Wine Fermentations

White Wine

• Uses clarified juice (solids and liquids)

• Drained, pressed, settle/rack, then yeasts are added

• Barrel ferment (LAB is added) to barrel age

• OR tank ferment

Red Wine

• Use the whole unwashed fruit (stems, skin, seeds, bugs) - flavor and color

• Must (liquid) ferment (no draining/separation) with added yeasts

• Settle/rack (lees is what comes out)

• Barrel age

• Then regular rack, blend, fine, tartrate stabilization, filter, sterile filter, bottle

SO2 is added

• Kills or suppresses other unwanted microbes

  • This helps control microbial populations so that the desired yeast strain (e.g., Saccharomyces cerevisiae) dominates the fermentation

• To prevent oxidation (antioxidant)

• Slow down fermentation

• Aroma protection

Wine fermentations

From Juice to wine…

• Carbs decrease

• Nitrogenous compounds decrease (from a.a. and ammonia, fermentations will stop from running out of oxygen)

• Ethanol increases

Microbial Ecology of Wine Fermentations

• Yeast biomass is grown first

• Ethanol increases

• Sugar decreases

Ecology of Wine Fermentations

• AAB and molds are aerobic but persist in anaerobic conditions

• Yeasts

• LAB are considered spoilage microbes

In lower pHs…

• Lactobacillus, Lactococcus, Pedicoccus, Leuconostoc, Oenococcus increased at the beginning and decrease as sugar is eaten

• Oenococcus seen as sugar decrease, ethanol INCREASES

In higher pHs…

• Lactobacillus, Lactococcus, Pedicoccus, Leuconostoc, and Oenococcus decrease as sugar is consumed

• Lactobacillus, Pedicoccus, Oenococcus are seen as ethanol increased

Microbial Terroir

Microbe makeup will be different based on the region its made in

Saccharomyces cerevisiae

Glucophilic - prefers glucose over fructose (or other)

Yeast Fermentative Metabolism

• Uses facilitated diffusion: doesn’t use ATP, works as a “revolving door”

Hexose Transporters - Wine Ferm.

• 7 main players

  • Hexose transporter 1 induced in high [glucose] at start of ferm (low glucose affinity) - worse vacuum cleaner

• Other 11, main purpose for signaling but also transports

• Uses facilitated diffusion

Wine Fermentations - Yeast Nitrogen

A.A., ammonia, nucleotides (DNA), peptides (larger a.a.) are sources of nitrogen in grape juice/wine

Depending on the N-compound - it can be utilized via:

• Incorporated into cell metabolism w/o modification (i.e. a.a. taken up and used in protein synthesis)

• As a source of nitrogen - cell takes up N-compound and degrades it to get at N, may use or excrete C remaining

• As a source of C - cell takes up N-compound and degrades it to get at C, may use or excrete N remaining

Majority of N-compounds used as sole source of N

EXCEPT (because it already has these):

• Lysine (K), cysteine (C), proline (P), and to a lesser extent histidine (H), and glycine (G)

• Large peptides and proteins

  • Saccharomyces cerevisiae can’t degrade (no extracellular proteases) but other yeast might

Malolactic Fermentation

Effects on wine (not microbe)

• Deacidification (convet to survive in acid longer)

• Microbial stabilization

• Flavor effects (lactic acid is softer on the palate, diacetyl can be made)

• Other endproducts

Oenococcus oeni - “Malolactic” (ML) Starter Cultures

Used as starter culture to induce the malolactic fermentation in wine

• Kunkee

• Can survive low pH (high alcohol)

Why malate is converted to lactate

No middle steps where carbon is used

• CO2 produce, lactate endproduct

• Reduces acidity

• Prevents spoilage

• No significant benefit from pH

Malate conversion generates proton motif force (PMF)

Conversion to malate to lactate consumes a proton so you don’t have to use ATP to push that proton out of the cell (saves energy) - lowers pH

Diacetyl influences in wine

• Strain

• Oxygen concentration (aeration)

• Redox potential of the wine

• Citrate concentration

• SO2

  • Impact on LAB growth/metabolism

  • Direct rxn w diacetyl (and is reversible over time)

Not all ML conversions are friendly…

Can make taints…

• Volatile acidity (acetate production)

• Mousiness (mouse urine smell)

• Acrolein taint (bitter taste)

• Mannitol taint (coincides w acetate)

• Ropiness (exopolysaccharide)

• Biogenic amines (amino acid decarboxylation)

Mannitol taint in hetero. LAB

Fructose —> Mannitol, generation of NAD+

• Mannitol crystal test for hetero. pathway ID

Wine Fermentation Spoilage

Vinyl Phenols

1. Source: decarboxylation & reduction of phenols - off-character, phenolic, animal

2. Organisms involved

   • Brettanomyces/Dekkera (major prducers)

   • LABs (first step)

Volatile Phenols

Brettanomyces is main culprit responsible for volatile phenols

Some LAB

4-ethyl phenol results in the descriptors

• “poorly cured leather”

• “horse sweat”

• “used socks”

• “horse stable”

Cork taint - Tricloroanisole (TCA)

• Musty taint

• Organisms responsible: molds, bacteria

• Where are they: corks, cardboard, wood in winery (pallets etc.), drains,

• Why do they make it?

  • Detoxification (methylation seems a response to detoxify it)

• Cork taint rate 1-8%

• Est. cost $100-800 M/yr