Introduction to Wine

• Wine is an undistilled alcoholic beverage made mainly from fruit juice, especially grapes.
• Vinification is the process of wine preparation.
• Enology (American) or oenology (British) is the study of wine.
• Wine can be made from fruits, berries, and non-toxic plants like flowers.
• Wine contains 3-22% alcohol, along with other substrates.

Wine Types Based on Characteristics

• Color: Red wines are pigmented, while white wines are not.
• Sugar Content: Sweet wines retain some sugars post-fermentation, while dry wines have all sugars fermented into alcohol.
• Alcohol Content:
  • Table wine has 3-10% alcohol.
  • Fortified wine has 19-22% alcohol, is made by adding whisky because yeast cannot accumulate more alcohol.
  • Dessert wine is also a fortified sweet wine and has 22% alcohol.
• Carbonation:
  • Still wine has no CO2 produced during fermentation.
  • Sparkling wine has CO2 produced during fermentation, for example, champagne.

Microbiology

• Grape juice (27% sugar) is fermented by Saccharomyces cerevisiae strains.

Wine Production Overview

• Wine is made by transforming sugars from grapes with yeast in anaerobic conditions into ethanol, CO2, and small amounts of byproducts like D-glucose.

Winemaking Steps

• Harvesting: Appropriate fruits and berries with high fermentable sugars are harvested; grapes contain 5-25% total soluble sugar.
• Crushing and Extraction: Fruits are crushed and extracted mechanically, releasing juice and pigment; the resulting mass is called Must.
• White wine preparation involves removing the skin and de-steaming the harvested fruits.
• Red wine production uses steam to impart a vegetable aroma from 2 methoxy-3-isopropyl pyrazine; color is also extracted from steam, and the Must should be fermented.
• Optimization: Must is optimized for TSS (17-22%) and pH (3-4), depending on yeast strains.
• KNS (potassium metabisulphite), acts as an antimicrobial against Acetobacter spp. and competitive yeast ,plus acts as an antioxidant and antifungal agent; it may be added.
• Primary Fermentation: Optimized Must is inoculated with 2-10% inoculum and fermented under optimum temperature.
  • Red wine: 22-27°C for 3-5 days.
  • White wine: 10-21°C for 7-14 days.
• The mixture is aerated by "punching" the floating skin twice a day, which also aids color extraction.
• The rapid multiplication of yeast cells and sugar fermentation to ethanol occurs during fermentation, terminating when TSS decreases to 9-10%.
• Pressing: The skin of must is removed and pressed to obtain juice and alcohol, and the liquid is transferred into a tank for white wine pressing occurs before fermentation.
• Color extraction of fruits and berries happens during pressing.

Stabilization

• Heat and Cold Sterilization: This removes the tartrate crystals (wine diamonds or crystals).
  • Cold Sterilization: Fermented must is cooled to nearly freezing for 1-2 weeks. Crystals separate on the fermenter wall, and clear liquid is collected in a secondary tank.
• Heat Stabilization: Gently heated between 50-60°C for an hour and the mixture kept overnight to decant proteins. Clear contents are pumped out, and turbid substances are adsorbed onto bentonite.

Secondary Fermentation

• Done in stainless steel, oak barrel, or plastic-lined concrete tank.
• Stabilized, sterilized wine is kept at 15-20°C for 3-6 months under strict anaerobic conditions, usually terminated when sugar content reaches 4-6% for sweet wine.
• During this stage, aroma develops.

Aroma Categorization

• Primary aroma comes from fruits or berries.
• Secondary aroma develops during secondary fermentation.
• Tertiary aroma develops during bottled aging.
• The aroma compound can be volatile or non-volatile.
• Aroma develops through chemical reactions among acids (malic, citric), sugars, alcohols, and phenolic compounds.
• Key aroma contributors include methoxyparazine, monoterpenes, nor-isoprenoids, thiols, and esters (principal).
• Esters are slowly produced by the reaction between alcohols and acids, over nearly a year.
• Before secondary fermentation, malo-lactic fermentation occurs where malic acid converts to lactic acid via lactic acid bacteria (LAB).

Testing, Blending, Fining, Preservation and Bottling

• Laboratory Testing: Conducted after secondary fermentation, including bricks reading, bricks pH, titrable acidity, residual sugars, free or available sulfur, total sulfur, volatile acidity, and alcohol percentage.
• Blending and Fining: Critical for wine quality, taste, and aroma, spices, aromatic plant extracts, essential oils, and fruit juices are added in blending, a process kept secret in the wine industry.
• Fining: Tannins and microscopic particles are removed for clarity treated with gelatin, potassium caseinate, egg albumin, lysozymes, or skimmed milk powder, then filtered, and pectinase enzyme is used.
• Preservation: Pasteurization and KMS (Potassium metabisulphite) are used to inhibit sugar-utilizing microorganisms.
• Bottling: Wine is aseptically filled into bottles corked with oak; the outside cork is sealed, and the bottled wine is ready for consumption or preservation.