wine defects workshop - ucanr.edu

WINE SENSORY DEFECTS

Sue Langstaff

Applied Sensory, LLC

OUTLINE

Definition of Defect

Thresholds

Origin and description of

wine sensory defects (faults)

OUTLINE

Examples of aroma defects

Possible treatment

Possible prevention

The first difficulty that tasters

encounter is to find and to

translate into precise and clear

language the qualities and defects

of a wine...

Pierre Bréjoux

SENSORY DEFECT

Value judgment

Attribute not wanted

SENSITIVITY

The degree to which an

observer is responsive to a

stimulus at or near threshold

THRESHOLD - DEFINITION

A concentration range exists below

which the odor of a substance will

not be detectable under practical

circumstances, and above which

individuals with a normal sense of

smell would readily detect the

presence of the substance

PROBABILITY FUNCTION

THRESHOLDS

• Define “perceptible” levels for

taints or off-flavors in products

• Screen individuals for their

sensitivity to key components

Uses:

AROMA DEFECTS

1. ACETALDEHYDE

2. VOLATILE ACIDITY

(ACETIC ACID, ETHYL ACETATE)

3. CORK TAINT (TCA)

AROMA DEFECTS

4. SULFUR-DERIVED COMPOUNDS (H2S)

5. ORGANIC SULFUR-CONTAINING

COMPOUNDS (MERCAPTANS)

6. BRETTANOMYCES

7. MOUSEY TAINT

AROMA DEFECTS

Smells like:

(threshold values

NOT given)

Comes from:

AROMA DEFECTS

Possible treatment:

Possible prevention:

AROMA DEFECTS

ACETALDEHYDE

ACETALDEHYDE

• Over-ripe bruised apples

• Sherry

• Nut-like

ACETALDEHYDE

Comes from:

1. Wine aging

Chemical oxidation (+O2)

of ethanol

ACETALDEHYDE

Associated with:

• Increased color depth in

white wines

• Brickish tint in red wines

“OXIDATION”

“Oxidized” character often

due to high concentration

of acetaldehyde

ACETALDEHYDE

• Surface (flor or film) yeast

growing aerobically may

oxidize ethanol to acetaldehyde

2. Improperly stored wines

ACETALDEHYDE

• Growth of oxidative

bacteria on wine surface

ACETALDEHYDE

Treatment:

• Add SO2 in increments

until free SO2 begins

to decrease

ACETALDEHYDE

Prevention:

• Inoculate with known cultures

• Control spoilage organisms

• Provide adequate nutrition for organisms

• Monitor critical parameters throughout winemaking process

• Practice good cellar hygiene and sanitation procedures

• Avoid cross contamination of equipment and wine

• Use SO2 appropriately

• Keep containers topped

• Limit oxygen exposure of must/wine

AROMA DEFECTS

VOLATILE ACIDITY

acetic acid ethyl acetate

VOLATILE ACIDITY (VA)

• Vinegar (aa)

• Fingernail polish (EtAc)


Comes from:

1. Yeast

Many non-Saccharomyces

strains able to produce

relatively large amounts of

acetic acid and esters


Influenced by:

• Strain

• Fermentation temp.

• Juice composition

Normal by-product of

Saccharomyces growth


2. Heterofermentative

lactic acid bacteria during

primary fermentation


• Metabolism of citrate by

Oenococcus oeni leads

to formation of VA

• Acetyl-phosphate oxidized

to produce acetic acid


3. Acetic acid bacteria (aerobic)

• Acetobacter species of choice

for commercial vinegar (acetic

acid) production

• Also produces ethyl acetate


Post-fermentation sources:

1. Cellar practices

Allowing ullage

(headspace in barrels)


“Acetic aroma” not

exclusively a result of

acetic acid


Acetate esters (ethyl

acetate) contribute

significantly to this defect


Esters:

Volatile compounds

formed by combination of

an alcohol and an acid


ETHYL ALCOHOL + ACETIC ACID ETHYL ACETATE + WATER

CH3CH2-OH + HO-C-CH3 CH3CH2 -O-C-CH3 + H2O


Treatment:

• Acetic acid - reverse osmosis

• Ethyl acetate - difficult to correct


Prevention: • Inoculate with known cultures









• Sterile filter, if necessary or desired

• Store wines in cool, dry area

• Control insects

AROMA DEFECTS

CORKINESS

AND

CORK TAINT

CORKED

• Musty

• Moldy

• Dank cellar

• Wet cardboard,

wet newspaper

CORKED

Comes from:

Phenol (cork) + chlorine

2,4,6-trichloroanisole (TCA)

mold

CORKED

Chloroanisoles not naturally

occurring in wine

Wine contamination requires

contact or storage with other

contaminated material

CORKED

TCA most often associated with

corks

Genuine cork taint results from

migration of TCA from

contaminated cork to bottled wine

CORKED

TCA contamination from other

wood materials:

• contact of wood with chlorine

• mold activity

CORKED

Other compounds:

• Geosmin (earthy, muddy)

• 2-methylisoborneol (cooked

beets, moldy)

• Guaiacol (smoky, spicy)

CORKED

Treatment:

• TCA can be removed from

wine with proprietary

methods using plastic

CORKED

Prevention:

• Screen in-coming corks

(sensory and instrumental)

• Eliminate chlorine from the

winery

AROMA DEFECTS

SULFUR-DERIVED

COMPOUNDS

SULFUR

• To yeast in protein

biosynthesis, vitamins

and coenzymes

S in various forms important:

SULFUR

• From a sensory standpoint

Volatile S compounds with

intense and disagreeable

odors

SULFUR

• Sulfate (SO42-)

• Sulfite (SO32-)

• Amino acids (methionine,

cysteine, cystine)

Available as:

SULFATE

Once inside cell, sulfate must

be reduced to lower

oxidation state to be useful

to cell

Yeast need sulfate to

support cell growth

HYDROGEN SULFIDE

• Rotten eggs

HYDROGEN SULFIDE

Comes from:

1. Yeast (sulfate

reduction pathway)

Most important source

quantitatively

HYDROGEN SULFIDE

• Can prevent its formation if:

Not stressed

Correct nutrition

• Integral part of metabolism

HYDROGEN SULFIDE

2. Elemental sulfur

Fungicide in vineyards

HYDROGEN SULFIDE

Levels dependent on:

Kind and amount

of elemental sulfur

on grapes

HYDROGEN SULFIDE

Yeast strains and

physiological condition

during fermentation

HYDROGEN SULFIDE

Low H2S producers:

Pasteur Champagne,

Epernay 2, Prisse de Mousse

Montrachet produces higher levels

HYDROGEN SULFIDE

Juice/wine chemistry

• pH

• Utilizable nitrogen levels

• Levels of sulfite and sulfate

• EtOH concentration

HYDROGEN SULFIDE

Physical parameters • Suspended solids

• Fermentation temp.

HYDROGEN SULFIDE

Oxidation-reduction

state of must and wine

Environmental factors

HYDROGEN SULFIDE

H2S can react with alcohol

to form mercaptans

Mercaptans can combine to

form disulfides which can’t be

removed from wine

“REDUCTION”

“Reduced” character due to

reduced sulfur compounds

such as H2S and mercaptans

HYDROGEN SULFIDE

Treatment:

• At primary fermentation: H2S + Air

• Copper fining addition with an inactivated

yeast product (generally successful

depending on when performed)

HYDROGEN SULFIDE

Prevention:





• Discontinue use of S-containing vineyard sprays 3

weeks prior to harvest

• Rack new wines off heavy primary lees in first

week fermentation has stopped

AROMA DEFECTS

ORGANIC

SULFUR-CONTAINING

COMPOUNDS

THIOETHER OR SULFIDE

-C-S-C-

Sulfur analog of ether

THIOL OR MERCAPTAN

-C-SH

Sulfur analog of alcohol

ETHANETHIOL (ethyl mercaptan)

• Onion

• Rubber

• Natural gas


Treatment:

Mercaptan + Mercaptan Disulfide

Copper fining NOT possible H5C2-S-S-C2H5

H2S + Alcohol Mercaptan

Copper fining possible H5C2-SH


Mercaptans + Air Disulfides

Aeration NOT a good idea

Disulfides in bottle Mercaptans

Thiols may re-form over time


Prevention:





• Discontinue use of S-containing vineyard sprays 3

weeks prior to harvest

• Rack new wines off heavy primary lees in first

week fermentation has stopped

AROMA DEFECTS

BRETTANOMYCES/

DEKKERA

BRETT.

• Barnyard

• Horse (blanket,

sweat, saddle)

• Wet dog

BRETT.

• Tar

• Tobacco

• Creosote

• Plastic

• Leather

• Pharmaceutical

(medicine chest,

Band-Aid)

There are people who have been

known to prefer bad wine to

good, just as there are men who

are fascinated by bad women.

André L. Simon

VOLATILE PHENOLS OF BRETT.

4-ethyl guaiacol (smoky)

4-ethyl phenol (medicinal)

BRETT.

Comes from:

Spoilage yeast

• Air

• Grapes ?

• Cellar (surfaces, equip.)

• Cooperage (prime source)

BRETT.

Treatment:

• 4-EP and 4-EG can be

reduced (but not eliminated)

with filtration/adsorption

BRETT.












• Control insects

FLAVOR DEFECTS

MOUSEY TAINT

MOUSEY TAINT

Aftertaste:

• Mouse urine

• Rancid nuts

MOUSEY TAINT

Comes from:

1. Brettanomyces (rarely)

2. Lactobacillus (usually)

Produced in presence of

lysine and EtOH

2-acetyl-3,4,5,6-

tetrahydropyridine

2-acetyl-1-pyrroline

MOUSEY TAINT

Treatment:

• None known

MOUSEY TAINT












• Control insects

TAKE-HOME POINT

Just because you don’t

smell (or taste) something

“bad” doesn’t mean that the

chemical(s) is (are) not

present in the wine

TAKE-HOME POINT

The concentration of the

chemicals may be below

your level of sensitivity

OR

TAKE-HOME POINT

The chemicals have not yet

combined with others to

form off-aromas or flavors

OR

TAKE-HOME POINT

Everything may be fine!

It is best to prevent

problems in the first

place than to try and

correct them in the wine!

wine defects workshop - ucanr.edu

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