Determining the perfect moment to harvest grapes from the vine is an artful culmination of scientific analysis, sensory perception, and timing. The decision to begin the grape harvest involves an understanding of various indicators and factors that influence the grape’s readiness for picking and subsequent processing.
As the harvest approaches, winemakers and vineyard managers conduct extensive sampling from all vineyard areas. Using a refractometer, they assess Brix levels to measure the grape’s soluble solids (sugar concentration) . While high Brix levels typically signal ripe grapes with the potential for commercially viable alcohol content, it’s just one piece of information. The bigger picture encompasses regular assessment of acidity levels, phenolic development, flavour development, skin colour, berry size, skin tannin maturity, seed maturity, stem quality and berry detachment, all weighed against the risk of continued environmental exposure. All these human sensory elements and experiences play a vital role in determining when and how the grapes should be harvested.
Mechanical vs. Manual Harvesting
The method of harvesting, whether mechanical or manual, impacts grape quality. Mechanical harvesting certainly offers efficiency, picking about an acre per hour, but cannot be as selective as human hands. Manual picking can be done in many passes over several days ensuring only the optimal grapes get to the winery.
Timing of the Grape Harvest
Deciding whether to harvest early might be driven by the desire to preserve acidity or create specific wine types, like sparkling wines that prioritize freshness over richness. Weather conditions, especially impending wet or severe weather also influence this decision. Picking grapes during rainfall causes dilution of the juice and rain before harvest could cause grapes to swell and potentially burst, making the fruit susceptible to oxidation, rot, diseases, and pests. Night harvesting, a practice used primarily in hot wine regions, takes advantage of cooler temperatures that help maintain grape quality, specifically delicate aromatics, but also prevent oxidation. Additionally, harvesting at night can be more comfortable for workers in hot climates.
| DID YOU KNOW Grape vines can live for over 125 years, however, there yield decreases after 20 – 25 years. [1] |
Logistics of a Grape Harvest
The logistics of processing incoming grapes plays a significant role as well. Wineries often need to manage tank space, which might impact the timing of harvest for different parcels or varietals, either delaying or moving up the harvest date. However, delaying the harvest poses its own set of risks. Grapes left on the vine for too long risk becoming overripe resulting in excessively high sugar levels, declining acidity and imbalanced flavours, potentially leading to wines with excessive alcohol or overly “jammy” characteristics. Furthermore, delaying the harvest increases the risk of losing a valuable crop to disease, rot, or hungry pests.
Keep in mind that with some styles of wine a longer hang time is encouraged. Dehydration on the vine and dehydration due to noble rot allow grapes to be made into a rich, and sometimes sweet style of wine. Whole grape clusters destined for icewine also hang into the cold winter months before being picked only by hand and usually in darkness.
Final Thoughts
Ultimately, determining the best time to harvest grapes destined for wine involves a careful balance between these factors. Winemakers often rely on a combination of scientific measurements and sensory evaluation, considering Brix levels alongside the grape’s taste, texture, and appearance. Experience and intuition play crucial roles in this decision-making process, as understanding the vineyard’s unique characteristics and historical data will guide the timing of the harvest.
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The image above is a painting by Peder Severin Krøyer – Wine Harvest in the Tyrol [1901]
