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The color of the vine also indicates when to harvest Concord grapes. Throughout the growing season, the vine and stems are a light to medium green. When the vine and stems begin to turn to a light then medium brown, it means the grapes are ripening and ready to harvest.
Dark green grapes are usually not ripe. A newly planted grape vine (Vitis vinifera) can take five or six years to produce an adequate grape crop, but those early crops are a fine reward for your efforts. Don't pick them until they're at their peak though. Grapes won't ripen off the vine.