The harvest of wine grapes represents the culmination of a year’s work in the vineyard, transitioning fruit from vine to cellar. This complex process involves critical decision-making regarding timing, logistics, and method. The quality of the final wine is largely determined by the condition of the grapes when they are severed from the plant. Therefore, selecting the precise day and the correct technique for harvesting is fundamental to achieving the desired style and quality.
Determining Optimal Ripeness
Deciding the exact moment to harvest is the most impactful decision in viticulture, requiring a balance between chemical analysis and sensory evaluation. Grapes are non-climacteric fruit, meaning they do not continue to ripen once picked, making the timing irreversible. Winemakers track several key chemical parameters to monitor the fruit’s progression toward ideal maturity.
Sugar accumulation, measured in degrees Brix (°Brix), is a primary metric, determining the potential alcohol level of the finished wine. A handheld refractometer measures the sugar concentration in the juice, typically falling between 22 and 26 °Brix for still table wines. Acid levels are monitored simultaneously, as they naturally decrease while sugars increase during ripening. Acidity is measured as Titratable Acidity (TA), reflecting the total concentration of acids, and pH, which measures the acid’s strength.
The ideal pH range (3.2 to 3.6) is important because it affects the wine’s color stability, microbial resistance, and overall balance. Beyond chemical measurements, a modern focus is placed on achieving “phenolic ripeness,” which relates to the maturity of compounds in the skins, seeds, and stems. Phenolic compounds, such as tannins, change from bitter and “green” to softer as the grape reaches full physiological maturity. This final stage is assessed by tasting the grapes and seeds directly in the vineyard, ensuring structural components are fully developed alongside the sugars and acids.
Manual Versus Mechanical Harvesting Techniques
Winemakers must choose between two distinct methods for removing grapes from the vine, each carrying significant quality and logistical implications. Manual harvesting involves teams of pickers using small knives or shears to delicately cut the bunches. This method allows for high selectivity, ensuring only healthy, fully ripe bunches are collected. This is beneficial for high-quality or delicate grape varieties like Pinot Noir.
The gentler handling minimizes berry crushing, preserving whole cluster integrity and delaying oxidation or premature fermentation. This traditional method is significantly more expensive and time-consuming, requiring a large labor force difficult to source during the compressed harvest season. Manual picking is also the only option in vineyards on steep slopes or where vine rows are too narrow for machinery.
Mechanical harvesting utilizes large, self-propelled machines that straddle the vine rows and use vibrating rods or bats to shake the fruit from the vine. This technique offers unparalleled speed and efficiency, allowing large vineyards to be harvested in a fraction of the time and at a lower cost than manual labor. The rapid speed is advantageous when inclement weather threatens or when a large volume of grapes must be collected quickly at a specific ripeness level.
A drawback of the mechanical method is the rougher action, which can damage the fruit and collect MOG (Material Other than Grape), such as leaves, stems, or insects. The inclusion of MOG introduces vegetal flavors and can lead to off-tastes if not meticulously sorted out at the winery. Furthermore, mechanical harvesting usually requires specific vineyard trellising systems, limiting its use in certain established vineyards.
Immediate Handling After Picking
Once the grapes are off the vine, immediate handling focuses on rapid cooling and protection from oxygen to preserve the fruit’s aromatic potential. Grapes harvested manually are often placed into small, shallow bins or lugs, typically holding 20 to 40 pounds. These smaller containers prevent the lower layers of fruit from being crushed by the weight above them, which is a significant quality consideration.
The small lugs are quickly transported to a central collection point or delivered directly to the winery’s crush pad. Grapes picked mechanically are immediately deposited into large gondolas or receiving bins, which must be moved swiftly to the processing facility. The primary concern during transport is the removal of “field heat,” the warmth the fruit absorbed while on the vine, as elevated temperatures accelerate oxidation and microbial activity.
Many wineries employ night harvesting to bring in fruit that is naturally cool, often below 50°F (10°C). For daytime picks or long transport distances, winemakers use solid carbon dioxide, known as dry ice, which sublimes directly into cold, inert CO2 gas. A layer of dry ice is placed over the grapes to cool the fruit and create a protective blanket of heavy CO2 gas, displacing oxygen and preventing unwanted browning and premature fermentation.