Lecture 15: Post-Fermentation Cellar Operations: Wine Stability

Reading Assignment: Text, Chapter 9, pages ;

The 5 Goals of Post-Fermentation Operations: 3. STABILITY

Stability GOAL: to stabilize the clarity and desirable sensory characteristics

Stability: Types of Problems Microbial stability Chemical stability Macromolecular stability

Microbial Stability GOAL: to prevent microbial growth and/or metabolism especially in the bottle to prevent both turbidity and off- character production

Spoilage Organisms Bacteria Yeasts Molds

Bacteria Lactic acid bacteria Acetic acid bacteria Bacillus Streptomyces

Lactic Acid Bacteria Off-character production –Mousiness –Acetic acid Turbidity Effervescence (CO 2 ) Polysaccharide –Haze –Ropiness

Mousiness Several compounds(oxidation products of lysine) have been implicated in this off- character: 2,4,6-trimethyl-1,3,5-triazine 2-ethyl-3,4,5,6-tetrahydropyridine 2-acetyl-3,4,5,6-tetrahydropyridine

PREVENTION: Use of SO 2 pH adjustment Control of ML

Bacteria Lactic acid bacteria Acetic acid bacteria Bacillus Streptomyces

Acetic Acid Bacteria Acetobacter aceti Require O 2 Acetic acid accompanied by ethyl acetate

PREVENTION: Use of SO 2 Topping off to prevent O 2 exposure Market it as wine vinegar

Bacteria Lactic acid bacteria Acetic acid bacteria Bacillus Streptomyces

Bacillus Turbidity No off-character production Produces resistant spores Relatively rare

PREVENTION: Use of SO 2 Limit O 2 exposure

Bacteria Lactic acid bacteria Acetic acid bacteria Bacillus Streptomyces

Contaminant of winery filtration equipment Imparts a “soil” character Rare

PREVENTION: Clean equipment after each use!

Spoilage Organisms Bacteria Yeasts Molds

Spoilage Yeasts Zygosaccharomyces

Turbidity Little to no off-characters Resistant to potassium sorbate Most common in semi-dry wines Predominant in juice concentrate More resistant to SO 2

Spoilage Yeasts Zygosaccharomyces Pichia

Can produce turbidity Can produce off-characters Sensitive to SO 2 Sensitive to dimethyldicarbonate (DMDC, “Velcorin”)

Spoilage Yeasts Zygosaccharomyces Pichia Candida

Some strains can produce off- characters Can form a film “C. mycoderma” –Oxidizes acids reducing acidity –Forms acetaldehyde “ethanal” (apple) More common in barrel fermentations/aging Sensitive to SO 2 and DMDC

Spoilage Yeasts Zygosaccharomyces Pichia Candida Brettanomyces/Dekkera

Multiple off-characters –Vinyl phenols –Amino acid degradation products –Oxidation of wood aldehydes More common in barrel aging More common in red wines

The Brett Off-Characters Horsy, horse blanket Barnyard, fecal Wet dog Tar Tobacco Creosote Leathery Pharmaceutical Mousy

Control of Brettanomyces Use of sanitized cooperage Avoid topping off with contaminate wine Filtration of contaminated wine Use of SO 2

Spoilage Yeasts Zygosaccharomyces Pichia Candida Brettanomyces/Dekkera Saccharomyces

Turbidity Effervescence (CO 2 ) More of a problem in wines with high residual sugar Can be prevented by use of SO 2 and sterile bottling

Spoilage Organisms Bacteria Yeasts Molds

Not a problem if wine is protected against O 2 exposure Impart “moldy” taints Can produce “corkiness”: 2,4,6- trichloroanisole

2,4,6 -Trichloroanisole OCH 3 Cl

2,4,6-Trichloroanisole Intense aroma of “moldy rag” Only one of several off-characters that can be associated with bad corks Can be formed in absence of cork if have the right conditions: phenolic compounds, mold and chlorine bleach

Sources of Spoilage Organisms Grapes Winery surfaces/equipment Airborne contaminants Barrels Corks/materials entering winery Blending wines Humans

Prevention of Spoilage Do not allow biologically active waste to accumulate Clean equipment immediately after use, not just before next use Identify source of contamination promptly Minimize outside sources of contamination (know your bulk wine!) Use SO 2 or other anti-microbial Monitor O 2 exposure of wine

Stability: Types of Problems Microbial stability Chemical stability Macromolecular stability

Chemical Instabilities Metal ions

Metal Ions Fe and Cu can form a precipitate “casse” Caused by use of iron or copper containing materials in winery or from pesticides Elimination: Ferrocyanide precipitation (not legal everywhere)

Chemical Instabilities Metal ions Tartrate

At low temperature, tartrate will crystallize Mistaken for ground glass by consumers Unstable in presence of Ca ++ Solubility depends upon pH, K +, tartrate concentrations Can get co-crystallization with other organic acids

Tartrate: The Solution Super-chill wine to catalyze crystallization Nucleate process with tartrate crystals Add cations to initiate crystallization

Chemical Instabilities Metal ions Tartrate Polymerized phenols

Polymerized Phenols Can precipitate during aging Undesired in bottle

Chemical Instabilities Metal ions Tartrate Polymerized phenols Oxidation products

Oxidation Products Off-colors –Brown –Pink –Orange Off-characters –Aldehydes Prevented by using antioxidants

Stability: Types of Problems Microbial stability Chemical stability Macromolecular stability

Macromolecular Stability Protein Polysaccharide

Protein Instability Proteins involved are from grape Denature over time causing visible haze –Hydrophobic regions interact –Agglutination complexes formed –Complex becomes visible Accelerated by treatment of wine at high temperature (HTST) Can be prevented by fining

HTST “High Temperature Short Time” Used on juices with high oxidase levels –Polyphenol oxidase from plant –Laccase from Botrytis Used on wines –Pasteurization (Kosher wines) –Inactivation of added enzymatic activity

Polysaccharide Instability Polysaccharides come from either plant or microbial activity Insoluble at high ethanol causing visible haze Insoluble at low temperatures More difficult to prevent/remove