1. Aromatic Defects in Wine

2. Wine Defects Defects Part I Defects Part II Acetaldehyde, oxidation
Cork taint, TCA
VA I, acetic acid
Brettanomyces 1
VA II, ethyl acetate
Brettanomyces 2
Lactic taint
Methoxypyrazine
Hydrogen sulfide
Microbial

3. Oxidation Oxygen is essential for fermentation
Beneficial during maturation in small quantities for most dry reds, some whites
Over exposure of oxygen in must and wine results in
Browning, general shift in color
Loss of fruit characteristics
Development of oxidized aromas and flavors
Some wines however require excessive oxygen to develop their characteristic style. These include: ?

4. Acetaldehyde Causes
During fermentation, acetaldehyde (CH3CHO) is a precursor to ethanol production
Almost all is subsequently converted into ethanol (C2H5OH)
Presence of acetaldehyde in a finished wine often indicates an excess of oxidation or spoilage caused by aerobic film yeast
Impacts white wines more than reds
Can be smelled in as small a quantity as 1.5 ppm
Has a nutty, sherry like aroma
May react with anthocyanin pigments to shift the red color towards blue
Excessive SO2 at fermentation may contribute to its production

5. Oxidation and Acetaldehyde
Prevention
Moderate SO2 dose at fermentation and keep pH low
Careful control over CO2 levels in white and reds following fermentation
Minimize aeration during transfer (racking, bottling) by using inert gas (CO2, argon, nitrogen) ?
Treatment

6. Volatile Acidity I – Acetic Acid Causes
Volatile acidity will vaporize with steam heat unlike other acids present in wine.
Acetic acid is almost always the result of bacteria
Acetobacter require oxygen to survive and grow
Causes of acetic acid may be from
Exposure of must/cap to air during fermentation
Unsanitary containers or containers infected with bacteria
Initial high brix must followed by an incomplete fermentation
Spoilage by lacto bacillus
Over exposure during maturation
Surface/film yeast on the wine
Poor SO2 management

7. Volatile Acidity II – Ethyl Acetate Causes
Ethyl acetate is an ester of ethyl alcohol and acetic acid
Threshold sensory level for most people is 150–200 mg/L
Acetobacter in the presence of oxygen may develop EA
Causes of ethyl acetate may be from high levels of acetic acid due to
Unsanitary fermentation containers and tools
Poor fermentation technique – excessive exposure of must/cap to air during fermentation
High pH and wines with little SO2 (acetobacter are sensitive to SO2 )
Stuck wines – wines with residual sugar
Excessive exposure of wine to air during maturation.
Lactic acid or acetic acid spoilage
Sound wines will not generate VA once bottled.

8. Volatile Acidity (VA) I, II Treatment / Prevention?

9. Lactic Taint Causes Lactic taint or souring
Lactic bacteria other than ML bacteria metabolizing malic acid
Lactobacillis and Pediococcus
Malolactic fermentation, when undesirable in white wines
Wine is often spritzy and turbid with odors such as
Spoiled milk/buttermilk
Sourdough
Fermenting cabbage
Excessive diacetyl, producing soured buttery aromas
Sound wines may generate LT once bottled if residual malic acid is present.

10. Lactic Taint Prevention
Strive for low pH and good SO2 management
Proper hygiene, clean and/or pasteurized equipment
Use lysozyme addition and/or sterile filtration to curtail or prevent ML fermentation
Use fresh bacteria cultures from dependable sources if ML is desired. Monitor results
Treatment, ?

11. Hydrogen Sulfide Not sulfite. Sulfide threshold is 5 ppb
Hydrogen sulfide, mono and di-mercaptans
As a flaw, may be mistaken for varietal or regional character “terroir.”
Odors range from slightly complex aroma, rotted cabbage, tires, or sewage.
Usually associated with stressed yeast and low nitrogen levels during fermentation.
Causes include --
Free sulfur/late sulfur spray on grapes.
Some yeast strains produce more than others but all yeast produce H2S.
Insufficient nitrogen for fermentation
Elemental sulfur inside barrels
May become more complex, harder to treat as the wine ages

12. Hydrogen Sulfide Prevention
Proper nutrients for yeast added at appropriate timing sequences before and during fermentation
(Follow supplier’s recommendations)
Use appropriate and healthy yeast strains
Avoiding fruit with free sulfur-containing compounds
Avoid heavy layer of sediment in wine containers
Monitor wine throughout fermentation and maturation for sulfide odors and correct early

13. Hydrogen Sulfide
Treatment – ? Concerns

14. Cork Taint As many as 10% of bottles may exhibit taint
Cause – is the chemical compound, 2,4,6- trichloroanisole or TCA
Produced by mold spores digesting phenol in the presence of chlorine used to clean raw cork
TCA can occur/develop during manufacturing or in the cellar
Prevention
Never allow chlorine products in the winery
Sample corks to screen for TCA
Treatment
There are a few costly proprietary processes ( ?

15. Brettanomyces Causes
Spoilage yeast, commonly found in wines, primarily reds
Yeast are resistant to moderate levels of SO2, low alcohol
Can feed off of small amounts of residual sugar in wine or present in the wood of a barrel (ideal environment)
Odor and flavors may increase over time and may resemble
horse stable, plastic, Bandaid ® (4-ethyl phenol)
smoked bacon, spice or cloves
sweaty animals, cheese and rancidity
wet dog, creosote, burnt beans, rotting vegetation,
mouse cage, mouse urine

16. Brettanomyces Causes Dominates or destroys the fruit of the wine
In minute amounts may add complexity.
“Brett” is a slow growing yeast that does not compete well against other micro-organisms.
Second use (or older) oak barrels aid in its colonization
Temperatures which encourage ML fermentation also aid in Brett to increase in population in the wine
Dissolved oxygen from frequent topping off help this yeast grow
Prevention
Use only clean or new barrels
Maintain hygiene and consistent SO2 management
Treatment ?

17. Microbial Causes
Generic yeast and bacteria spoilage of wine other than those mentioned
Usually the result of
Warm temperature of fruit arriving at the winery
Contamination from unsanitary condition
Low TA, high pH wines with residual sugar
Warm environments with dissolved oxygen
Retaining heavy lees following fermentation
Inconsistent or improper SO2 management
Residual sugar and or nutrients that support microbial growth
Residual malic acid or protracted ML fermentation
Prevention ? Treatment?

18. Methoxypyrazine Causes
Commonly referred to as an overpowering, unpleasant vegetative odor in wine
Light to moderate case: green bell pepper, fresh leaves
Worst case: Crushed lady beetle odor
Threshold of 10 to 15 parts per trillion¹
More common in cooler vintages or climates, lack of ripeness, physiologically immature, harsh tannins
Levels seem to decrease with fruit ripening
Typically levels do not decrease, degrade, with bottle aging
More common in some varietals (sauvignon Blanc) than others
Can also be attributed to crushed insects such as lady bugs
1. Roujou de Boubee, D., 2003 Amorim Academy Grand Prix

19. Methoxypyrazine Prevention Vineyard selection Vineyard management
Neither too low nor high a cropping level (vine balance)
Appropriate level of sun exposure in the canopy
Vineyard management
Decreasing water between fruit set and véraison
Harvest management
Avoid fruit with lady bugs
Thoroughly inspect all fruit before it enters the crusher
Treatment ?

20. Wine Defects – Notes Defect Source Characteristic Aroma Oxidation
Oxygen
VA I, Acetic Acid
Biological
VA II, Ethyl Acetate
Lactic Taint
Hydrogen Sulfide
Sulfur
Cork Taint
Environ
Brettanomyces I (Ethylphenol, 150 ppb)
Brettanomyces II
(Isovaleric acid)
Microbial
Methoxypyrazine