1/9/2017
Ester Taints Wine Flavor 101 January 2017
Linda F. Bisson Department of Viticulture and Enology University of California, Davis, CA
Outline of Presentation
Introduction to Esters Ester Formation during Fermentation Stability of Esters
1 1/9/2017
Introduction to Esters
What Is an Ester?
Volatile molecule Formed chemically from the reaction of an alcohol and a keto acid (slow in wine conditions) Formed enzymatically from an alcohol and a keto acid bound to the cofactor, Coenzyme A (fast in wine conditions) Characteristic fruity and floral aromas that become more negative as concentration increases
2 1/9/2017
Ester Formation
O
R1-OH + R2-CCoA
O
R1-O-C-R2
Where do Esters Come From?
Can be formed by the chemical reaction of an alcohol and a keto acid Can be formed enzymatically by the plant Can be formed enzymatically by microbes
3 1/9/2017
Where do Esters Come from in Wine?
Can be formed by the chemical reaction of an alcohol and a keto acid Can be formed enzymatically by the plant Formed enzymatically by microbes – Non-Saccharomyces yeasts – Saccharomyces – Lactic acid bacteria – Acetic acid bacteria
The Two Ester Classes:
Ethyl esters of acids – Keto acids from amino acid catabolism – Fatty acids from fatty acid biosynthesis or lipid degradation – Reaction with ethanol Acetate esters of alcohols – Ethanol – Derivatives from nitrogen metabolism » Fusel oils from amino acid catabolism » Alcohols from purine and pyrimidine catabolism – Reaction with acetyl-CoA
4 1/9/2017
Common Esters Found in Wine
Ethyl Acetate (most 2-Methylpropyl Acetate common) 2-Methylbutyl Acetate Ethyl Propanoate 3-Methylbutyl Acetate Ethyl -2-Methylpropanoate (Isoamyl acetate) Ethyl-2 -Methylbutanoate Hexyl Acetate Ethyl-3-Methylbutanoate – Requires grape precursor Isobutyl Acetate Ethyl Lactate – Bacterial in origin
Issues with Ester Formation
Low concentrations are positive: – Fruit characters (tropical, apple) – Generic fruit (enhances perceptions of varietal fruit characters) – Floral characters (rose, violet) High concentrations are negative: – Too dominating of profile (strong yeast signature) – Mask other characters (depress ability to sense them) – Are definitely microbial and not varietal It is important to know the progression of aroma traits as a function of concentration
5 1/9/2017
Positive Wine Characters Associated with Esters
Fruit Tropical fruit – Apple – Banana – Apricot – Coconut –Fig – Mango – Melon – Pineapple – Peach Floral – Pear –Rose – Prune Butter – Raspberry – Strawberry Spice – vanilla Honey Yeast (bread)
Esters Associated with Apple
Amyl acetate Ethyl acetate Ethyl butyrate Isobutyl acetate Phenethyl acetate
6 1/9/2017
Esters Associated with Pineapple
Ethyl acetate Ethyl butanoate (Ethyl butyrate) Ethyl hexanoate
Esters Found in Chardonnay
Concentration Range Across Ester Strains (mg/L) Ethyl Acetate 50 - 95 Ethyl Butyrate 0.4 - 0.75 Isoamyl Acetate 3.5 - 11.0 Hexyl Acetate 1.0 - 1.7 Ethyl Hexanoate 1.0 - 2.2 Ethyl Octanoate 1.4 - 2.0 Ethyl Decanoate 0.6 - 0.9
7 1/9/2017
Negative Wine Characteristics Associated with Esters
Foxy Nail polish Bubble gum/cotton candy Soapy Candle wax Perfume Intense fruit Intense floral Combinations with other compounds can be quite negative: two positives can create a negative
Ester Expression
Dependent upon chemical species present Dependent upon concentrations: relative and absolute Dependent upon matrix factors Dependent upon yeast strain and substrates
8 1/9/2017
In General . . .
The higher the concentration the more negative the impression is of the character Longer chain esters fall into soapy, perfume range Combinations of esters can confer a stronger aroma than the sum of the individual compounds
Negative Ester Characters
Nail polish/glue: ethyl acetate Soap: ethyl octanoate, ethyl decanoate Perfume: hexyl acetate Rose: phenethylacetate, phenethyl alcohol Apple/unripe apple: Ethyl 2-methyl- butyrate
9 1/9/2017
Esters Found in Chardonnay
Concentration Range Across Ester Strains (mg/L) Ethyl Acetate 50 - 95 Ethyl Butyrate 0.4 - 0.75 Isoamyl Acetate 3.5 - 11.0 Hexyl Acetate 1.0 - 1.7 Ethyl Hexanoate 1.0 - 2.2 Ethyl Octanoate 1.4 - 2.0 Ethyl Decanoate 0.6 - 0.9
Ester Formation During Fermentation
10 1/9/2017
Ester Formation during Fermentation
Influence of non-Saccharomyces yeasts Production by Saccharomyces Production by acetic and lactic acid bacteria
Production by Non-Saccharomyces yeast
Grape flora Winery residents Primary genera: – Hanseniaspora (Kloeckera) – Metschnikowia (Candida) – Candida – Pichia – Torulaspora – Kluveromyces
11 1/9/2017
Production by Non-Saccharomyces yeast
Contribute generic fruity and floral notes Can make excessive ethyl acetate (Hanseniaspora) Better adapted to lower temperatures than Saccharomyces – Bloom during cold-settling – Bloom during cold maceration – Can be sulfite tolerant
Production by Saccharomyces
Yeast Strain Nutrition (Sugar, Nitrogen) – Generally increased nitrogen in vineyard increases ester concentrations – During fermentation impacted by both nitrogen + source (NH4 , amino acids) and nitrogen level interacting with yeast genetic background Temperature Grape Variety
12 1/9/2017
Stability of Esters
Ester Loss Volatilization: – temperature dependent – fermentation vigor dependent Hydrolysis: – pH dependent – time dependent Matrix effects: – masking: ethanol – enhancing: sugar, polyphenol, tannin
13 1/9/2017
Ester Taint Tasting
Glass 1: Control Chardonnay wine Glass 2: Phenethyl alcohol: rose/floral/perfume Glass 3: Phenethylacetate: honey/rose Glass 4: Ethyl butyrate: tropical Glass 5: Ethyl 5-methyl butyrate: green apple Glass 6: Ethyl octanoate: tropical/sour apple/soap
Ester Tasting
Compound conc. in wine threshold in glass (mg/L) (mg/L) (ppm)
Phenethyl ethanol 18-197 10 100.0 Phenethyl acetate trace-0.75 0.25 1.0 Ethyl butyrate 0.7-2 var 1.5 Ethyl 2-methyl butyrate trace-0.03 var 0.03 Ethyl octanoate 0.05-3.8 0.02 2.0
14