wine

FST3101 Food Fermentation and Microorganisms Lecture Overview

Lecture Details

  • Course: FST3101 Food Fermentation and Microorganisms

  • Lecture Title: Wine Science

  • Instructor: Dr. CHUA Jian Yong

  • Affiliation: Department of Food Science & Technology, NUS

  • Email: jianyong.chua@nus.edu.sg

Philosophy of Wine

  • Quote: "A bottle of wine contains more philosophy than all the books in the world." - Louis Pasteur

Introduction to Oenology

  • Oenology:

    • The science of (grape) wine, including the principles of winemaking and vinification.

  • Roles:

    • Oenologist: Wine scientist focused on the scientific aspects of winemaking.

    • Winemaker: Wine technologist who handles practical aspects of winemaking.

  • Key Players in Winemaking:

    • Yeasts, particularly Saccharomyces, which are crucial for fermentation.

    • Sometimes, non-Saccharomyces yeasts may be involved but are not the primary agents.

Definition of Wine

  • Wine: Product of alcoholic fermentation of grape juice or grape must, which can be exclusively grape juice or include skins and seeds.

  • Alternatives: Other fruit wines such as apple, pear, pineapple, and honey wine (mead) that utilize similar winemaking techniques.

Wine Classification by Sugar Content

  • Types of Wine Based on Residual Sugar:

    • Dry Wine: Residual sugar up to 0.4%.

    • Medium-Dry Wine: Residual sugar up to 1.2%.

    • Medium Wine: Residual sugar up to 4.5%.

    • Sweet Wine: Residual sugar over 4.5%, often greater than 10%.

    • Dessert Wine: Very sweet, typically 10-20% sugar, possibly fortified with sugar and/or ethanol (>14% v/v).

Wine Classification by Color

  • Types of Wine Based on Color:

    • Red Wine: Varietals include Pinot Noir, Cabernet Sauvignon, Merlot, Shiraz/Syrah.

    • White Wine: Varietals include Chardonnay, Riesling, Sauvignon Blanc, Pinot Gris.

    • Rosé Wine: Made from red wine grapes with minimal skin contact.

    • Orange Wine: Produced from white grapes but with extended skin contact.

Grape Varieties

  • Common grape varieties include:

    • Cabernet Sauvignon

    • Grüner Veltliner

    • Pinot Noir

    • Riesling

Geographic Relevance of Wine

  • Southeast & East Asia Wine Market:

    • Growing consumer interest in wine.

    • Wine production is challenging in Southeast Asia due to hot climates that are not optimal for grape cultivation (e.g., Vietnam and Thailand).

    • Tropical fruit wines show significant potential; knowledge gained from grape winemaking can be adapted with modifications for fruit wines.

Grape Maturity and Harvesting

  • Indicators for Harvesting Grapes:

    • Sugar Levels: Measured using a refractometer.

    • Acidity: Measured as titratable acidity (TA) and pH.

    • Sugar/Acid Ratio: Important maturity index.

    • Flavor: Assessed through sensory analysis (taste and aroma) and chemical components (terpenes, phenolics, color).

    • Note: Sugar and acid contents can be adjusted, subject to regulations.

Components of Grape Juice

  • Main Substances and Concentrations:

    • Glucose: 75-150 mg/ml

    • Fructose: 75-150 mg/ml

    • Pectin: 0.1-1 mg/ml

    • Tartaric Acid: 2-10 mg/ml

    • Malic Acid: 1-8 mg/ml

    • Citric Acid: 0.1-0.5 mg/ml

    • Amino Acids (Total): 150-2,500 μg/ml

Sugar Composition in Grapes

  • Analysis involving 18 grape cultivars shows a detailed breakdown of major and trace sugar components.

Grape Crushing and Supplementation

  • Supplementation Practices:

    • Acidity and pH Adjustment: Adjustments made based on climate conditions.

    • Sulphur Dioxide: Used to inhibit wild yeasts/bacteria, typically ≤50 mg/L to minimize oxidation.

    • Ascorbic Acid: Amounts of 50-100 mg/L added to reduce oxygen and limit oxidation, particularly in white wine.

    • Nutrients and Enzymes: May be added to enhance juice extraction and flavor profile.

Role of Sulphur Dioxide (SO2)

  • Uses in Wine Production:

    • Inhibitory effects on unwanted microbial growth.

    • Various forms depend on pH, affecting various phases of winemaking.

    • Interaction with water and different compounds yields diverse forms relevant for winemaking efficacy.

Wine Fermentation Process

  • Overview:

    • Red Wine: Fermented with skins and seeds (maceration).

    • White Wine: Fermentation occurs post-crushing after removal of solids.

    • Malolactic Fermentation: Induced based on grape composition and desired wine style.

Carbonic Maceration

  • Methodology: Developed in 1934, involves intact grapes in a sealed vessel with pumped CO2, leading to internal fermentation.

Microbial Involvement in Winemaking

  • Types of Microbes:

    • Yeasts: Drive alcoholic fermentation and can cause spoilage.

    • Molds: Can negatively impact barrels/tanks; exceptions include wine made from Botrytis cinerea.

    • Lactic Acid Bacteria and Acetic Acid Bacteria: Play roles in malolactic fermentation and spoilage depending on circumstances.

Yeast Starter Cultures for Fermentation

  • Types of Yeast:

    • Natural Yeasts: Offer complex aromas but can lead to unpredictable results.

    • Cultured Yeasts: Promote controlled fermentation, manageable in a winery environment.

    • Active Dried Yeasts (ADY): Convenient commercial options for winemaking.

Comparison: Starter Cultures vs Natural Fermentation

  • Starter Cultures:

    • Cleaner flavor, greater consistency, and less chance of stuck fermentations.

  • Natural Fermentation:

    • More complex flavors but slower and less predictable.

Commercial Wine Yeasts

  • Key Strains:

    • Saccharomyces cerevisiae: Used for table wines.

    • Saccharomyces bayanus: Preferred for sparkling wines.

Desirable Yeast Characteristics

  • Traits include:

    • High ethanol production, unique flavors, rapid fermentation rates, low sensitivity to killer yeasts, genetic stability.

Fermentation Pathways

  • Overview of glucose/fructose conversion during fermentation leading to ethanol and CO2 production.

Ethanol Yield from Sugar Fermentation

  • Theoretical vs Actual Yield: Estimates yield variations based on enzymatic effects and fermentation conditions.

Compounds Produced during Alcoholic Fermentation

  • Common Compounds:

    • Ethanol, Propanol, Isobutanol, Isomers, acetic acid, etc., each contributing distinct flavor profiles.

Biological Stability in Wine

  • Post-Malolactic Fermentation Considerations: Treating wines afterward to achieve stability against microbial growth and spoilage.

Wine Spoilage Microbes

  • Impact of Various Microbes:

    • Acetic acid bacteria, lactic acid bacteria, and spoilage yeasts contribute to undesirable properties in wine.

Post Fermentation Management

  • Practices:

    • Aging in oak barrels for flavor development, clarification through racking or fining agents, and blending to enhance complexity.

Wine Aging Effects

  • Examine how aging changes the chemical composition of wine, increasing concentration yet decreasing volatile aromas.

Ice Wine Making Processes

  • Traditional vs. Modern: Both methods focus on harvesting frozen grapes early in the morning to extract high sugar and acid juice.

Summary of Wine Fermentation Processes

  • Key Elements:

    • Alcoholic and malolactic fermentation involving Saccharomyces yeasts and Oenococcus oeni, with various spoilage risks from other microbes.