Impact of Brettanomyces on Wine Quality

Lucy JosephDepartment of Viticulture and Enology

U.C. Davis

Introduction• Brettanomyces is considered to be the

primary spoilage yeast in finished wine

• However, many consumers and critics like the complexity that is derived from Brett growth in wine

Compounds Produced by Brett in Wine

• Signature spoilage compounds - ethyl phenols, vinyl phenols

• Other spoilage compounds – acetic acid, ethyl acetate, fatty acid, carboxylic acid

• Compounds that are positive – Esters, higher alcohols, terpenes

Strain Collection

Alcohol Aldehyde Ester Ethyl Phenol Fatty Acid Terpene Vinyl Phenol

Isoamyl Nonanal Ethyl butanoate

4-ethylphenol Butanoic Ocimene 4-vinylphenol

Amyl (active)

Pentyl formate

4-ethylguaiacol Heptanoic Bisabolene 4-vinylguaiacol

2-ethylhexanol

Ethyl isovalerate

Undecanoic

Phenethyl Ethyl valerate

2-methoxyphenyl

Ethyl 2-methylbutyrate

Octyl-butyrate

Amyl-octanoate

Phenethyl formate

Fruit/floral chemical

Artificial fruit/floral

Artificial fruit/floral

Chemical, smoke/spice

Sweaty/rotten cheese

Floral resin spice

Spicy wood smoke medicinal

Initial Screen• Defined medium was used• Supplemented with amino acids• All strains will make 4EP and 4EG

with coumaric and ferulic acids

Positive and Negative Perception

Selection for Test in Wine

• Descriptors, intensity, and likability used to score strains

• Out of the initial 83 that were successfully screened in the initial screen, 17 were chosen as “positive” and 5 as “negative”

Summary of Aroma for Strains Tested in Wine

SPME-GCMS• These strains were also screened chemically• Used defined medium supplemented with – Aromatic amino acids– Cinnamic acids and aromatic amino acids

• Goal was to identify strains that produced low negative characters

Cluster Analysis of Strains

Important Compounds

That Determine DifferencesWith Amino

Acids

Relative Concentration of Compounds in “Most Liked” Strains – Amino Acid

Supplemented• Phenethyl acetate – Sweet, honey, floral rosy• Ethyl decanoate – sweet, waxy, fruity, apple• Ethyl hexanoate – sweet, fruity, pineapple, waxy

green banana• Ethyl octanoate – fruity, wine, waxy, sweet• 2-phenylethanol – floral, rose, rose water• Octanoic acid – fatty, rancid oil, cheesy• Ethyl acetate – nail polish remover, solvent• 3-methylbutanoic acid – sour, stinky feet, sweaty, cheese • Decanoic acid – rancid, sour, fatty, citrus• 2-phenylacetaldehyde – honey, sweet, rose, green, grassy

Important Compounds

That Determine Differences

With Cinnamic

and Amino Acids

Relative Concentration of Compounds in “Most Liked” Strains – Amino Acid and Phenolic

Acid Supplemented

• Ethyl octanoate – fruity, wine, waxy, sweet• 2-phenylethanol – floral, rose, rose water• Ethyl decanoate – sweet, waxy, fruity, apple• 4-ethylphenol – medicinal, Band-Aid, barnyard• 4-ethylguaiacol – spicy, smoky, phenolic, clove• Octanoic acid – fatty, rancid oil, cheesy• Decanoic acid – rancid, sour, fatty, citrus• Phenethyl acetate – Sweet, honey, floral rosy• Ethyl acetate – nail polish remover, solvent• Decanol – waxy, floral, orange, sweet

Wine Descriptions (under $25)• rose petal and earl grey tea, baking spices• pepper, baking spices, flowers• violets and spices• bittersweet iris-like, brioche as well as butter• black licorice and roasted herbs• mocha and anise• spice, licorice and wild bush, mineral • peppery spice, dust • fruit with nutty, savory complexity• popcorn, brioche, grilled nuts• smoke-accented aromas, cola and spices

Wine Descriptions ($25 to $50)• forest floor, black pepper, moss covered tree bark and game • potpourri and orange zest, with a subtle smoky overtone; spicy

floral, loamy earth, cedar and savory herb • Sappy, spice-accented, medicinal cherry note, with clinging

spicecake and cracked pepper• musky aromas, smoked meat, bacon fat and licorice and chocolate

flavors• smoky, savory; smoke and bacon with chocolaty finish; violets and

baking spices• bread crust, coffee and dark chocolate and a touch of spices• crushed rock, camphor, and a hint of pen ink• smoked meat, cracked pepper, tobacco and masses of crushed

stone / mineral• creosote, minerals, and toasty oak• incense and rose oil; sandalwood and tea leaf

Wine Descriptions ($50 to $75)• black truffles, roasted meats, charcuterie,

incense, roasted herbs and licorice; spice-accented aromas and potpourri, hint of spicecake; charcoal notes, long, tarry finish

• graphite, savory herbs, white flowers, orange peel, spices, nutmeg, clove; mineral and cedar; violet, grilled meat and tar, cassis and licorice

• bay leaf, sage, anise, toast and chocolate, mineral and earth; roasted coffee, herb; earthy black currant and fig, and charcoal-infused fruit

• exotic, smoky oak; sage and underbrush, even a touch of gun oil

Using Descriptors

• Wines were purchased from an online site by searching using descriptors from the aroma wheel

• These wines were tested for the presences of microbes by plating, microscopy, and qPCR

• Wines were also analyzed for 4EP and 4EG

What We Found• 35 wines were selected• 17 had viable lactic acid bacteria by plating

(49%)• 9 had viable Brett by plating • An additional 5 had Brett by qPCR• Another 4 had Brett by 4EP and 4EG levels• A total of 18 showed evidence of Brett (51%)• All of the wines were positive for microbial

contamination