Concord grapes are the essence of autumn. They are American in origin, cold hardy and late ripening. The best way to tell if the grapes are ready for harvest is by tasting them and by checking the seed color. As the fruit ripens, the seeds will change from green to brown.
Keep in mind that juice from Concords grown in the Willamette Valley will not be as sweet as juice from the same grapes grown in Hermiston. If we get an early frost, and dry days, the grapes will become sweeter. However, our more typical fall of gradual cooling then rain and no frost doesn't make for sweet Concord grapes. Keep the grapes on the vine as long as possible but at the same time, keep an eye on the weather. If we're heading into a prolonged rainy period consider harvesting if the grapes seem to be close to being ready. You can always add a bit of sugar to the juice if it is too tart for your taste. Enjoy your taste of autumn!