Grape presses: Turning grapes into wine

moderne industrielle Traubenpresse
© Scharfenberger GmbH & Co.KG

Grape presses, also called wine presses, feature sophisticated technology. To this day they remain a key piece of equipment for any winery, provided the winery receives the grapes itself and oversees the wine production process right from the very start of the process chain. Presses represent a huge investment, so a purchase needs to be well thought out and consider the specific requirements of the business. 

Although modern grape presses work differently and use different technology than their predecessors, the original versions represent some of the oldest pieces of equipment ever used in the history of humanity. The collecting tanks and bases of presses used to extract juice from grapes and other fruit were used early in the history of humans in Mesopotamia and Egypt and later everywhere the Greeks, the Phoenicians and, subsequently, the Romans settled. Egyptians used to press grapes between cloths and were able to extract relatively pure juice this way. The Romans used presses with massive oak beams to do the work — a standard design favored until the modern era.

Today, grape presses are high-tech devices that treat grapes as gently as possible and feature monitoring sensors and digital connectivity with the entire production process both upstream and downstream. Everything in this process has to be perfectly coordinated: grape loading, conveyor systems, pump systems and the grape crusher as well as the press and the interim storage containers for further processing the extracted must.

Winery operations are experiencing an ongoing drop in their numbers while at the same time cultivating larger areas and having larger grape harvests to handle in the fall. As a result, demand for smaller presses with a volume of 20 or 40 hectoliters is falling. Investments in replacing old presses and new investments tend more toward covering midrange sizes with a volume of between 60 and 80 hectoliters. Grape presses at larger wineries and winegrowers’ cooperatives are even capable of accommodating volumes of over 400 hectoliters in a single operation.

Trauben an der Rebe vor der Traubenpresse
© Pixabay/ User: congerdesign

Grape presses: Long idle periods due to short usage periods

Unlike many other pieces of equipment used in wine production, grape presses are only needed for a relatively short period each year. Most of the time, these gargantuan machines are carefully packed away and stored in the grape loading stations, in driveways or in cellars and are tested again later to ensure they are still in good working order just a few weeks before the fall harvest. Many of the parts found in grape presses are extremely solid and practically indestructible, including the bearings, the solid stainless steel drums, cover plates and channels. However, other parts, such as the electronics, tubes and pressure membranes, are subject to wear and aging. This makes it a good idea when purchasing a press to ensure it’s made from solid materials and to always secure a large supply of replacement parts.

Before the grapes enter the wine press they need to be harvested. From an etymological perspective, the German words Herbsten (grape harvest) and Herbst (fall) share their origins with the English word “harvest.”

Electric motors, which are idle for over 10 months of the year before then being put back into operation for just a few weeks and expected to achieve full capacity, have a particularly difficult time coping with this schedule. Contact parts end up covered in oxidized layers and sometimes it’s a wonder such machines ever work again after such long idle periods.

Tough requirements for reliability, operability and cleaning

The list of requirements grape presses need to meet is short and sweet: Presses need to be sturdy, well made and as easy to fill and empty as possible; cleaning them also needs to be easy and reliable. In addition, the grapes themselves need to be treated as gently as possible: After all, users want to extract the juice from ripe grapes and not the acrid tart plant extract from grape stalks, stems and tart skins. For this reason, the metal sheets that come into contact with the grapes are now usually glass bead blasted with fine abrasives and specially polished or satin finished so the surface is as smooth as possible.

Smooth surfaces are also important for cleaning, a critical issue now that fall temperatures are typically much warmer than in the past and pockets of bacteria can easily build up on any grape or plant remnants. This makes hygiene a key issue in winemaking, which is why modern grape presses boast new cleaning systems that can also feature in closed presses. The requirements of modern oenology (the science of winemaking) are playing an increasingly important role in terms of the design and equipping of wine presses: whole-cluster pressing and maceration require greater press volumes. The time for breaking up and loosening the pomace (press cake) should be as short as possible.

Nahaufnahme einer Traubenpresse
© Pixabay / User: Gallila-Photo

Pneumatic wine presses are the name of the game these days

The principle behind today’s very popular membrane presses is the same for pretty much all manufacturers and models. Using a membrane attached to one side of the drum cage, grapes are squeezed against a slotted cage or, in the case of closed presses, against internal juice channels. These are self-cleaning and function like a drainage system.

One company that has adopted a different approach is Willmes: Its wine presses also have membranes attached to both sides and squeeze the grapes against vertical juicing areas inside the press. Willmes states that they function like a natural drainage system, which always results in the same short juice paths that allow the juice to drain more directly and quickly

KVT is another company with a different system: For its presses, the company uses a fully slotted stainless steel cylinder against which a membrane centrally attached around the axle of the drum squeezes the must. The juice then flows through the entire area of the press cage and into the press pan.

© Willmes GmbH

Auxiliary equipment expands the range of oenological options

If reductive winemaking is preferred, inert gas technology with nitrogen blanketing is used. This technology can be designed with or without recovery of the used nitrogen. Even the collecting vessel and subsequent storage tank can be filled with nitrogen so that pressing can be carried out with almost no oxygenation. Whole-cluster pressing, which is now used for some grape varieties and base wine types, can be carried out by almost all press models. If filling volumes change, different control programs need to be available: from prejuicing with prepressing stages and pressing stages with increasing levels of pressure through to conclusive final pressure stages.

It is also important for many users to be able to cool the grapes as soon as the wine production process starts, which is why most manufacturers sell cooling devices in the form of accessories. Cooling the grapes right from the start can be advantageous given the now often summery temperatures experienced during the harvest season in the fall. As wine presses are considered long-term capital goods in the winemaking industry, almost all manufacturers also sell used, second-hand grape presses, which, following a complete overhaul, often provide an affordable option for initial investors.   

Dr. Hermann Pilz

Dr. Hermann Pilz has been in charge of the trade magazine WEINWIRTSCHAFT as chief editor for over 20 years. He loves writing about many different topics of the wine and spirits industry.