Brett Character: Sensory Issues and Techniques

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Brett CharacterSensory Issues and Techniques

• Patricia Ann Howe
• ASCENT Laboratory and Consulting

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Sensory Issues- Outline

• Subjective vs Objective measurements
• Causative chemicals
• Headspace concentrations
• Thresholds
• Descriptive vocabulary
• Quality judgments
• Assigning cause and the associated baggage

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Subjective vs Objective

• Is all tasting subjective?

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subjective

• 4 a (1) peculiar to a particular individual
  PERSONAL ltsubjective judgmentsgt
• 4 a (2) modified or affected by personal views,
  experience, or background lta subjective account
  of the incidentgt
• 4 b arising from conditions within the brain or
  sense organs and not directly caused by external
  stimuli ltsubjective sensationsgt c arising out
  of or identified by means of one's perception of
  one's own states and processes lta subjective
  symptom of diseasegt -- compare OBJECTIVE 1c

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objective

• 1 d involving or deriving from sense perception
  or experience with actual objects , conditions,
  or phenomena ltobjective awarenessgt ltobjective
  datagt
• 3 a expressing or dealing with facts or
  conditions as perceived without distortion by
  personal feelings, prejudices, or interpretations
  ltan objective historygt ltan objective judgmentgt
• 3 b of a test limited to choices of fixed
  alternatives and reducing subjective factors to a
  minimum
• synonym see MATERIAL, FAIR

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Causative Chemicals

• What is Brett character, anyway?

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Brett character in wines

• 4 ethyl phenol from p-coumaric acid-Common
  descriptors include medicinal, phenolic, band
  aids, horse sweat, sweaty saddle, leather,or
  horse stable.
• 4 ethyl guaiacol from ferulic acid-
• Common descriptors include smoky, spent fire or
  fireplace, and spicy

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Mousiness (N-Heterocyclic Compounds)

• 2 acetyltetrahydopyridine (ACTPY)-associated with
  catabolism of L-lysine (and L-ornithine)
• 2 acetylpyrroline (ACPY)- associated with
  L-ornithine
• Both are produced by Dekkera-Brettanomyces and
  some lactic acid bacteria
• In low concentrations said to have a popcorn or
  cracker aroma

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Headspace Concentrations

• Can we relate concentration to what we perceive?

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Units of Concentration
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Headspace Concentration

• We dont smell the actual concentration of a
  compound in the wine
• We can only smell what is in the headspace ABOVE
  the wine
• The relationship between liquid concentration and
  headspace concentration is affected by many things

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Effects on Vapor Pressure and Evaporation

• Polar nature of the molecules and other
  intermolecular forces-polar molecules usually
  have lower vapor pressure
• Surface area-increases the rate of evaporation,
  not the actual vapor pressure
• Temperature-increases the rate AND affects vapor
  pressure by overcoming intermolecular forces
• Concentration of the vapor molecules above the
  liquid-if equilibrium is achieved the rate is
  constant

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Intermolecular Forces (Van der Waal Forces)

• Hydrogen bonding (strongest)
• Dipole-dipole (second strongest)
• Ion-Dipole
• London dispersion Forces (weakest)
• Ion-Ion (strongest interparticle force within
  compounds)

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Thresholds

• Everybody talks about them, but what are they?

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Thresholds

• Conceptual The minimum energy level required for
  perception.
• Empirical The level at which detection occurs
  50 of the time.
• Factual There is no one energy level below which
  detection never occurs and above which detection
  always occurs

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Complications in Finding Thresholds

• There is variability in the point at which
  observers change their response
• There is variability even within a single
  individual
• Even within the same experimental session, the
  point at which people change their responses will
  differ
• There are also differences between people

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Why Thresholds?

• A popular approach in flavor research is to
  presume that only those chemical compounds
  present in concentrations above their threshold
  will contribute to the perceived aroma.
• -Sensory Evaluation of Food Principles and
  Practices Lawless and Heymann (1998)

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Thresholds of Perception(Boidron, J.N, P
Chatonnet, and M. Pons 1988)all given in ppb
(ug/L)
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Ave Brett vs Ave 4 Ethyl Phenol
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Linear Regression for Taster F
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Linear Regression for Taster G
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Descriptive Vocabulary

• What can we say.

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Learning to Use Descriptive Vocabulary

• Practice-tasting is both physical and mental and
  requires training and practice.
• Use of standards-without standards, vocabulary
  cannot be developed and agreed upon. Standards
  provide a common and unifying experience.
• Spiked samples-a way to evaluate your performance
  at the actual time of tasting.

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Use of the Aroma Wheels

• Identify common wine aromas
• Group the aromas by similarity
• Easy to use, and easily understood
• Use analytical, not judgmental terms
• Terms are linked to physical standards
• Terms are NOT exclusive

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Descriptive Vocabulary

• We are not able to identify compounds
• We cannot say with absolute certainty that what
  we smell as horse sweat or band-aids is 4
  ethyl phenol
• We CAN say that it sure smells LIKE 4 ethyl phenol

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Quality Judgments

• Somebodys got to do it.

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Expert Tasters

• Wine Makers
• Wine Writers
• Masters of Wine
• Wine Critics

• Offer product quality judgments based on personal
  experience
• Offer quality judgments on the effects of
  particular treatments
• Very familiar with different wines

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Factors which influence the quality of an opinion

• Psychological biases
• Physical limitations
• Time constraints
• Conflicts of interest
• Personal desires
• External manipulations

• Self doubt
• Blind spots
• Ego
• Competition
• Incompetence
• Over thinking

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Causal Associations

• Is it human nature to find something to blame?

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Causal Associations

• We are not able to identify the source of aromas.
• We cannot say with absolute certainty that what
  we smell as horsey or band-aids is due to
  Brett growth.
• We CAN say that it sure is LIKELY from Brett
  growth.

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Causal Associations and Quality

• As winemakers, we are required to make causal
  associations from sensory input.
• As expert tasters, we are required to make
  quality judgments based on that same input.
• As human beings, it is difficult to not to mix
  the two functions and make causal associations of
  quality.

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Causal Associations and Quality

• As winemakers we taste something a little
  horsey LIKE 4 ethyl phenol. We assign cause
  Likely Brett infection.
• As expert tasters, our quality judgment is
  clouded by knowledge of possible future changes
  in the wine due to a likely infection.
• As human beings, this wine is less good if we
  are afraid of those changes, and better if we
  want to head that direction. The wine is NOT
  evaluated for what it is NOW.

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Brett CharacterSensory Issues and Techniques

• Patricia Ann Howe
• ASCENT Laboratory and Consulting