Destemming grapes is a crucial step in the winemaking process, and it involves the removal of the grape berries from their stems. This process is also known as “de-stemming” or “racking.” When grapes are harvested and brought into the winery, they are usually in clusters, with several berries attached to a stem. These stems contain a higher concentration of astringent tannins, which can negatively impact the quality and taste of the wine.
To begin the destemming process, the harvested grape clusters are loaded into a destemmer machine. This machine gently separates the berries from the stems, using rotating paddles or rotating cylinders with holes that allow the berries to be separated while the stems are retained. The berries are then usually crushed or pressed to extract the juice, which will eventually become wine.
Destemming is an essential step for several reasons. Firstly, it helps to reduce the level of tannins in the final wine. Tannins are naturally occurring compounds found in grape skins, seeds, and stems, and they contribute to the structure and mouthfeel of the wine. However, excessive tannins can make the wine bitter or astringent, overpowering the fruit flavors and aromas. By removing the stems, winemakers can control the amount of tannins that are introduced into the wine, resulting in a more balanced and enjoyable final product.
Secondly, destemming allows for better control over fermentation. During fermentation, yeast converts the grape sugars into alcohol, and the presence of stems can interfere with this process. Stems can act as a physical barrier, preventing the yeast from coming into contact with the grape juice. By removing the stems, winemakers ensure that the yeast can fully access the juice, leading to a more efficient and complete fermentation.
Moreover, destemming can also help to improve the overall quality of the wine. As the stems contain fewer desirable flavors compared to the grape berries, their removal can contribute to a cleaner and more focused flavor profile. Additionally, stems can sometimes harbor unwanted microbial organisms that may negatively affect fermentation or lead to off-flavors in the wine. By separating the berries from the stems, winemakers minimize the risk of such microbial contamination.
It is important to note that not all winemakers choose to destem their grapes. Some prefer to include a portion of the stems during fermentation, as they believe it adds complexity and structure to the wine. This technique, known as “whole-cluster fermentation,” is particularly common in certain wine regions and with specific grape varieties. However, it requires careful monitoring and management to ensure the desired results, as the stems can have a significant impact on the final wine's character.
In my own experience as a sommelier and brewer, I have witnessed the effects of destemming on wine firsthand. I have tasted wines made from grapes that were destemmed versus wines made from grapes that were not destemmed. The difference in tannin levels and overall balance was noticeable. Wines made from destemmed grapes tended to be smoother, with more pronounced fruit flavors and a more harmonious mouthfeel. On the other hand, wines made with stems included often displayed more astringency and a slightly herbaceous or vegetal character.
Destemming grapes is an important step in winemaking that involves removing the grape berries from their stems. This process helps to reduce astringent tannins, improve fermentation efficiency, and enhance the overall quality of the wine. However, the decision to destem or not is ultimately a winemaker's choice, as it can have a significant impact on the final character and style of the wine.