Wine Fermentation
(book excerpts)The process of fermentation in winemaking turns grape musts (unfermented juice of grapes extracted by crushing or pressing) into wine. During fermentation, the yeast consumes the natural grape sugars, producing alcohol and carbon dioxide along with other by-products such as fatty acids, esters, and higher alcohols that contribute to the sensory characteristics of the wine. Although Saccharomyces cerevisiae is generally considered more desirable for efficient alcoholic fermentation, it is possible that other yeast genera may contribute to flavor, especially in the early stages of fermentation. Saccharomyces is preferred because of its efficiency in converting sugar to alcohol and because it is less sensitive to the inhibiting effect of alcohol. The process of alcoholic fermentation requires careful control for the production of high-quality wines. Requirements include suppression of the growth of undesirable microorganisms, presence of adequate numbers of desirable yeasts, proper nutrition for yeast growth, temperature control for prevention of excessive heat, control of oxidation, and proper management of the cap of skins floating in red musts. Fermentation may be done in closed stainless-steel tanks, which is common with many white wines like Riesling, in open tanks, and inside wine barrels.
Click on the following topics for more information on primary alcohol fermentation.
Topics Within This Chapter:
- Wine Fermentors
- Types of Fermentors
- Fermentor Tank Capacity
- Managing Oxygen in Wine Fermentation
- Timing of Oxygen Additions
- Oxygen's Influence on Wine Style
- Post-Fermentation
- Wine Fermentation Temperatures
- Red and White Wines
- Temperature Extremes
- Managing Fermentation Temperature
- Tanks
- Cellar
- Nutrient Management during Wine Fermentation
- What Forms of Nitrogen Can Yeast Use
- Determining the Nitrogen Content
- Methods for Measuring YAN
- YAN Application Rates
- Recommended Rates
- Insufficient Ammonia Levels
- Excessive Ammonia Levels
- Timing of Nutrient Additions
- Commercial Wine Yeast Nutrients
- Diammonium Phosphate
- Complex Nutrients
- Rehydration Nutrients
- Rehydration Protectants
- Yeast Hulls
- Glutathione Enriched Inactivated Yeast
- Pure Vitamin Mixes
- Cap Management for Red Wines
- Punch-Down
- Manual Punch-Downs
- Mechanical Punch-Downs
- Pump-Over
- Manual Pump-Over
- Automatic Pump-Over
- Number of Pump-Overs
- Pumps
- Submerged Cap
- Rack-and-Return
- Pulsair System
- Rotary Fermentors
- Barrel Fermented Wine
- Barrel Fermentation of Red Wines
- Advantages and Disadvantages
- Whole-Cluster Fermentation for Red Wines
- Sensory Effects
- Grape Varieties
- Harvest
- Whole-Cluster Fermentation Techniques
- Carbonic Maceration for Red Wines
- Advantages and Disadvantages
- Sensory Effects
- Phenolic Compounds
- Winemaking Process
- Harvesting
- Filling Tanks with Intact Clusters
- Maceration
- Pressing
- Alcoholic Fermentation
- Wine Fermentation Monitoring
- Digital Refractometer
- Hydrometer
- Density Meter
- Chemical Analysis
- Rebelein Titration
- Enzymatic Analysis
- High Performance Liquid Chromatography
- Plotting the Fermentation
- Predicting Potential Alcohol Levels
- Brix
- Chemical Analysis
- Sampling
- Fermentation Times
- Red Wines
- White Wines
- Stopping the Fermentation
- Chilling
- Yeast Removal
- Racking Wine after Fermentationg
- Racking Operations
- Blending
- Adjusting Sulfur Dioxide Levels
- Aeration of Wine
- White Wine
- Red Wine
- Malolactic Fermentation
- Post-Fermentation Management for Red Wines
- Extended Post-Fermentation Maceration
- Length of Maceration
- Management Practices
- Pressing
- Composition of Press Wines
- Settling Tanks
- Blending Press Wines
- Devatting
- Problem Wine Fermentations
- Sluggish or Stuck Fermentations
- Causes of Sluggish or Stuck Fermentations
- Strategies for Restarting Sluggish or Stuck Fermentations
- Production of Off-Flavors and Off-Aromas
- Sulfur-Containing Volatiles
- Esters
