**Historical Evolution of Pressing Methods:**
– Basket presses used since the Middle Ages, evolving from human feet to mechanical presses.
– Development of sack presses by Ancient Egyptians and wooden presses by Greeks and Romans.
– Adoption of basket presses by nobility and the Catholic Church in the Middle Ages.
– Transition to mechanical pressing in the 17th and 18th centuries for heartier wines.
– Introduction of horizontal pressing methods in the 20th century, replacing vertical basket presses.
**Juice Extraction and Differentiating Characteristics:**
– Pressing extracts 30-40% of juice with distinct characteristics from free-run juice.
– Free-run juice constitutes 60-70% of available juice and does not require pressing.
– Pressed juice may have higher pH, volatile acidity, and phenolics.
– Winemakers often separate free-run juice and pressed wine for blending.
– Typical wine volume comprises 85-90% free-run juice and 10-15% pressed juice.
**Modern Pressing Techniques and Technology Advancements:**
– Application of pectolytic enzymes for breaking down cell walls and aiding juice release.
– Filtering decisions based on the amount of suspended solids in pressed juice.
– Introduction of enclosed tank presses to reduce exposure of grape must to air.
– Evolution of pressing technology for improved efficiency, extraction, and wine quality.
– Classification of wine presses into batch and continuous types, with advancements in continuous presses.
**Varieties of Presses and Their Operational Characteristics:**
– Description of batch presses involving different types like basket, moving head, bladder, and membrane presses.
– Operational steps in batch presses, including filling, applying pressure, and emptying.
– Benefits of continuous presses for high-volume wine producers with minimal labor involvement.
– Transition from screw presses to membrane presses in the wine industry.
– Types of continuous presses like screw, impulse, and belt presses with trade-offs between volume and quality.
**Impact of Pressing on Wine Characteristics and Production Techniques:**
– Influence of pressing method on wine color, body, aroma, and aging potential.
– Differences between free-run and pressed juice in acidity, phenolics, and suspended solids.
– Utilization of whole-cluster pressing for delicate wine production and phenolic control.
– Significance of press fractions in affecting wine characteristics and stability.
– Historical background of press fractions, as seen in Champagne traditions and winemaking references.
In winemaking, pressing is the process where juice is extracted from the grapes with the aid of a wine-press, by hand, or even by the weight of the grape berries and clusters. Historically, intact grape clusters were trodden by feet but in most wineries today the grapes are sent through a crusher/destemmer, which removes the individual grape berries from the stems and breaks the skins, releasing some juice, prior to being pressed. There are exceptions, such as the case of sparkling wine production in regions such as Champagne where grapes are traditionally whole-cluster pressed with stems included to produce a lighter must that is low in phenolics.
In white wine production, pressing usually takes place immediately after crushing and before primary fermentation. In red wine production, the grapes are also crushed but pressing usually doesn't take place until after or near the end of fermentation with the time of skin contact between the juice and grapes leaching color, tannins and other phenolics from the skin. Approximately 60-70% of the available juice within the grape berry, the free-run juice, can be released by the crushing process and doesn't require the use of the press. The remaining 30-40% that comes from pressing can have higher pH levels, lower titratable acidity, potentially higher volatile acidity and higher phenolics than the free-run juice depending on the amount of pressure and tearing of the skins and will produce more astringent, bitter wine.
Winemakers often keep their free-run juice and pressed wine separate (and perhaps even further isolate the wine produced by different pressure levels/stages of pressing) during much of the winemaking process to either bottle separately or later blend portions of each to make a more complete, balanced wine. In practice the volume of many wines are made from 85 to 90% of free-run juice and 10-15% pressed juice.