Ulrich Willmes
The Press as a “Quality Gate”
Ten Practical Rules for Preserving the Grapes’ Potential in the Must
The press is the critical juncture between vineyard and cellar. It is where it becomes clear how much of the grapes’ quality potential actually reaches the must. Anyone seeking to work in the premium segment with as few corrective interventions and additives as possible—and anyone aiming to produce wine as cost-effectively as possible—must plan precisely before the first pressure stage.
Pressing Does Not Begin in the Press House
Pressing is not an isolated machine operation. The condition of the grapes, harvest timing, outdoor temperature, weather, transport containers, waiting time, and route to the press collectively determine the quality that can ultimately be extracted. Even a good press cannot turn damaged, overheated, or microbiologically compromised grapes back into intact fruit.
The most important practical consequence is this: The vineyard, harvest logistics, grape reception, and pressing must be planned as one continuous process. What matters is not the maximum rated capacity of a single machine, but a steady flow of material without long delays or unnecessary transfers. Anyone aiming to reduce SO₂ additions depends on especially gentle processing and rigorous control of oxygen exposure. Good process management can reduce the need for protective and corrective measures, but it cannot replace targeted enological safeguards.
Synchronize Harvest and Press Capacity
The number of harvest workers or mechanical harvesters, transport capacity, and the realistic length of a press cycle must be aligned. If more grapes arrive than can be processed, delays result. If the press is too large for the actual daily throughput, it can take too long to accumulate a full load. Both situations increase the risk of oxidation, unwanted microbial activity, and hygiene problems.
A useful planning guideline is this: With hand harvesting, the press should ideally be fully loaded within three hours after the first grapes are harvested; alternatively, the fruit should be held in cold storage until processing. With machine harvesting, the press should be filled within one hour. These time windows are not universal standards. At high temperatures, with compromised fruit, or for varieties particularly prone to oxidation, schedules must be tighter.
Practical recommendation: Before harvest, do not calculate only throughput in tons per hour. For each lot, also account for arrival time, start of loading, planned program, unloading, cleaning, and available must tanks. A small time buffer is useful; a backlog of grapes generally is not. Holding grapes before processing is advisable only when macerating aromatic varieties or processing chilled fruit.
Protect Grapes During Transport
The more grapes are compacted, crushed, or warmed in a container, the sooner juice release, oxidation, and microbial changes begin. Transport must therefore suit the grape variety, harvesting method, temperature, and intended wine style. Grapes that are delicate or harvested under warm conditions benefit from smaller, well-ventilated containers and short transport distances. Large containers make sense only when compaction and juice pooling can be reliably avoided. In addition, the longer the route, the smaller the transport container should be.
Champagne demonstrates how consistently this principle can be applied to a narrowly defined quality objective: Whole grape clusters are expected to arrive intact at the pressing center, transport crates must quickly drain any released juice, and pressing should begin as soon as possible after harvest. These rules do not automatically apply to every winery, but they underscore the central point: Transport is already part of must extraction.
Loading: Short, Direct, and Gentle
The best route into the press is the shortest. Direct loading or gravity transfer is better for quality than a long sequence of augers, pumps, hoses, and transfers. Every additional length of hose, every bend, every change in elevation, and every abrupt transfer adds mechanical stress. This does not mean that pumps must be ruled out altogether. They should, however, be used only where necessary, with transfer lines that are as short and generously sized as possible and with gentle pumping technology.
The drop height should also be kept as low as possible. During loading, the press drum should not be rotated merely to fit in more grapes. Such distribution or compaction rotations create additional shear forces even before pressing begins and make clean fractionation more difficult later. At most, the press should be rocked gently back and forth to optimize the fill.
Avoid Both Overloading and Underfilling the Press
A press should be loaded in one continuous operation with the intended quantity. Overfilling impedes drainage, lengthens the cycle, and often requires more frequent crumbling. Significant underfilling likewise alters pressure distribution and can cause unnecessarily strong extraction. The goal, therefore, is neither to load as much nor as little as possible, but to remain within the recommended operating range for the specific press.
The implication for investment and harvest planning is clear: A larger press is not automatically a better press. The right capacity is the one that can be operated quickly, fully, and consistently with the actual harvest flow. Capacity planning should therefore be based on representative harvest days.
Allow the Juice to Drain, Then Press with the Flow
Before the first actual pressure stage, the must released during loading needs time to drain. This free-run juice is a distinct fraction and should not be inadvertently blended with later press fractions. Then proceed as follows: Increase pressure slowly and in stages, hold each stage long enough, and monitor must flow. The juice should flow as evenly and continuously as possible. The objective is not the fastest pressure increase, but a consistent flow rate matched to the press’s drainage system.
High pressure is not a mark of quality. As extraction increases, turbidity, phenolic content, acidity, pH, color, and susceptibility to oxidation may change depending on the grapes. An industrial-scale study found that at higher juice yields, pH, turbidity, color index, and phenolic measurements tended to increase, while titratable acidity decreased. The extent of these changes depended on the grape variety and pressing conditions. Higher pressures require more mechanical crumbling.
Crumble Only When the Pomace Cake Requires It
Crumbling is intended to restore drainage through the pomace cake—that is, to reopen drainage paths. It is not an additional grinding step. If crumbling occurs too early or too often, the grape skins and seeds are exposed to greater shear forces. At the same time, decompression and redistribution can release another surge of phenolics and more oxidation-prone must.
Recent studies on Pinot Noir and Pinot Meunier show that marked changes in quality occur not simply at a specific volume of extracted juice, but especially after depressurization and pomace reworking. The practical conclusion: Use crumbling sparingly, then taste and measure with particular care. This effect is especially relevant when the goal is to obtain as much lightly colored juice as possible for Blanc de Noirs.
Separate Must Fractions by Quality, Not Just Quantity
Fractionation is not just for sparkling wine. In still white and rosé wines, free-run juice, early press fractions, and later press juice can also make very different contributions to aroma, acidity, structure, color, and aging potential. Combining these musts immediately means giving up one of the most effective ways to manage quality and select the appropriate must treatment without later corrections.
At a minimum, free-run juice and press juice should be evaluated separately. In the premium segment, several clearly defined fractions are useful, provided sufficient tanks, cooling capacity, and documentation are available. The switching point should be determined not solely by time or volume, but by must flow, taste, turbidity, pH, color, and, where appropriate, dissolved oxygen. Ideally, fraction changes would also be guided by polyphenol content.
Fractionation does not automatically mean discarding later fractions. They may be valuable for a different wine style, separate fermentation, or later targeted blending. The key is to make the differences visible and manageable first.
Choose the Right Program for Every Lot of Grapes
A standard program can provide a reliable starting point, but it cannot replace an enological objective. The press program must be suited to the grape variety, vintage, ripeness and condition, harvest temperature, harvesting method, press type, and desired wine. A sparkling base wine requires different priorities than an aromatic white wine or a color-stable rosé.
This is especially true of automatic or so-called intelligent programs. Many algorithms initially optimize throughput and yield. For premium quality, pressure stages, hold times, pressure compensation, crumbling, and fraction boundaries must be deliberately aligned with the target wine profile. In the interest of quality, the program should be controlled to maintain a consistent flow of must.
Let the Senses Lead—Confirm with Measurements
Regular sampling remains the most important control. Color, aroma, taste, turbidity, and flow behavior often reveal a change in fraction earlier than a fixed time-based program. A tasting glass at the press outlet is therefore just as essential as a well-defined sampling plan.
Measurements of volume or flow rate, turbidity, and pH are particularly useful. For stringent quality requirements, measurements of dissolved oxygen, polyphenol content, and conductivity can provide additional insight. What matters is not having the greatest possible number of instruments, but selecting a small, consistently documented set that actually informs decisions.
Hygiene and Learning Are Part of the Press Program
Spilled must, warm holding areas, and hard-to-reach lines are prime trouble spots. Crates, the receiving area, the press, collection vessels, hoses, and tanks must therefore be cleaned as an integral part of the harvest rhythm. Cleaning is not a break from the process; it is a planned process stage.
Documentation is equally important. Recording the grape condition, temperature, loading time, program, pressure profile, must flow, fraction boundaries, analytical data, and sensory impressions for each lot creates a winery-specific knowledge base. In this way, a good pressing operation becomes a reproducible process the following year.
The 60-Second Harvest Check
The press is the culmination of the work in the vineyard and, at the same time, the starting point for the work in the cellar. Its primary task is not to extract as much juice as possible as quickly as possible. It should reveal the grapes’ quality potential, separate the fractions cleanly, and preserve that potential for further winemaking. This provides the foundation for the best possible economic result.
Scope: These recommendations primarily apply to the direct processing of grapes for white, rosé, and sparkling wine. For red wine, pressing usually takes place only after fermentation on the skins; however, the principles of gentle handling, separate fractions, and sensory and analytical control remain relevant.
Sources
Secondé, Nicolas (2025): The Press and Its Programming: Operating Instructions. L’Enologo, No. 7–8/2025.
Comité Champagne (2024): Cahier des charges de l’appellation d’origine contrôlée Champagne. View source
Comité Champagne: Arrival at the pressing centre. Official overview of gentle pressing and fractionation. View source
Shanshiashvili, G. et al. (2024): Insight the impact of grape pressing on must composition. IVES Conference Series. View source
Marchal, R. et al. (2022): Impact of press fractioning on current and phenolic compositions of Pinot noir and Pinot meunier wines. IVES Conference Series. View source
García-Roldán, A. et al. (2026): Influence of pressing conditions on the chemical composition, oxygen consumption rate and tyrosinase activity of the grape must. OENO One. View source
Shanshiashvili, G. et al. (2025): Extraction of Grape Juice: Impact of Laboratory-Scale Pressing Methods on the Chemical Composition. Beverages 11(1), 23. View source
More about Willmes and Armbruster
Willmes Armbruster deliver integrated grape processing solutions from vineyard-to-cellar, combining leadership in gentle grape pressing with expertise in grape reception, destemming and sorting. Through customized, high-quality systems, we help wineries achieve optimal grape quality, maximum efficiency, and superior juice results at every step.
Developed through a German research initiative with Fraunhofer IOSB, Armbruster Kelterei Technology and Geisenheim University, GrapeSort brings advanced sensor-based sorting into the winery processing line.
Exceptional wine quality starts with the fruit. During harvest, wineries have only a limited time window to remove leaves, insects, stems, mold-affected berries, damaged fruit or berries outside the desired degree of ripeness - without slowing down production or losing valuable grapes.
Developed in partnership with Germany’s renowned research institutions Fraunhofer IOSB and Geisenheim University, Armbruster Kelterei Technology pioneered optical grape sorting based on quality and ripeness parameters. The resulting GrapeSort system seamlessly integrates into the processing line, using fully automated optical sorting technology to ensure that only grapes of the desired quality proceed to the next stage of production rather than relying solely on manual inspection.
After destemming and feeding, berries accelerated on a conveyor and pass through the sorting zone individually and in free flight. This separation is essential: each berry can be detected and evaluated on its own before the ejection system acts.
At the heart of GrapeSort is a high-speed line-scan camera system capturing up to 18,000 images per second. The image data is analyzed in milliseconds according to trained quality criteria such as color, shape, visible defects, foreign material and degree of ripeness. Operators can adjust sorting parameters through an intuitive touchscreen interface, allowing the system to be adapted to different grape varieties, harvest conditions and winery quality goals.
To further improve sorting performance, GrapeSort combines optical inspection with Near Infrared (NIR) technology. By extending inspection beyond visible color, the system can detect dried, damaged or otherwise unsuitable berries that may be difficult to identify through color alone. This combination of visual inspection and NIR-based analysis supports more consistent decisions, especially when grape condition varies during harvest.
Unwanted berries and foreign material - including leaves, stems, insects, mold-affected fruit or berries outside the desired ripeness profile - are removed through 128 precisely controlled high-speed air valves. Because detection and ejection occur while the berries are in free flight, the system removes only selected material and keeps suitable fruit moving smoothly through the process.
For wineries, the impact is both technical and practical. GrapeSort reduces the need for labor-intensive hand sorting, improves product purity, supports repeatable fruit selection and helps cellar teams maintain processing speed during the short harvest window. Most importantly, it gives winemakers greater control over the quality profile of the incoming fruit - one of the most decisive factors for premium wine production.
Key Features
Fully automated optical grape sorting for winery processing lines
Individual berry recognition in free flight
High-speed line-scan camera scanning with up to 18,000 images per second
Sorting by color, shape, visual characteristics, defects and degree of ripeness
Near Infrared (NIR) detection for dried or otherwise unsuitable berries
Precise removal of selected material through 128 high-speed air valves
Intuitive touchscreen operation and adjustable sorting parameters
Reduced manual sorting effort and improved processing consistency
More about Willmes & Armbruster U.S.
Willmes & Armbruster U.S. delivers integrated grape processing solutions from vineyard to cellar, combining leadership in gentle grape pressing with advanced technologies for grape reception, destemming and sorting. Through customized, high-quality systems, we help wineries achieve optimal grape quality, maximum efficiency and superior juice results at every step of their winemaking journey.
ROTOVIB sets a new standard in gentle grape destemming. Its innovative rotary-vibration technology delicately separates berries from stems, preserving fruit integrity and minimizing mechanical stress. The result is maximum grape quality, enabling winemakers to unlock the full potential of every harvest. https://willmes-armbruster.us/products/rotovib
Willmes and Armbruster are strengthening their global partnership with the launch of Willmes Armbruster U.S. – Grape Processing Solutions, a new venture dedicated to the direct representation and support of both product lines. Headquartered in Petaluma, California, the company will support wineries with new projects while providing ongoing service for all existing installations through a dedicated U.S. based sales and service team.
Both brands had been proudly represented throughout North America by Scott Laboratories for more than forty years.
"It has been an honor to represent Willmes and Armbruster and collaborate with their teams for the past four decades. We will continue to champion their brands, having seen firsthand their dedication to quality and innovation. Our customers are in excellent hands with this new investment in the North American market.”
— Steve Clattenburg, President, Scott Laboratories
Willmes Armbruster U.S. will launch operations under the leadership of industry veteran Damon Dudley, previously General Manager of Scott Laboratories’ Equipment Division.
"This strategic investment underscores our long-term commitment to the U.S. market. Building on decades of trusted partnership, we gratefully acknowledge Scott Laboratories and will continue delivering exceptional service and innovative technology to wineries across North America.
— Ulrich Willmes & Christian Armbruster, President and CEO
More about Willmes and Armbruster
Willmes Armbruster deliver integrated grape processing solutions from vineyard-to-cellar, combining leadership in gentle grape pressing with expertise in grape reception, destemming and sorting. Through customized, high-quality systems, we help wineries achieve optimal grape quality, maximum efficiency, and superior juice results at every step.