure something out for birds. And I'm pretty sure it is birds now, I bagged more figuring if they rot in the heat at least it gives me a chance. One of the birds is smart enough to figure out how to open the bags. It's not the squirrel bite marks I get with my apples.

They get no shade.