In my last column we talked about the harvest, as being the first step in the wine process in the fall. Obviously, if vines are not planted then no wine will be produced. Once the grapes are picked by hand or machine, they need to be crushed. Crushing is not to be confused with pressing. When grape berries are crushed, the aim is the break the skin and allow the juice and all the contents to escape. While pressing involves separating the juice from skins, seeds, and stems. One technique which combines both crushing and pressing, was used by our nonni in the good old days….. stomping the grapes!
When grapes are crushed, the decision whether to de-stem or not, takes place. Basically, you are separating the grape from its stem. De-stemming will take place at the harvest if machine harvesting is used, or at the winery with a machine that combines both, called a crusher-destemmer. (See photo) The grapes are first crushed by this machine than destemmed. Most red wines today are de-stemmed. Leaving the stems with the grapes during fermentation will introduce green and herbaceous flavours to the finished wine. The stems contain compounds which will lead to bitterness. Even some winemakers in regions which are very traditional, such as Burgundy in France, have been de-stemming since the 1980’s. Burgundy’s principal grape pinot noir, has less tannins than other red grapes. However, many winemakers in Burgundy know that the use of stems during fermentation would increase the tannins in their wines. Like most things in winemaking, it’s a question of tradition versus modernity.
We know that red wine get its colour from fermentation with the skins. Whites on the other hand are separated from their skins and pressed before fermentation. This is to avoid any tannins from the stems, skins or seeds. Therefore it is not necessary to de-stem whites since the juice will be separated from all other materials before fermentation. Reds on the other hand undergo primary fermentation with the grape skins, seeds and juice before being pressed.
The process of crushing the grapes will release most of the liquid from the grape. However, to get the last few remaining drops of liquid, pressing the grapes is also necessary. Presses act by positioning the grape skins or whole grape clusters between a rigid surface and a moveable surface and slowly decrease the volume between the two surfaces. Today, winemakers can control the amount of pressure when pressing the grapes. There are 2 wines presses that are used today: batch and continuous. With the batch press, the grapes are loaded into presses which can be hand operated or presses which use computerized membranes. Once the juice is released, the leftover material, called the “cake” or pomace, (skins, seeds and stems) is removed from the press (Sometimes, the cake is broken up and pressure reapplied before it is removed. Many of our fathers in home winemaking do this, including mine.) Then, another “batch” of grapes is loaded into the press and the process is repeated. A type of batch press we are all familiar with is the basket press. (See photo) This is the one that most of our fathers use. It consists of a pressing plate on top of 2 flat wooden half-moon blocks within a “basket” consisting of vertical wooden slats. These slats in turn are on top of a metal base and draining pan. The vertical slats allow the juice to escape while trapping the pomace. Within the “basket” you have a stationary threaded shaft with a ratcheting head which presses the half-moon blocks over the plates which presses the grapes. The advantage to these types of presses is the gentle treatment of the grapes. The disadvantage is time. The loading and pressing of the grapes and the removal of the pomace is time consuming. Many of you know what I am talking about. You will recall the long hours pressing the grapes with your dad. That click clack sound of the press is something I am sure we are all familiar with!
With continuous presses, “a helical screw (such as an auger) or belt that transports the grapes from a feed in across a cylindrical screen or between air pressured filled pads that presses the grapes, compacts the cakes and then removes the cake through an output all in one continuous operation.” (R. Boulton, V. Singleton, L. Bisson, R. Kunkee Principles and Practices of Winemaking pgs 91-95)
The first juice that is released after the crush is called the free-run juice. Given the volume of liquid that is released this juice tends to have more complex properties than the juice obtained after the grapes are pressed called the press juice. Because of this, wine can be made using only the free-run juice. In fact many white wines are made today using free-run juice. Obviously most winemakers use both juices to increase the amount of final wine. Typically press juice adds 20% to the volume of total wine made. This October, I made 2 small batches of red wine. One using the free-run juice only and the second batch using both free-run juice and press juice. I will let you know the differences in a few months!
Grazie e salute!
By Domenico Cellucci