The Concord grape, formally known as Vitis labrusca, is a distinctly American variety cherished for its robust, “foxy” flavor used primarily in juices, jellies, and non-traditional wines. Determining the precise moment of harvest is paramount because, unlike some other fruits, grapes do not accumulate additional sugar or ripen further once they are separated from the vine. Successful harvesting relies entirely on achieving the perfect balance between the fruit’s natural sugar content and its inherent acidity while the cluster is still attached.
General Harvest Window and Visual Cues
The typical harvest window for Concord grapes occurs in the late summer to early fall, often referred to as the late mid-season. As the fruit matures, the color progresses from green to a deep, blue-black or purple hue across the entire cluster. Full coloration is necessary, but it is not a sufficient indicator of peak flavor ripeness, as grapes can appear fully colored for weeks before internal maturation. Ripe Concord grapes also develop a dusty, white film on the skin, known as “bloom.” This natural protective layer indicates the grapes are in good condition.
Sensory and Internal Indicators of Full Ripeness
The most reliable method for determining peak flavor is a direct taste test, monitoring for the transformation from tartness to a rich, full-bodied sweetness. As the grapes mature on the vine, the acid levels naturally diminish while the sugars concentrate, leading to the pronounced “grape” flavor that Concords are known for. Tasting grapes from various parts of the cluster and from different vines over several days helps confirm the flavor has fully developed.
For a more scientific assessment, the sugar content of the juice can be measured using a refractometer, which gives a reading in degrees Brix. Concord grapes intended for juice or jelly are typically harvested when they reach approximately 15 to 16 Brix, a level lower than that required for most wine grapes. Harvesting at this specific range prevents the intense, musky “foxy” notes from becoming overwhelming after processing.
The internal structure of the grape also provides clear signals that the fruit is ready to be picked. When a grape is cut open, a fully ripe Concord will have seeds that have turned a dark brown color. Green or white seeds signify that the grape is still immature and that the sugar accumulation process is not yet complete. Additionally, ripe grapes should feel plump and juicy, giving slightly when gently squeezed, rather than being overly firm.
Another practical indicator of ripeness is the ease of detachment from the stem. When a cluster is lightly lifted and shaken, ripe grapes should separate easily, a process known as “slip skin,” which is characteristic of Vitis labrusca varieties. Grapes that resist separation or require a firm tug are not yet at their peak maturity. This combination of flavor, seed color, and physical characteristics confirms the optimal time for harvest.
Essential Post-Harvest Steps
Once the grapes are determined to be fully ripe, they should be harvested by cutting the entire cluster stem with shears or clippers, rather than pulling the grapes by hand. This technique preserves the integrity of the cluster and reduces the risk of crushing individual berries. Concord grapes have softer, more fragile skins than many table grape varieties, making gentle handling necessary to prevent splitting and premature decay.
Grapes should not be washed immediately after picking, as the introduction of moisture significantly accelerates the spoilage process. The bloom coating also acts as a natural barrier that is best kept intact until the grapes are ready for consumption or processing. If immediate processing is not possible, the harvested clusters should be moved to cold storage quickly.
For short-term preservation, the grapes store best when refrigerated at 30 to 32 degrees Fahrenheit with high humidity. They are highly susceptible to absorbing odors, so they should be stored away from strongly scented items like onions or garlic. For making juice or jelly, the best quality product is achieved by processing the grapes immediately following the harvest.