Mastering MOG: Field Strategies for Impeccable Harvest Quality

The Costly Reality of MOG Contamination

Vineyard managers understand the immense pressure of harvest season, a period where meticulous planning meets the unpredictable realities of the field. A pervasive and often underestimated challenge during this critical window is the management of Material Other than Grapes (MOG). You know the drill: truckloads arrive at the crush pad, only to be scrutinized for everything from leaves and petioles to insects and unripe berries. This isn't merely an aesthetic issue; it's a significant financial drain and a threat to wine quality.

The immediate cost impact of unmanaged MOG is substantial. Wineries incur increased labor and equipment costs for sorting, which can slow down processing, bottleneck operations, and lead to overtime expenses. Excessive MOG can damage crush pad machinery, requiring costly repairs or downtime. More critically, high levels of MOG can introduce undesirable flavors, aromas, and phenolic compounds into the must, compromising the final wine's quality, potentially leading to lower market value or even rejection of the fruit lot. This ripple effect can damage long-term relationships with wineries and impact your vineyard's reputation for delivering premium fruit.

Defining MOG and Understanding Winery Specifications

MOG encompasses any material delivered with the grapes that is not a mature, healthy grape berry. This includes, but is not limited to, leaves, petioles, stems, rachises, cluster fragments, unripe or rotten berries, insect debris, soil, rocks, and foreign objects. Effective MOG management begins with a clear understanding of what constitutes unacceptable material and, more importantly, precise communication with your winery partners.

Crucial Winery Communication and Specifications

Before harvest commences, establish direct communication with each winery's winemaking team. Obtain their exact specifications for fruit delivery, not just for Brix and pH, but specifically for MOG tolerance. These specifications are dynamic and can vary significantly between wineries and even between different tiers of wine production within the same winery. Document these details meticulously.

Key Insight: Proactive communication about MOG tolerance is as critical as discussing Brix and pH targets. Confirm these parameters for each block and destination.

Pre-Harvest Field Preparation: Laying the Groundwork

MOG management doesn't start at harvest; it begins weeks or even months prior. Strategic vineyard practices can significantly reduce the potential for MOG contamination.

1. Canopy Management for Clean Harvest

• Targeted Leafing: Perform leaf removal in the fruiting zone 2-3 weeks before veraison. This allows for sunlight exposure, promotes even ripening, and dries out the fruiting zone, reducing the likelihood of mold. Crucially, it creates a cleaner picking environment for both manual and mechanical harvesting. Aim for 50-70% dappled sunlight exposure on clusters.
• Shoot Positioning: Ensure shoots are properly positioned and tucked to prevent entanglement with clusters, which can lead to excessive petioles and leaves being picked.
• Weed and Cover Crop Management: Keep rows and under-vine areas clean of tall weeds or cover crops that could be picked up by mechanical harvesters or interfere with manual pickers. Mow cover crops to 4-6 inches a week before harvest.

2. Equipment Readiness and Sanitation

• Harvester Maintenance: For mechanical harvesting, ensure all moving parts are in good repair. Check shaker rods, collection plates, and especially the fan and cleaning systems. Calibrate fan speeds and shaker frequencies.
• Picking Bins/Totes: All bins, gondolas, or macro-bins must be thoroughly cleaned and free of debris, dust, or residual material from previous harvests. Contamination from dirty bins is an easily avoidable MOG source.

Precision Picking: Manual Harvest Strategies

Manual harvesting offers the greatest control over MOG, but only with proper training and vigilant supervision. The human element is both the greatest asset and potential liability.

Step-by-Step Crew Training and Management:

1. Pre-Harvest Briefing: Gather the crew before they enter the block. Clearly explain the winery's MOG expectations. Show them examples of acceptable and unacceptable clusters/berries.
2. Demonstration and Practice: Supervisors must demonstrate the correct picking technique: cutting above the cluster, gently placing it in the bin, and inspecting for leaves, petioles, and rotten berries. Allow new pickers to practice under supervision.
3. Individual Inspection Protocol: Instruct pickers to quickly inspect each cluster before placing it in the bin. Emphasize removing attached leaves, stems, or rotten berries. For high-value blocks, a zero-tolerance policy for obvious MOG might be enforced.
4. Bin-Side Quality Control: Assign dedicated quality control personnel to inspect bins as they are filled. They should perform spot checks and provide immediate feedback to pickers. A typical target is to check 1 in 5 bins or 10% of each picker's output.
5. Troubleshooting & Feedback: If MOG levels increase, identify the specific pickers or sections of the vineyard contributing to the problem. Provide immediate, constructive feedback and re-training.

Example scenario (hypothetical): A new picking crew, despite initial instructions, consistently delivers bins with an estimated 2-3% MOG (primarily leaves and small stems). A supervisor implements a mandatory 15-minute re-training session, demonstrating proper cluster handling and MOG removal. Within two hours, subsequent bin checks show MOG levels dropping to an estimated 0.5-1.0%, demonstrating the direct impact of hands-on correction.

Safety Considerations for Manual Crews:

• Ensure proper hydration and shade breaks.
• Provide safety equipment: gloves, eye protection, appropriate footwear.
• Train on safe use of picking knives/shears and proper lifting techniques for bins.

Optimizing Mechanical Harvesting for MOG Reduction

Mechanical harvesters are highly efficient but require precise setup and operation to minimize MOG. The goal is to maximize berry separation while minimizing leaf and stem inclusion.

Step-by-Step Mechanical Harvester Operation:

1. Pre-Pass Inspection: Before starting, walk the row. Note canopy density, vine vigor, and any ground debris. This informs initial machine settings.
2. Initial Machine Calibration: Based on grape variety, ripeness, and canopy density, set initial parameters:
   • Shaker Frequency: Typically 180-220 beats per minute (bpm). Start lower and increase as needed to detach berries.
   • Shaker Stroke: Adjust to maximize berry removal without excessive vine damage or MOG.
   • Fan Speed: Critical for MOG removal. Start with a moderate speed (e.g. 60-75% of maximum) and adjust up or down. Too low, and leaves remain; too high, and berries can be lost.
   • Ground Speed: Typically 1.5-2.5 mph. Slower speeds allow more time for berries to detach and for cleaning systems to work effectively.
3. In-Field Adjustments: After harvesting the first few rows, stop and inspect the collected fruit. Look for:
   • Excessive MOG: If too many leaves/stems, increase fan speed or adjust shaker settings.
   • Berry Loss: If berries are left on the vine or ejected, adjust shaker frequency or ground speed.
   • Vine Damage: If excessive, reduce shaker intensity or ground speed.
   Make small, incremental adjustments and re-evaluate.
4. Monitor Conditions: Harvest in dry conditions if possible. Morning dew can cause leaves to stick to berries, increasing MOG. If harvesting damp fruit, consider slightly higher fan speeds.

Example scenario (hypothetical): Harvesting a high-vigor Cabernet Sauvignon block, the initial pass with a mechanical harvester (e.g. a Pellenc or Braud unit) yields fruit with an estimated 1.5% MOG, largely due to small leaf fragments. The operator, observing this, increases the primary fan speed from 65% to 75% and slightly reduces ground speed from 2.2 mph to 1.8 mph. A subsequent inspection of the fruit reveals MOG levels have dropped to an estimated 0.6%, demonstrating the effectiveness of in-field adjustments.

Post-Harvest Field Checks and Data Collection

The work isn't done when the last bin leaves the field. Post-harvest analysis is vital for continuous improvement.

• Bin Inspection: Conduct final visual inspections of fruit in bins before they depart for the winery. This is the last chance to identify and potentially mitigate MOG issues.
• Winery Feedback Loop: Maintain open communication with the winery during and after fruit delivery. Ask for specific feedback on MOG levels and quality. Document any instances where MOG was flagged.
• Data Tracking: Track MOG incidents, crew performance, and mechanical harvester settings block by block. Platforms like VinoBloc can assist vineyard managers in logging harvest data, MOG percentages, and other critical metrics, enabling analysis for future harvests.

Actionable Next Steps for Vineyard Managers

To proactively manage MOG and ensure superior fruit quality for the upcoming harvest, consider these immediate actions:

1. Review and Document Winery Specs (Timeline: Immediately, before harvest planning): Contact all receiving wineries to re-confirm or establish precise MOG tolerance levels and other critical fruit specifications for each block. Create a master document accessible to all harvest supervisors.
2. Develop a Comprehensive Crew Training Program (Timeline: 2-4 weeks pre-harvest): Design a detailed MOG-specific training module for all manual picking crews, including visual aids, hands-on demonstrations, and a clear feedback mechanism for supervisors.
3. Calibrate and Test Harvester Settings (Timeline: 1 week pre-harvest): For mechanical operations, perform dry runs or test passes in a representative block to fine-tune shaker frequencies, fan speeds, and ground speeds. Document optimal settings for different blocks and varieties.
4. Implement a Real-time Field Quality Control System (Timeline: Throughout harvest): Assign dedicated personnel to conduct continuous spot checks of fruit in bins (both manual and mechanical) and provide immediate corrective feedback. Utilize a system for logging MOG observations and adjustments.

Success Metrics:

Measure success by tracking:

• Reduction in reported MOG percentages from wineries.
• Fewer instances of fruit rejection or quality penalties.
• Improved feedback and stronger relationships with winery partners.
• Increased efficiency at the crush pad due to cleaner fruit.

By implementing these detailed strategies, vineyard managers can significantly reduce MOG, elevate fruit quality, and solidify their reputation as providers of premium grapes, ensuring a smoother, more profitable harvest for all involved.