Harvesting Wine Grapes
Mechanical harvesters are large tractors that straddle grapevine trellises and remove berries or fruit clusters from the vine by gently vibrating the vines so that the grapes are separated from their stems. Once the berries or clusters have been shaken free, they are collected by individually sprung “fishplates” that open and close around the vine trunk or trellis supports. The plates are angled to divert fruit to the conveyors. The grapes are then moved along a conveyor (in the case where the harvester is not equipped with an on-board bin) where powerful hydraulic fans suck off and chew up leaves and debris. Magnets are typically used by the harvester to remove nails, staples, or other metallic parts shaken loose from the trellis. The conveyor deposits the fruit into a gondola. From there, when full it is either transferred into 5 to 8 ton (4.5 to 7.2 mt) tubs which are loaded onto a flatbed truck or the fruit is directly emptied into a truck from the gondola for immediate transport to the winery. For most vineyards, there will be a single harvest. Listed below are the advantages and disadvantages of mechanical harvesting.
Vineyard Physical Configuration
Before purchasing a mechanical harvester, the wine grape grower must take into consideration a number of factors: (1) ground slope, (2) turning radius, (3) row-spacing, and (4) trellising.
Machine harvesting may be done on hillside too. Most manufacturers advise that their machines will be able to handle a vertical climb of 35 degrees while a side slope should not exceed 20 degrees.
The headlands must allow for ample turnaround space for harvesters.
Harvesters are not adjustable from side to side. All manufacturers will, however, offer units that accommodate different row spacing, but that is usually between six to eight feet. Eight feet (2.4 m) is generally considered the optimum and 12 feet (3.7 m) the maximum.
A major limitation of mechanical harvesting can be a vineyard’s trellis design. Vertical shoot position (VSP) is considered the best trellising system to use because it allows unobstructed access to the fruit zones. T-bar designs must be examined carefully because harvesters are limited by their front-end (tunnel) opening.
Just about any variety can be harvested by machine, but some are easier than others and still others may simply be impractical from an operational and wine quality standpoint.
Mechanical Harvester Configurations
There are three basic configurations of mechanical harvesters: (1) a dedicated, self-propelled harvester, (2) a tow-behind harvester using a tractor or (3) a multi-function, self-propelled unit that can be used for additional options, such as spraying or hedging.
Dedicated harvesters are configured in two ways: they either collect fruit into on-board bins and off load to trucks or gondolas when full (See Figures 33.2 & 33.3) or they transfer the fruit via conveyor to following trucks or gondolas (See Figure 33.4). Collection of fruit into onboard bins automatically limits production speed. Generally, the use of bins on harvesters is relegated to the smaller vineyard.
Tow-behind harvesters (See Figure 33.5) can accomplish the same production as the self-propelled units but are considerably less complicated (no engine or related drive hydraulics) and cost considerably less than dedicated harvesters.
Multi-Function, Self-Propelled Units
Multi-purpose, self-propelled grape harvester machines, as their title suggests, are capable of performing a range of vineyard tasks, if the available attachments are purchased. For all intent and purposes, these machines are the equivalent of a tractor, they can be used, not only for grape harvesting, but also with the necessary attachments, for spraying, fertilizer spreading, wire lifting, vine pruning and trimming, among other things.
Mechanical Harvester Options
Points that must also be taken into consideration in the buying decision include the range of optional and other features of the different models available that may include such things as automatic transmissions, adjustable picking heads, tire equipment, discharge options, auto leveling (critical when working on hillsides and/or uneven terrain), magnets for removing unwanted metal items and method for removing leaf and other unwanted material before the harvested grapes enter the holding bins.
Types of Picking Heads
Harvesters are usually classified according to the mechanism by which they apply force. There are two basic harvester designs. Those that apply force directly to the bearing shoot are called trunk shakers and those that supply the force directly to the canopy, known either as pivotal striker and bow-rod picking heads.
The trunk shaker harvester has two parallel, oscillating rails that vibrate the cordon or upper trunk. The grape trunk shaker head moves the vine with berries to the right perpendicular to the vine row, and while the berries are moving right, the head reverses direction, moving the trellis to the left. This is accomplished be a pair of horizontal picking rails moving along the trellis.
Pivotal Striker and Bow-Rod Picking Heads
Pivotal striker and bow rod picking heads are canopy or foliage shakers. Canopy shakers were designed for cane pruned vines or when cordons are young or with other systems where the fruit is not near the permanent vine structure. Canopy harvesters are not as efficient at dislodging fruit close to the vine head. Increasing the striking velocity to dislodge the fruit accentuates vine damage and increases fruit contamination with leaves, leaf fragments, and other vine parts.
Bow-Rod Picking Heads. Construction of bow-rods may vary from manufacturer to manufacturer and as the name suggests, the head consists of long loops or bows usually about 5 feet (1.5 m) long attached to a harvesting channel (See Figure 33.6). The operators can configure the harvester by varying the number of bow rods, length, weight, and the angle of the bow-rods as well as adjusting their height and the width of their gap around the vine.
Pivotal Striker Picking Heads. Most of the commercial harvesters use pivotal strikers that possess a double bank of upright flexible rods arranged parallel to, and on each side of the vine to remove fruit. Working in unison, they move rapidly and simultaneously, left-right-left-right into and out of the foliage to dislodge the fruit.
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