Factors include variety, market demand, weather conditions (temperature, humidity), grape maturity (sugar and acid levels), vineyard location, etc.
Maturity of grapes is assessed based on their sugar content (measured in degrees Brix), acidity levels, and taste. However, in case of colour grapes, uniform colour is also considered as one of the important parameters.
In coloured varieties, the grape bunches should possess unique colour. According to AgMark standards, 16 °brix TSS is required. Good balance of TSS and acidity should be considered main criteria for grape harvesting.
Hand refractometer is used for measuring of TSS content in grape berries. Before taking the reading, calibration of refractometer is needed. For calibration of refractometer, place 2-3 drops of the water on the screen of refractometer and cover by the flap. The screen showing zero reading will ascertain the calibration of refractometer. Just wipe the screen to remove water. After that, place 2-3 drops of grape juice on the screen and cover by flap. See on the screen and record the reading.
Collect minimum 20 berries from different bunches of different vines. The grape berries should be collected from different side/ parts of bunches like upper, medium and lower; and from different directions, as well as berries from bunches from inside and outside canopy. The grape berries are then crushed using muslin cloth and the juice is prepared.
Use the hand gloves for grape harvesting. Sharp seizures are needed for cutting the grape bunches above the knot. Place one hand below the bunch and make a cut the peduncle. The bunches fulfilling minimum criteria should be harvested. Don't harvest the bunch having defected and improper coloured of berries.
To maintain the freshness of harvested grapes, harvesting should be stopped when temperature rises above 20 °C. This condition is generally available in the morning till10.00 am. Hence, early morning harvest should be given preference.
Malformed uneven sized and shaped, off coloured, dried, bruised, damaged, decayed, infection of downy mildews, powdery mildew or mealybug, thrips, etc. are considered as defected barriers.
Grapes should be handled gently to avoid damaging the clusters. Using sharp, clean pruning shears to cut clusters from the vine helps minimize bruising and ensures grapes remain intact. After harvest, place the bunches in cushioned crates gently, avoid direct touching of grapes with soil, use light coloured clean crates, always place the crates inside shade, etc.
Grapes should be transported in crates that allow airflow for freshness in berries. It's essential to avoid overfilling containers to prevent grapes from being crushed under their own weight. Not more than 2 layers of grape bunches should be allowed.
White powdery coating on grape berries is naturally occurring coverage known as bloom. Removal of the natural protective bloom on the grapes is helpful in maintaining the freshness of grapes and increasing shelf life. Bloom has no adverse effect on human health.