Linda F. Bisson
Department of Viticulture and Enology
University of California, Davis, CA

 Introduction to Esters
 Ester Formation during Fermentation
 Stability of Esters

 Volatile molecule
 Formed from the reaction of an alcohol and a keto acid
 Formed enzymatically from an alcohol and a keto acid bound to the cofactor,
Coenzyme A
 Characteristic fruity and floral aromas

O
R
1
-OH + R
2
-C

CoA
O
R
1
-O-C-R
2

 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

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
 Can be formed enzymatically by microbes
– Non-Saccharomyces yeasts
– Saccharomyces
– Lactic acid bacteria
– Acetic acid bacteria

 Ethyl esters of acids
 Acetate esters of alcohols

 Ethyl esters of acids
– Keto acids from amino acid catabolism
– Fatty acids from fatty acid biosynthesis or lipid degradation
 Acetate esters of alcohols
– Ethanol
– Derivatives from nitrogen metabolism
» Fusel oils from amino acid catabolism
» Alcohols from purine and pyrimidine catabolism

 Ethyl Propanoate
 Ethyl -2-Methylpropanoate
 Ethyl-2 -Methylbutanoate
 Ethyl-3-Methylbutanoate
 Isobutyl Acetate
 2-Methylpropyl Acetate
 2-Methylbutyl Acetate
 3-Methylbutyl Acetate
(Isoamyl acetate)
 Hexyl Acetate
– Requires grape precursor
 Ethyl Lactate
– Bacterial in origin

Positive Wine Characters
Associated with Esters
 Fruit
– Apple
– Apricot
– Fig
– Melon
– Peach
– Pear
– Prune
– Raspberry
– Strawberry
 Honey
 Tropical fruit
– Banana
– Coconut
– Mango
– Pineapple
 Floral
– Rose
 Butter
 Spice
– vanilla
 Yeast (bread)

 Amyl acetate
 Ethyl acetate
 Ethyl butyrate
 Isobutyl acetate
 Phenethyl acetate

Esters Associated with Pineapple
 Ethyl acetate
 Ethyl butanoate (Ethyl butyrate)
 Ethyl hexanoate

Ester
 Ethyl Acetate
 Ethyl Butyrate
 Isoamyl Acetate
 Hexyl Acetate
 Ethyl Hexanoate
 Ethyl Octanoate
 Ethyl Decanoate
Concentration Range Across
Strains (mg/L)
 50 - 95
 0.4 - 0.75
 3.5 - 11.0
 1.0 - 1.7
 1.0 - 2.2
 1.4 - 2.0
 0.6 - 0.9

Negative Wine Characteristics
Associated with Esters
 Foxy
 Nail polish
 Bubble gum/cotton candy
 Soapy
 Candle wax
 Perfume
 Intense fruit
 Intense floral

 Dependent upon chemical species present
 Dependent upon concentrations: relative and absolute
 Dependent upon matrix factors
 Dependent upon yeast strain and substrates

 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

 Nail polish/glue: ethyl acetate
 Soap: ethyl octanoate, ethyl decanoate
 Perfume: hexyl acetate
 Rose: phenethylacetate, phenethyl alcohol

Ester
 Ethyl Acetate
 Ethyl Butyrate
 Isoamyl Acetate
 Hexyl Acetate
 Ethyl Hexanoate
 Ethyl Octanoate
 Ethyl Decanoate
Concentration Range Across
Strains (mg/L)
 50 - 95
 0.4 - 0.75
 3.5 - 11.0
 1.0 - 1.7
 1.0 - 2.2
 1.4 - 2.0
 0.6 - 0.9

Ester Formation During Fermentation

Ester Formation during
Fermentation
 Influence of non-Saccharomyces yeasts
 Production by Saccharomyces

Production by Non-Saccharomyces yeast
 Grape flora
 Winery residents
 Primary genera:
– Hanseniaspora (Kloeckera)
– Metschnikowia (Candida)
– Candida
– Pichia
– Torulaspora
– Kluveromyces

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

 Yeast Strain
 Nutrition (Sugar, Nitrogen)
–
–
Generally increased nitrogen in vineyard increases ester concentrations
During fermentation impacted by both nitrogen source (NH
4
+ , amino acids) and nitrogen level interacting with yeast genetic background
 Temperature
 Grape Variety

Ester Formation in Wines
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
ISOAMYL ACETAT E
100 200 300 400
Time (Hours)
500 600
5.1
5.08
5.06
5.04
5.02
5
700
4.98
Vianna & Ebeler, 2001 J. Agric. Food Chem., 49(2): 589-595

 Volatilization:
– temperature dependent
– fermentation vigor dependent
 Hydrolysis:
– pH dependent
– time dependent
 Matrix effects:
– masking: ethanol
– enhancing: sugar, polyphenol, tannin

 Generally lost upon aging in barrel
(volatilization and hydrolysis)
 Lost upon aging in bottle (hydrolysis)
 Most esters gone six months postfermentation, depending upon aging and temperature of aging

 Management of strains and microbial populations
 Age under conditions favoring loss (or retention)

 Glass 1: Control Chardonnay wine
 Glass 2: Ethyl acetate
 Glass 3: Ethyl octanoate, ethyl decanoate
 Glass 4: Hexyl acetate
 Glass 5: Phenethylacetate, phenethyl alcohol

Glass 6: Rhône 4600 esters, Grenache blanc

 Glass 1: Control Chardonnay wine
 Glass 2: Ethyl acetate: nail polish remover
 Glass 3: Ethyl octanoate, ethyl decanoate: soap
 Glass 4: Hexyl acetate: perfume
 Glass 5: Phenethylacetate, phenethyl alcohol: rose

Glass 6: Rhône 4600 esters, Grenache blanc


Isolated from the Côtes du Rhône region
 Complex aroma notes and elevated ester production such as tropical (pineapple) and fresh fruit (apple, pear, strawberry)