It’s obvious to even casual wine country visitors when harvest has begun. Teams of pickers with bright yellow trays swarm the vineyards, their dusty vehicles lining road shoulders. Hulking, bin-laden trucks sway down thoroughfares at worrisome speed.
But considerations about how and when to harvest begin much earlier, proceeding quietly behind the scenes. Plans are made, sometimes changing day-to-day, based on myriad factors. The decision tree is anything but simple.
Among the questions that must be answered: Are the grapes ready? Should we pick everything at once or make multiple passes? Will we harvest by hand or machine? These are crucial decisions that can significantly impact the resulting wines—making or breaking a vintage.
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Myth #1: Harvest Date is Decided by Measuring Sugar Content and Tasting Grapes
Yes, every grower and winemaker measures sugar and bites into bunches of grapes to evaluate the crop’s readiness. But that’s not how harvest dates are set.
The state of grape maturation is paramount, but ripeness isn’t boolean. It’s a process with many elements constantly in flux. “Ready” for one producer, given the style they go for, may also be too late, or too early, for another.
Sugars increase as the season progresses, but go both up and down over the course of each day. Malic acid decreases, but at an inconsistent rate. Grape skins get darker and their tannins softer. Fruit flavors not only transition from tart to ripe, but change in character with increasing—and then decreasing—complexity. Water content decreases, increasing concentration of flavor, sugar, acid, tannin, and color. Seeds change from green and astringent to brown and crunchy. Stems become more lignified and less green in flavor.
Producers want the best possible intersection of all those aspects relative to the intended wine character. But harvest isn’t instantaneous. It has to be scheduled. So winemakers project when the ideal date and time will be, based on the trajectories of all these factors and the conditions that can change those curves. Then, they book their harvest labor.
But even when the schedule is set, there are plenty of variables that may cause last-minute changes. These include practical concerns like available room on the crush pad and in fermentation tanks, and weather concerns like frost and hail. In other places, harvest is also a race between man and beast—birds, deer, and bears love good grapes.
Myth #2: Everything Gets Picked on “Harvest Day”
For many high-volume crops, harvest is all or nothing. There is a time when virtually all the lettuce, celery, and wheat in a field is sufficiently mature, but not overripe. Pickers, or machines, sweep through, taking the whole crop. Many people assume grapes are the same way, but that’s not the case.
Factors affecting ripening can vary from one part of a vineyard to another, even vine by vine, from the bottom of the canopy to the top, or one side to the other. Here are some of the variables that affect ripening and may cause winemakers to harvest on multiple dates:
- Type, depth, mineral content, organic content, and health of the soil
- Slope (affecting drainage and aspect to the sun)
- Being in a bowl or gully, on a hilltop, and in proximity to a hill, stream, lake or seaside, affects temperature, wind, fog, humidity and, sometimes, sunlight
- Being near the beginning or end of an irrigation line
- Individual vine age
- Temperature, wind, and humidity vary with height from the ground
- Vine orientation
- Vine training and trellising
- Amount of and positioning of leaves in the canopy
- Exposure of individual grape bunches to sun and airflow
- Bunches per vine
- Presence of competing vegetation, such as trees and cover crops
- Varietal clone
- Presence of dust (from nearby roads) on grapes and leaves
- Vine disease
Growers and winemakers may choose to harvest in one pass if vines of a particular variety show uniform ripening between plots, or if the volume of wine being made is so high that somewhat uneven ripening will add complexity. The decision to multiple passes for best possible ripeness is also determined by practical issues, such as availability of labor and harvest equipment; labor costs; wine selling price and margins; number, size, and availability of fermentation vessels; and anticipated weather.
Harvesting over multiple passes is a common technique used by wineries making small lots of wine. The goal is to ensure consistent ripeness, or to create complexity with a gradient of maturities. There may also be practical matters that dictate whether multiple passes are crucial or impossible.
Myth #3: Manual Harvesting is Better than Mechanized
In most circumstances, hand harvesting has the potential to produce better results than mechanical harvesters. Human workers can pick bunches carefully and lay them in trays gently. People can be selective too, leaving bunches with sunburn or rot on the vines. And, while stray leaves may find their way into the trays, there won’t be much material other than grapes (MOG), such as pebbles and lizards.
The degree to which this care is actually realized depends on a number of things:
- Picker expertise—Are they long-serving professionals, family members, or newbies looking for an experience?
- Picker motivation—Pay level (and by hour, weight, or project), financial interest in the winery, fatigue
- Picking conditions—Temperature, humidity, time of day, lighting, terrain, vine height, vine training
- The need for speed versus quality
Historically, mechanical harvesters have had limitations and drawbacks. There are vineyard configurations where they don’t work, such as steep or undulating vineyards, short or crooked rows, narrow spacing, and difficult soils. The machines—which operate by straddling a row and shaking it vigorously so bunches fly off the vine into a hopper—also require certain types of vine training (specific trellises, and not head trained). And the shaking can severely damage old vines.
The rougher nature of the harvest can also lead to lower-quality yield. Grapes may be broken or crushed. Selective picking isn’t possible. MOG flies into the hopper as readily as grapes.
But mechanical harvesters have steadily improved. They treat vines and grapes much more gently than they used to. Recently, harvesters have been introduced that use optical sensors and forced air to sort grapes immediately, discarding MOG and grapes or bunches that are rotten, raisined, pale, or undersized.
High-quality sorting harvesters can potentially improve wine quality over hand-picked grapes by eliminating sorting bottlenecks on the crush pad. Harvested grapes can sit for hours in the heat of the day, stacked high in one-ton or larger plastic bins while they wait to go through the crusher-destemmer and sorting tables. If destemming and most sorting is done on the fly in the field, grapes arriving at the winery can go straight to final sorting or even direct to the fermentation tank.
Still, mechanized harvesting doesn’t come close to the potential for gentle and selective, bunch-by-bunch picking that trained workers offer. But in some big growing areas, such as Lodi, California, there is not enough labor available to harvest all the fruit manually. Even in Napa Valley, with its extreme quality focus, labor shortages are leading to increasing mechanization. High-end, well-moneyed wineries will likely drive increasingly swift improvements in these machines.
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Fred Swan is an Oakland-based writer and educator on wine and spirits. Among his credentials are Certified Sommelier, WSET Diploma, French Wine Scholar, Sud-France Wine Master, Italian Wine Professional, and Certified Specialist of Wine.