Chapter 4

Pressing-Clarification of White Grape Must

(book excerpts)

In white wine production, pressing of musts or whole grapes takes place immediately after destemming and crushing, if needed. In red wine production, the grapes are destemmed and crushed but pressing doesn’t take place until the end of fermentation. White wines are fermented off the skin, therefore they don’t display red/black pigments and have a significantly lower concentrations of tannins. As for red wines, fermentation occurs in a must which contain skins, pips, and other solid parts. That’s why red wines differ so much from whites in terms of color and tannin content, which are extracted from the skins during fermentation. After pressing the juice is clarified to remove suspended solids from pressed juice prior to fermentation. Clarification can enable a more efficient fermentation, resulting in a wine with cleaner and fruitier aromas as well as reducing the danger of hydrogen sulfide (H2S) formation. Common juice clarification methods include natural settling in stainless-steel tanks in which solids fall to the bottom of the tank by gravity, aided by the addition of pectinolytic enzymes, and clarifying agents such as bentonite, gelatin, and silica gel. Other clarification methods used to separate suspended solids from juice include flotation and centrifuging technologies. At this stage the must is ready for alcoholic fermentation—a crucial moment in the transformation process of must to wine.

Click on the following topics for more information on pressing and clarification of white grape must.

Topics Within This Chapter:

  • Drainers
  • Static Drainer
  • Continuous Drainer
  • Pressing the Grape Must
  • Whole-Cluster Pressing
  • Sulfur Dioxide Additions
  • Oxidation of Juice
  • Passive Oxidation
  • Hyper-Oxidation
  • Microbiological Risks
  • Sensory Effects of Must Oxidation
  • Blending
  • Wine Grape Presses
  • Basket Press
  • Advantages and Disadvantages
  • Capacity
  • Reds versus White Varieties
  • Options
  • Moving Head Press
  • Advantages and Disadvantages
  • Membrane Press
  • Press Operation
  • Membrane Configurations
  • Continuous Screw Press
  • Grape Must Clarification
  • Clarification Methods
  • Natural Settling
  • Flotation
  • Centrifuge
  • Enzyme Treatment
  • Bentonite Fining
  • Clarification Affect on Fermentation
  • Degree of Juice Clarification
  • Lees Filtration
  • Rotary Drum Filters