How to press grapes to make wine: Grape pressing

Grape pressing refers to the process by which the must, or juice, is extracted from the fruit. The solid part of the grape (skins, seeds, and scrapes) is separated from the liquid part (the juice).  

This step takes place shortly after harvest, just after the crushing, so it is one of the very first phases in winemaking and is decisive in determining its quality. It is important not to confuse squeezing with pressing. Squeezing is what is done to break the grape to release the juice, while pressing extracts the liquid more intensively. 

Thanks to the pressing process, several things are achieved: 

Pressing grapes is something that can be done in different ways. In the past, winemakers would squeeze the fruit with their hands or step on it with their feet. Luckily, advances in the sector made it possible to quickly replace these rudimentary techniques with others that are more comfortable, simple, and hygienic. In this context, grape pressing for wine takes on special relevance.  

Did you know that remains of these wine-squeezing and pressing tools have been found that are 2600 years old? You can see this is an invention with a lot of history and, although there have been some for all tastes and uses, they are all based on the same thing: exerting controlled pressure to release the liquid from the fruit. This is possible thanks to Pascal's principle, which states that the pressure that is exerted on a fluid spreads throughout the substance equally. As you can see, physics is a key aspect in winemaking. 

With regard to grape pressing for wine, we can highlight four types of presses, which we will list below.  

The spindle press, or basket press, is one of the most traditional pressing systems used in winemaking. Its design is simple yet effective. It consists of a cylindrical basket, usually made of wood, where the grapes are placed, and a central spindle that, when rotated, exerts pressure on wooden blocks that crush the fruit to extract the must. The resulting liquid drains through an opening in the base and into a container.  

In this type of press, force must be exercised manually. This, together with its limited capacity, makes it an option only used in artisanal or homemade productions. 

Pneumatic presses use compressed air to inflate a membrane that gently presses the grapes against a perforated cylinder, allowing a controlled and homogeneous extraction of the must. In addition, they allow you to adjust the pressure in each case as needed. 

Pneumatic presses can be made into two types: closed and open. The former are the most common and oxidize the must more efficiently. The latter offers more speed and can handle a large volume of production. 

As we have seen, there are different pressing systems, so choosing one type or another will depend on several factors, such as the volume of work or the type of wine you want to produce. That's right; each wine requires its own technique to ensure the result is completely satisfactory. The basic steps of pressing grapes to make wine are listed below. But first, we want to share with you some basic factors that will determine the success of this operation. 

It is important to note that abruptness and violence should not be abused since an intensity that is too high could harm the result. It should also be clarified that the type of pressure exerted is not directly related to the pressing time. Contrary to what common sense would suggest, high pressure does not shorten the duration of this process; it will only cause the drainage channels to clog more quickly. 

It is also necessary to control the temperature throughout this phase. If temperatures rise too high, they can start unwanted fermentation. 

Finally, we must not forget about the regular maintenance and hygiene of presses and other equipment. It is essential so that no pollution or contamination occurs. 

Normally, white wine is pressed right after the harvest. After destemming, where the scrape is separated from the grape, the resulting raw material is introduced into the press to start the magic of the process.  

In the production of white wine, pneumatic presses are usually used. These machines offer great precision and efficiency, which is very important when it comes to controlling tannins and other compounds that will determine the character and quality of the wine. Another system used for this purpose is the mechanical press.  

White wine usually requires crush pressing. This is a method where the pressure exerted on the white grape is very gentle and, therefore, slower. This is the only way to prevent bagasse from losing its anthocyanins.  

The pressing of red wine follows guidelines quite different from those we have already seen. This phase can occur directly after the destemming and crushing of the grapes. If this happens, the bagasse is preserved to accompany the must in the maceration process. The reason is simple: the skin of the grapes is where the tannins and aromas are concentrated. Pressing can also take place after the fermentation of the wine.  

Standard pressing is usually chosen for red wine. The reason is that, in general, red wines will require greater pressure to unleash their full potential. For this purpose, hydraulic and mechanical presses are mainly used. Pneumatic presses are also used to produce high-quality red wines. 

If you have come this far, you will have realized the importance of grape pressing in the winemaking process. The quality and characteristics that we find in the final wine that we can enjoy every day at our table depend on it. For everything to go well and the extraction of the must to take place efficiently, there are many factors that must be taken into account, such as choosing the right type of press or applying the right pressure.

Thus, technology, physics, and science are put at the service of the art behind winemaking to surprise us with products as exquisite as those you can buy in our online wine store.