Wine and Juice Oxidation

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Wine and Juice Oxidation

• Patricia Howe
• March 2009

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Part I
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What is oxidative spoilage?

• In grape juice and wine, oxidative spoilage can
  mean several things
• Color becomes brown
• Fruit flavors are masked or muted
• Distinctive aromas are produced
• Sample A
• Sample B
• Sample C
• Sample D

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Describe the compounds

• Sample A Acetaldehyde
• Bruised apple, apple-like, nutty, citrus-like

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Describe the compounds

• Sample A Acetaldehyde
• Bruised apple, apple-like, nutty, citrus-like
• Sample B Acetic acid
• Vinegar, pungent

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Describe the compounds

• Sample A Acetaldehyde
• Bruised apple, apple-like, nutty, citrus-like
• Sample B Acetic acid
• Vinegar, pungent
• Sample C Ethyl acetate
• Nail polish remover, fruity, acetone

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Describe the compounds

• Sample A Acetaldehyde
• Bruised apple, apple-like, nutty, citrus-like
• Sample B Acetic acid
• Vinegar, pungent
• Sample C Ethyl acetate
• Nail polish remover, fruity, acetone
• Sample D Ethanol
• Warming, irritating, sweet, vodka-like

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Oxidation in Juice and Wine

• How is ethanol converted to these oxidized
  compounds?
• What are the mechanisms in wine and juice?
• How do these reactions and byproducts affect wine
  and juice?
• Are these reactions always bad for the wine?
• How do we prevent or encourage these reactions?

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Generalized Sequence of Chemical Oxidation (a
review)
Alcohol
Aldehyde
Acid
Alkane
--CH2OH
--COOH
--CH3
--CHO
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Generalized Series of Chemical Oxidation (a
review)
R any alkyl or aryl group
ROOH
RHO
RH2OH
RH3
Alcohol
Aldehyde
Acid
Alkane
CHO
COOH
CH2OH
CH3
Formaldehyde (Methanal)
Formic Acid (Methanoic Acid)
Methanol
Methane
CH3COOH
CH3CH3
CH3CHO
C2H5OH
Acetic Acid (Ethanoic Acid)
Acetaldehyde (Ethanal)
Ethane
Ethanol
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Oxidation of Juice and Wine

• How do you get from ethanol in wine to the
  oxidized aroma flaws?
• Will a bottle of ethanol sitting on the counter
  with oxygen spontaneously turn into sherry or
  vinegar?

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Oxidation of Juice and Wine

• How do you get from ethanol in wine to the
  oxidized aroma flaws?
• Will a bottle of ethanol sitting on the counter
  with oxygen spontaneously turn into sherry or
  vinegar?

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Modes of Wine Juice Oxidation

• Three distinctly different modes
• Enzymic- (enzymes)
• Chemical- (phenols and metals)
• Microbiological- (specific microbes and
  nutrients)
• Oxygen is initially required, but may be consumed
  during the process
• These reactions will produce the oxidative flaws
  of browning, acetaldehyde, acetic acid, and/or
  ethyl acetate
• These reactions can also be controlled or
  encouraged

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Part II
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Enzymic Browning

• An enzyme is a large protein which can catalyze a
  chemical reaction they are biological molecules
  produced by living organisms, but can react
  independently.
• The enzymes which cause browning in grape juices
  and wines facilitate reactions between oxygen
  dissolved in the liquid and a class of compounds
  known as phenols.
• Enzymic reactions are temperature dependent, and
  will increase as the temperature increases

Learn more about enzymes and phenols in the
reading
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Phenols

• Phenols are a general class of aromatic compounds
  that contain one or more hydroxyl groups.
• Phenolic substrates in grapes include catechin,
  chlorogenic acid, catechol, caffeic acid, DOPA,
  tannins, flavonols, protocatechuic acid,
  resorcinol, hydroquinone, phenol
• In winemaking, phenolic compounds dictate the
  color, astringency, and bitterness of the wine.

The chemical structure term aromatic refers to
the ring structure with alternating bonds, (a
benzene ring) which may have been named for its
perfumy scent. The OH is called a hydroxyl
group The circle and the alternating bonds are
ways of showing the same thing.
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Enzymic Browning

• Inherent enzymes in the grape, polyphenol
  oxidases
• Same enzyme which causes browning in apples
• This enzyme is destroyed by alcohol and can be
  controlled with sulfur dioxide there is also a
  pH effect, with low pH slowing the reaction.
  High heat will denature the protein.
• These enzymes can brown the juice of the grapes,
  but can not continue to brown in the wine.

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Enzymic Browning

• Enzymes from molds which can infest the grape -
  laccases
• These enzymes can function in alcoholic solutions
  and so can brown a finished wine
• Sulfur dioxide is not very effective against
  these enzymes
• Dessert wines styles such as Sauternes and
  Ausleses (made from intentionally moldy grapes
  from nobel rot, Botrytis cineria) are usually
  noticeably brown

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Chemical Oxidation of Wine

• Occurs in
• poorly sealed bottles or tanks
• the production of baked sherries, which uses heat
  to speed these oxidative reactions
• an open glass of wine sitting for extended
  periods (days or weeks), assuming no microbes
  begin to grow

• The increased solubility of oxygen at colder
  temperatures can counteract the slower reaction
  rate at lower temperatures.
• Does not involve enzymes or microbes

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Chemical Oxidation in Wine
Acetaldehyde
Ethanol
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Chemical Oxidation in Wine
Acetaldehyde
Ethanol
C2H6O
C2H4O
Text formulas
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Chemical Oxidation in Wine
Acetaldehyde
Ethanol
C2H6O
C2H5OH
C2H4O
Text formulas
CH3CH2OH
CH3CHO
CH3CH2OH
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Chemical Oxidation in Wine
Acetaldehyde
Ethanol
C2H6O
C2H5OH
C2H4O
Text formulas
CH3CH2OH
CH3CHO
CH3CH2OH
Lewis structures
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Chemical Oxidation in Wine
Acetaldehyde
Ethanol
C2H6O
C2H5OH
C2H4O
Text formulas
CH3CH2OH
CH3CHO
CH3CH2OH
Lewis structures
Skeletal formulas
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Chemical Oxidation in Wine

• In wines, chemical oxidation occurs
• When dissolved oxygen reacts with a specific type
  of compound (usually a dihydroxy phenol) to form
  a peroxide molecule
• A coupled reaction involving the peroxide and
  ethanol results in the production of acetaldehyde
• Copper or Iron ions are required as catalysts

Learn more about phenols and wine oxidation in
the reading. Active research continues in this
area
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Auto-oxidation
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About copper or iron.

• Does a bottle of ethanol, with oxygen and with
  added phenolic compounds sitting on the counter
  spontaneously oxidize?

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About copper or iron.

• Does a bottle of ethanol, with oxygen and with
  added phenolic compounds sitting on the counter
  spontaneously oxidize?

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About copper or iron.

• Does a bottle of ethanol, with oxygen and with
  added phenolic compounds sitting on the counter
  spontaneously oxidize?

Cu or Fe
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About copper or iron.

• Does a bottle of ethanol, with oxygen and with
  added phenolic compounds sitting on the counter
  spontaneously oxidize?

Cu or Fe
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Esters and Esterification

• An ester is a molecule made by a reaction
  combining an Alcohol with an Acid.
• This reaction is called esterification
• Most esters are have fruity smells and are common
  in foods and beverages.

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Common Esterification in Wine
Acetic Acid
At wine pH
Ethanol
Acetate ion
Ethyl acetate
H2O
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Part III
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Microbiological Oxidation

• Several genera of yeast and bacteria can convert
  grape sugars (in juice) or ethanol (in wine) into
  acetaldehyde, acetic acid, and/or ethyl acetate.
• Some of these microbes are sensitive to ethanol
  and do not grow in wine
• Most are sensitive to sulfur dioxide
• Most grow better at warm temperature than at
  cooler temperatures.

Kingdom-gt Phylum-gtClass-gtOrder-gtFamily-gt
Genus-gtSpecies
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Surface films in wine
This is usually a sign that some type of
microbial oxidation is occurring, because of the
location at the air/liquid interface.
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Oxidative Yeast Common in Wine and Juice

• Alcohol tolerant
• Saccharomyces (specifically Film species)
• Candida (surface yeasts)/Metshnikowia
• Saccharomycodes
• Zygosaccharmyces
• Brettanomyces/Dekkera
• Shizosaccharomyces
• Alcohol Sensitive
• Kloeckera/Hanseniaspora
• Pichia

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Yeast Metabolism
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Some Common Wine Yeasts100x magnification
Courtesy of UC Davis Dept VEN
Dekkera
Brettanomyces
Saccharmomyces
Pichia
Kloeckera
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Oxidative Bacteria in Wine and Juice

• Acetic Acid Bacteria
• Strict Aerobes
• Acetobacter aceti
• Acetobacter pasteurianius
• Gluconobacter oxydans (mostly fruit and juice)

• Lactic Acid Bacteria (LAB)
• Facultative Aerobes
• (Hetero Homo Fermentative)
• Oenococcus oeni
• Lactobacillus species
• Pediococcus species

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Homo- and Hetero- Fermentative LAB

• homofermentative
• produce more than 85 lactic acid from glucose.
• heterofermentative (type I)
• produce only 50 lactic acid and considerable
  amounts of ethanol, acetic acid and carbon
  dioxide.
• heterofermentative (type II)
• produce DL-lactic acid, acetic acid and carbon
  dioxide.

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LAB Metabolism
Oenococcus slightly aerated lactate and ethanol
aerated lactate and acetate
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Some Common Wine Bacteriaelectron microscope
photos from Jeff Broadbent Utah State University
Lactobacillus casei
Oenococcus oeni
Lactobacillus delbrueckii
Pediococcus pentosaceus
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Part IV
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Primary Sources of Wine and Juice Oxidation
byproducts

• Browning
• Enzymic and Chemical
• Acetaldehyde
• Chemical and Microbiological
• Ethyl Acetate
• Chemical and Microbiological
• Acetic acid
• Microbiological
• there is another source of acetic acid in wine
  which we will learn more about when we discuss
  oak barrels

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Preventing Oxidation Juice

• Process fruit free of molds and rots
• If mold is present, sort fruit to remove moldy
  clusters
• consider a juice treatment to remove/denature the
  laccase enzymes (ie bentonite or pasteurization)
• Control juice O2 levels if browning is a concern
• Maintain SO2 levels appropriate to pH
• Control temperature (colderslower reactions)
• Avoid higher pHs (phenol chemistry)
• Use good cleaning sanitation practices
• Monitor microbe levels

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Preventing Oxidation Wine

• Maintain SO2 levels appropriate to pH
• Control temperature (colderslower reactions but
  higher potential dissolved oxygen)
• Avoid higher pHs (phenol chemistry)
• Use good cleaning sanitation practices
• Monitor microbial levels
• Reduce O2 levels in wine,
• During storage, keep containers full
• During bottling, use inert gases or other methods
  to reduce O2 pickup
• Use inert gases during transfers and other wine
  work.

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The distribution of species of sulfurous acid at
various pH values. (From Ough,
1984)                
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Free SO2 to reach molecular SO2 by pH
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What is Controlled Oxidation?

• Deliberate (or intended, or not prevented)
  addition of air or oxygen to juice
• Deliberate (or intended but not controlled) very
  slow and minor additions of air or oxygen
• Stabilized or improved color, reduce phenols,
  reduce some aromas
• Reduction in astringency, harshness, or green
  and unripe tannin flavors.
• Possible reduction in green or vegetal aromas

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Controlled Enzymic Oxidation?

• In grape juice, controlled enzymic oxidation can
  result in several things
• Brown pigments become too large to remain
  soluble phenol levels are lower in the wine
• Undesired aromas may be changed, masked, or
  eliminated
• May affect pinking precursors

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Controlled Chemical Oxidation

• In wine, controlled chemical oxidation is a slow
  addition of extremely low levels of oxygen
• It must not manifest as a flaw
• Traditional Barrel Aging with resulting slow
  exposure to oxygen through bungs or staves
• Traditional Bottle aging, with resulting slow
  exposure through residual oxidation or permeation
  through closure, resulting in bottle bouquet
• Controlled micro-oxidation or MOX systems
• Heating with air to produced baked sherries

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Controlled Microbial Oxidation

• The bacteria Acetobacter aceti converts ethanol
  into acetic acid in the vinegar process.
• Balsamic vinegar is produced by growing
  Zygosaccharomyces bailii in concentrated grape
  juice (not wine). The yeast converts the sugar
  in the juice directly into acetic acid.
• Flor style sherries are produced by growing
  special Saccharomyces cerevisea (beticus,
  cheresiensis, montuliensis or rouxii) yeasts in
  higher alcohol wines the alcohol is converted
  into acetaldehyde.

Genus species
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Wine and Juice Oxidation

• Patricia Howe
• March 2009