To press or not to press? That is NOT the question. Rarely does anything in winemaking have an absolute however pressing is one of the few. Grapes must be pressed at some point in the process to release the juice or wine. However, even though grapes must eventually be pressed, it is the when, how and how much that are open to interpretation. What seems deceptively simple on the surface, when explored, reveals a maze of different combinations and outcomes.
White wines are generally pressed prior to fermentation. When pressing prior to fermentation several things must be considered. If the fruit is in excellent condition, hand-picked, and still intact, whole cluster pressing may be the best option. This can be accomplished quite nicely with a basket press or with a more modern bladder press. The latter has the added benefit of being able to control the amount of oxygen that comes in contact with the juice. In the case of New Zealand Sauvignon Blanc, this is a critical part of the style. By completely blanketing the press itself and the press pan with dry ice (CO2) the juice can be kept in a reductive state (non-oxidative). This, in turn preserves the high toned thiol compounds (think grapefruit and passion fruit aromas) that define this style post fermentation. The recent rise of orange wines with skin contact during fermentation are the obvious exception to this rule. For these wines, as well as other white wines where some skin contact is desired, it may be better to destem and lightly crush the fruit. This breaks open the berries and allows the skin and juice to mingle together, resulting in additional flavor compounds and tannins from the skins to be released into the juice prior to pressing.
Red wines are usually pressed during or post fermentation. The timing depends highly on the style of wine that one is trying to create. Earlier pressing during fermentation will minimize tannin extraction and lead to a lighter style with gentle structure while waiting until fermentation has finished will generally result in a fuller bodied, more structured wine. This is, of course, subject to the general characteristics of the grape variety and vineyard. When I was making Cabernet Sauvignon from Lake County, I found that earlier pressing helped control the rather aggressive tannins that the volcanic soils of the area seem to generate. If one can control the tannin extraction throughout the fermentation to allow the wine to go dry on skins without over extracting, the resulting wine ends up being both well-structured and generous without being hard or tough.
The decision of how long to allow grapes to sit on their skins prior to pressing is another important one in the pressing process. In more neutral varieties such as Chardonnay, a small amount of skin contact can add extra palate texture and dimension. However, more aromatic varieties, especially Viognier and Gewurztraminer, tend to have higher tannins in the skins so in these cases additional skin contact could bring in bitterness which will then have to be fined out later through PVPP, Gelatin, or Isinglass treatments. For Rosé, the amount of time the juice spends on skins directly correlates to the depth and intensity of color in the wine as well as the resulting texture on the palate. Depending on the color content (anthocyanin content) of the variety, this time on skins can range from a few hours to a day or more. Red wines which have gone dry on the skins can be pressed immediately or they can be left for extended skin maceration with further integrates the tannins and middle palate texture. Each offers benefits to the final style of the wine but extended skin contact can be somewhat risky since the wine is no longer as protected from spoilage organisms, such as vinegar or lactic acid bacteria, as it was during fermentation.
The pressure at which to press can influence the style of the wine as well as the total volume in terms of wine yield per ton of grapes. In Traditional Method Sparkling wine production pressing is one of the first critical steps in defining the character of the final wine. Particularly in the cases where red grapes such as Pinot Noir or Pinot Meunier are being used, the time on skins prior to pressing is of the upmost importance. Grapes must be pressed quickly to avoid color or tannins from bleeding into the juice because these aspects can negatively impact the final wine quality. While bladder presses will generally only go to 2 Bars of pressure, some basket presses will climb up to 5 Bars. On red wines these high pressure press wines can be extremely interesting with oily textures and thickly structured palates. In general, high pressures such as this only represent 1% or less of the yield of a ton of fruit but it can add interesting elements to the total wine when used.
Press cuts are another point of differentiation for wine styles. A press cut is a separation of juice or wine during the pressing process. For wineries with old style screw presses, the option of press cuts does not exist, however wineries with basket presses or more modern bladder or screw presses have the option to take as many cuts as they would like. Many Champagne houses only use the first gentle pressing, called free run juice, and perhaps part of the light press but usually they do not use the heavier pressing juice to minimize undesirable roughness in the juice. The defining points between free run, light press, and heavy press depend highly on the variety, the style of press used, and the desires of the winemaker. They can be based on pressure, time in the cycle, yield, pH, which climbs with increasing pressure, taste, or some combination of these.
While all wines have been pressed at some point, the differentiation in style and quality comes from the creative combination of the decisions made from the options available. With so many different variables, it is understandable how two winemakers with similar fruit from the same region can make radically different wines.
Originally written for and published on Snooth.com.