I have 'King of the North' juice grapes in my backyard that I use for jelly making. I always seem to pick them a little too early. How do I know they are ready to pick?
As grapes ripen, they first turn color, and then they become more sweet and less tart (acidic) over several weeks. Most varieties are harvested in September in Minnesota, with a couple ripening in late August or early October. There are a few ways to tell if your grapes are ready to harvest.
If you are using the grapes for fresh-eating, jelly or juice, it is fine to harvest them based on taste. In other words, taste-test a berry every few days and harvest the clusters once they are sweet enough for your liking and have lost their tartness.
They should not have a “grassy” or “bell pepper” flavor when they are ripe. The good news is, if you harvest them too early and then realize afterward that they’re not sweet enough, you can add more sugar to the juice or jelly you are making.
You can also time your harvest based on the sugar content and pH of the grapes. If making wine from the berries, it is important to know both their sugar content and pH before harvesting. Refractometers are a simple tool that measures brix, which is a measure of sugar content.
Most grape varieties should be harvested when the brix is between 20 to 25 depending on the variety. Grapes should be harvested when their pH is between 3.2-3.5. Therefore, those making wine from their grapes should have both a refractometer and a pH meter on hand to help decide when to harvest. Small, low-cost, handheld versions of both of these tools can be purchased online or at home-brewing supply stores.
For more information about harvesting grapes, download the free Growing Grapes in Minnesota guide from the Minnesota Grape Growers Association.