Fermentation Process and Effects of Alcohol

Fermentation Process

• The major reaction: C6H12O6 → 2 CH3CH2OH + 2 CO2
• Beneficial effects of moderate alcohol consumption:
  • Feeling relaxed
  • Stimulation of senses and appetite
  • Heightening of pleasure
  • Providing sense of euphoria (intensive feeling of well-being)
• Negative effects of excessive alcohol consumption:
  • Impairs mobility
  • Impairs muscular coordination
  • Impairs eyesight
  • Delays reaction time
  • Induces serious diseases (Cirrhosis, Liver cancer, Gallstone, Kidney stone)

Blood Alcohol Concentration (BAC) Effects

• 0.02%: Relaxed, slow reaction time
• 0.04%: Vision affected
• 0.08%: Coordination decreased, impaired driving skills (legal drinking limit in the US)
• 0.10%: Slurred speech, lost coordination and judgment
• 0.15%: Stumbling, trouble standing up
• 0.30%: Vomiting, likely to pass out
• 0.40%: Passing out, coma (unconsciousness lasting more than six hours)

Unwanted Fermentation

• Glycerol fermentation: lactic acid + acetic acid
• Natural grape sugars fermentation: lactic acid + acetic acid
• Tartaric acid fermentation: lactic acid + acetic acid + CO2
• Ethanol fermentation: Acetic acid → water + CO2, reducing wine quality

Odorous Byproducts of Fermentation

• Acetic acid: sour, vinegary
• Acetone: nail varnish
• Acetoin: buttery, creamy
• Aldehydes (various): buttery, fruity, nutty
• Butyric acid: rancid butter
• Diacetyl: buttery, cloying
• Diethyl sulfide: ether, pungent
• Ethanal (acetaldehyde): Sherry-like, oxidized, unpleasant
• Esters (various): fruity, floral
• Formic acid: tart, pungent
• Fumaric acid: smoky, pungent
• Glycerol: mouthfeel, sweetness
• Higher alcohols (various): pleasant floral → sickly fusel aromas
• Hydrogen sulfide: rotten egg

Fermented Drinks Categories

• Alcohols: liquors, spirits
• Wines
• Beers
• Kombucha (Thủy hoài sâm)
• Nata de coco drink
• Straw liquor (Rượu cần)

Fermentation Process in Straw Wine Production

• Rice cooking and mixing with rice husk
• Yeast cake powder supplementation
• Biomass growth → aerobic fermentation → anaerobic fermentation in big-bellied jar
• Alcohol production → yeast cake for straw wine of K’HO minority

Kombucha (Thủy hoài sâm) Fermentation

• Mixture of sugar (7-10%) and tea fermented by yeast and acetic bacteria
• Two fermentation processes: alcoholic (yeast) and vinegar (acetic bacteria)
• Fermentation process divided into primary (alcoholic) and secondary (malo-lactic) fermentations

Fermentation Process in Winemaking

• Primary fermentation: 10-12 days at 20-22°C, 6-7 days at 25-28°C
• Pure culture can be added at this stage
• Role: produce alcohol, reaching 8-10% or more
• Equation: C6H12O6 + 2Pi + 2ADP + 2H+ → 2C2H5OH + 2CO2 + 2ATP

Wine Production

• Wine is not pure due to ease of infection and presence of many by-products
• Wine becomes sour due to accumulation of organic acids
• To overcome this problem, pure yeast Saccharomyces cerevisiae is used
• Saccharomyces cerevisiae has advantages, including rapid and complete fermentation, well-settling, and creation of a distinct aroma for wine

Yeast in Wine Production

• Saccharomyces cerevisiae is commonly used to ferment grape juice to wine
• Yeast is present on the outside of grapes

Wine Definition and Classification

• Wine is a fermented beverage from grapes or other fruits
• Wine is a non-distillation alcoholic drink with ethanol concentration normally in the range of 7 - 15%
• Wine classification is based on color, sweetness, fermentation, CO2 level, and producer
• Wine types include:
  • White wine (white/pale color): made from juice of white/green-skin grapes
  • Rosé wine: made from red/purple grapes with maceration for a few hours
  • Red wine (red/purple/opaque color): made from mixture of grape juice, skins, and seeds of dark-skin grapes
• Sweetness levels:
  • Dry wine: all sugar is converted to alcohol
  • Semi-dry (off-dry) wine: has a mild or softly perceptible sweetness
  • Sweet wine (dessert wine): still has some residual sugar due to short fermentation time or using low-alcoholic producing yeast

Grape Variety and Ripeness Criteria

• Grape variety affects wine quality and type
• Ripeness criteria for different wine types include:
  • Sugar concentration (°Brix)
  • Titratable acidity (g/l)
  • pH
• Typical values for ripeness criteria vary by wine type

Chemical Composition of Grape and Wine

• Microorganisms in wine production include Saccharomyces cerevisiae and Lactobacillus hilgardii
• Unwanted fermentation can produce acetic acid, glycerol, and other by-products that affect wine quality
• Fermentation by-products can have characteristic odors, such as sour, vinegary, or fruity

Racking and Malolactic Fermentation

• Racking is the process of transferring wine to remove settled matters and prevent tannin extraction
• Malolactic fermentation is a process where tart-tasting malic acid is converted to softer-tasting lactic acid by lactic acid bacteria
• Malolactic fermentation occurs after alcoholic fermentation and is traditionally done during wine ageing and maturation

Fermentation Process

• Divided into 2 main phases: Primary fermentation (alcoholic fermentation) and Secondary fermentation (malolactic fermentation)
• Can be fermented in open or closed fermenters
• Opened fermentation tanks are more easily operable and temperature-controllable
• Closed tanks are more popular for ensuring sanitary conditions
• Fermentation in small amounts can be done in vases, boxes, plastic or stainless steel containers

Primary Fermentation

• Optimum temperature for dry white and rose wine: 15-28°C
• Optimum temperature for red wine: 25-30°C
• Lasts for 10-12 days at 20-22°C, 6-7 days at 25-28°C
• Pure culture can be added at this stage
• The main role is to produce alcohol
• When completed, alcohol content reaches 8-10% or more
• Equation for glucose metabolism to ethanol: C6H12O6 + 2Pi + 2ADP + 2H+ → 2C2H5OH + 2CO2 + 2ATP

Crude Wine Pressing

• Purpose is to eliminate skins from the fermented juice
• Juice is drawn out, and the remained pulp is continually pressed
• Fermented juice is then transferred to tanks for secondary fermentation (malolactic fermentation)

Malolactic Fermentation

• Process where tart-tasting malic acid is converted to softer-tasting lactic acid by lactic acid bacteria
• Normally occurs after alcoholic fermentation and frequently happens automatically when wines are stored in barrels for ageing and maturation

MLF Bacteria Characteristics

• Oenococcus oeni: Spherical/lens-shaped cocci, occur in pairs and chains, heterolactic fermentation
• Leuconostoc: Spherical/lens-shaped cocci, occur in pairs and chains, heterolactic fermentation
• Lactobacillus: Long, slender rods, sometimes bent, heterolactic and homolactic fermentation
• Pediococcus: Spherical cocci, occur in tetrads, homolactic fermentation

Categories of Fermented Drinks

• Alcohols: liquors, spirits
• Wines
• Beers
• Kombucha (Thủy hoài sâm)
• Nata de coco drink
• Straw liquor (Rượu cần)

Distilled Drinks

• Spirits: distilled from fermented rice, sticky rice, cassava, corn…
• Whisky: distilled from fermented grain mash (corn, barley, wheat…)
• Rhum: distilled from fermented molasses
• Cognac: distilled from must (fermented grape)

Unwanted Fermentation

• Glycerol fermentation → lactic acid + acetic acid
• Natural grape sugars → lactic acid + acetic acid
• Tartaric acid → lactic acid + acetic acid + CO2
• Ethanol → Acetic acid → water + CO2
• Reduces wine quality
• Requires frequent smell and taste checks to ensure proper primary and secondary fermentations

Odorous Byproducts of Fermentation

• Acetic acid: sour, vinegary
• Acetone: nail varnish
• Acetoin: buttery, creamy
• Aldehydes (various): buttery, fruity, nutty
• Butyric acid: rancid butter
• Diacetyl: buttery, cloying
• Diethyl sulfide: ether, pungent
• Ethanal (acetaldehyde): sherry-like, oxidized, unpleasant
• Esters (various): fruity, floral
• Formic acid: tart, pungent
• Fumaric acid: smoky, pungent
• Glycerol: mouthfeel, sweetness
• Higher alcohols (various): pleasant floral → sickly fusel aromas
• Hydrogen sulfide: rotten egg