Altering the Chemical Profile of Sauvignon Blanc Wines to Match Consumer Preferences

Tip on reading my reviews:  If it’s getting too technical for you in the methods/results, or if you don’t have much time to read through everything, just read the bolded results and skip to the conclusions for a brief summary 😉

Many aromatic compounds, be they desirable or undesirable, are produced by yeasts during the fermentation process.  In Sauvignon Blanc wines, common compounds that are known to produce specific aromatic characteristics include the thiols 4-mercapto-4-methylpentan-2-one (4MMP) and 3-mercaptohexan-1-ol (3MH) and the acetate 3-mercaptohexyl acetate (3MHA).  These compounds often express characteristics of grapefruit, passionfruit and other tropical fruit.  Depending on concentration, these sensory characteristics may change; for example, at high concentrations, these compounds have been known to take on “sweaty”, box hedge, cat urine, or sulfur-like characteristics.

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Different yeast strains can produce different concentrations of these thiols, as well as acetates and ethyl esters, which would effectively change the sensory characteristics of the finished wine.  By inoculating with multiple yeast strains, the concentration of these thiols increase further and change the sensory characteristics of the finished wine even more.  Armed with this knowledge, winemakers have the ability to alter their techniques in the cellar in order to produce a very specific type of wine with specific desired sensory characteristics.

In regards to consumer preferences, studies have shown that the choice of yeast strain used in Sauvignon Blanc fermentation affected their preferences for the wines.  For example, one study found that most consumers enjoyed wine with an intermediate sensory profile compared to other wines in the study, and did not enjoy wines with high ester-like and fruity aromas (which were higher in thiols).  According to studies, these thiols plus 2-isobutyl-3-methoxypyrazine (IBMP) drive consumer preferences for Sauvignon Blanc wines.  IBMP is known to produce “green” characteristics in Sauvignon Blanc wines, though higher concentrations of the compound have less-than-desired aromatic effects.  Though much work has been done in this area, it is not known at what concentrations these compounds can be to produce a wine that is desirable to the market.

The goal of the study presented today aimed to determine what sensory characteristics shape consumer preferences for Sauvignon Blanc wines, and to examine the interactions between various key aromatic compounds that give rise to these different characteristics.

Methods

Aromatic compounds were added to a white base wine at different concentrations and combinations to create a 21 total samples.  The thiols added were 3MH, 3MHA, 4MMP, and IBMP were added to the base wine at both moderate and high concentrations.  Esters added were ethyl butanoate, isoamyl acetate, ethyl hexanoate, ethyl octanoate, and phenyethyl acetate.  Two enantiomers (a.k.a. configurations) of 3MH and 3MHA were also added (both R and S configurations)

The base wine used in this study was a 2009 Yalumba Classic Dry White bag-in-box wine.  The base wine had the following enological characteristics:  3.1g/L glucose + fructose, 3.26 pH, 6.5g/L titratable acidity, 0.3g/L volatile acidity, and 12.0% v/v alcohol.  96% v/v food grade ethanol was added to both the treatments samples and the control base wine in order for all samples to have the same ethanol content.  The following were measured for all samples: methoxypyrazines, acetate esters, ethyl esters, and thiols.

For the sensory analysis, 10 people were recruited (7 female, 3 male) all who had previous experience with white wine descriptive analysis research.  Individuals were selected from the local community (Adelaide, Australia) based ability to distinguish aroma and flavor in wine through difference testing, as well as smell and taste identification tests.  All individuals went through 5 training sessions, including three two-hour discussion sessions to determine wine attributes and how to use the scale, as well as two practice rating sessions before the actual experimental rating sessions began.

Wine samples were assessed during five sessions that lasted approximately 2 hours each.  Sessions occurred under sodium lighting in isolated and temperature-controlled tasting booths.  During each session, 18 samples were presented to the panel in sets of three, with rest breaks in between each sample and 15 minutes between each set of three.  Samples were presented randomly and balanced across all panelists. No samples were swallowed/consumed during the sessions.

To test consumer acceptance of the different wine samples, 7 of the 21 samples were analyzed.  Consumer acceptance testing occurred within a few weeks of the panelist sampling as described above.  Consumers were recruited by advertisements in a local newspaper as well as the Australian Wine Research Institute website.  In order to participate in the study, consumers had to be over the age of 18, regular white wine drinkers (consuming white wine at least once per week), regular white wine purchasers (between AUD$ 10-20), having no professional wine education, in good health, no allergies to any foods, and no ethical or medical reasons for not being able to consume alcohol.

Once deemed eligible to participate, each individual attended one of 12 hour long sessions.  The testing conditions were nearly identical between this session and the sensory analysis sessions described above.  7 samples were presented to participants with a three minute break between samples (with water rinsing).  Participants were asked to rate their “liking” for each sample on a conventional hedonic 9-point scale (from “dislike extremely” to “like extremely”).

There were a total of 150 participants, with 73 of them being female and 77 of them being male.  Questionnaires were also used to determine demographics of participants, as well as their wine usage and attitudes toward wine.  Wine knowledge was ranked from low to high, with those in between falling into the medium category.  Participants also ranked either liking of four different white wine styles; Riesling, Chardonnay, Australian Sauvignon Blanc, and New Zealand Sauvignon Blanc.

Results

Demographics

•       There was a relatively equal distribution for age and gender among participants.
•       There was a slight bias toward higher levels of education and higher household incomes among participants.
•       75% of participants were born in Australia, while most others were born in the United Kingdom.

Sensory Descriptive Analysis

•       7 aroma characteristics and 2 palate characteristics were significantly different among the 21 samples tested.

o   These were: overall fruit aroma, tropical, confectionary, cat urine/sweaty, fresh green, cooked green vegetal, solvent, citrus flavor, and green flavor.

•       There was a strong, positive correlation between “fresh green” and “green flavor”.
•       There was a strong, positive correlation between “overall fruit aroma” and “tropical”.
•        All samples containing IBMP (methoxypyrazine) were rated highly in “green” character, and rated low in “fruit” and “confectionary” characteristics.

o   The remainder of the samples (including the base wine) had relatively low ratings for “green” characteristics.

•       There was a positive correlation of the characteristics “solvent” and “citrus flavor”.
•       The base wine was not rated high for any specific characteristic, though it did have relatively high ratings for “solvent” and “citrus flavor”.
•       Samples with moderate levels of thiols (MHA: mercaptohexyl acetate; and MMP: mercapto-4-methylpentan-2-one; in particular) showed higher ratings for “overall fruit aroma”, “tropical” and “cooked green vegetal” characteristics compared with the base wine.
•        Samples with MH (mercaptohexan-1-ol) showed higher ratings for “citrus flavor” and “tropical”, and lower ratings for “cooked green vegetal” compared with the base wine.
•        Thiol combinations at moderate concentrations showed increased levels of “overall fruit aroma”, “tropical”, and “cooked green vegetal” compared with the base wine.

o   At higher concentrations, ratings for “cat urine/sweaty” and “cooked green vegetal” increased, while “overall fruit aroma” and “tropical” decreased, compared with thiols present at more moderate concentrations.

o   Results indicate that thiols can contribute to “green” characteristics in wine.

•       Thiol + high concentrations of  MHA sample had the highest rating of “cat urine/sweaty” compared to high concentrations of Thiol alone, and also displayed high levels of “”overall fruit aroma” and “tropical” characteristics.
•       Thiol + high concentrations of  MMP and Thiol + high concentrations of MH showed intermediate ratings in all characteristics and were usually lower than samples with moderate concentrations of thiols.
•        There was a positive correlation between 3MHA concentrations and “cat urine/sweaty” characteristics.
•       3MH and 4MMP did not contribute any specific sensory characteristics to thiols when at moderate or high concentrations.
•        Samples with higher levels of the S-enantiomer for thiols had more dominant effects on aroma characteristics than samples with higher levels of the R-enantiomer. (Reminder: enantiomer is a fancy word for “configuration”).

o   Sensory perception changes when the ratio of S- to R- enantiomers changes.

•       Thiol + Ester had higher ratings for “overall fruit aroma”, “tropical”, and “cooked green vegetal”, and had the highest rating for “confectionary” characteristics.
•       Ester combinations alone (no thiols) were similar to the base wine, but had higher ratings for the “confectionary” characteristic.

o   When combined with thiols, the “confectionary” characteristic remained high.

o   When combined with high concentrations of thiols, the “confectionary” characteristic decreased significantly.

§  Results suggest thiols suppress esters when present in high concentrations.

•       “Overall fruit aroma”, “tropical”, and “cooked green vegetal” increased with Thiols + esters at all concentrations and “cat urine/sweaty” increased with high concentrations of Thiols + esters.
•       Thiol + IBMP and high concentrations of Thiol + IBMP showed increased in “overall fruit aroma”, “tropical”, and “cooked green vegetal”, and a decrease in “fresh green” characteristics.

o   Thiols were able to suppress dominance of IBMP-induced “green” characteristics.

•       Holding the thiol concentration constant while doubling the concentration of IBMP resulted in significant increases of “fresh green”, “green flavor”, and “cooked green vegetal”, and decreases of “overall fruit aroma”, “tropical”, and “cat urine/sweaty”.

o   Results suggest a mutual suppression of methoxypyrazines and thiols on when another when in combination.

•       IBMP had a greater impact on sensory profiles of wine than thiols.

o   Results suggest there is a balance between dominance of IBMP and thiols that result in very different styles of wine, depending upon the concentrations of each compound.

Consumer Acceptance

•        Among the 7 samples tested, there were no significant differences in “liking”/consumer preferences.

o   There were trends, however, showing that samples with esters had the highest “liking” values, followed by samples with thiols, and finally the base wine and the samples with IBMP.

•        Analysis revealed three distinct groups of consumers related to their preferences.

o   Group 1 (26% of consumers) most “liked” the base wine (high in “solvent” and “citrus flavor” characteristics) and the combination of  high Thiol levels + high IBMP levels (high in “green” character).  Thiols alone were “liked” the least.

§  Positive associations found between “liking” and “solvent”, “fresh green”, and “green flavor” characteristics.

§  Negative associations found between “liking” and “overall fruit aroma”, “tropical” and “cat urine/sweaty” characteristics.

o   Group 2 (43% of consumers) most “liked” samples containing IBMP (high in “green” character).  Added esters and the base wine were “liked” the least.

§  Positive associations found between “liking” and “fresh green”, “cooked green vegetal”, and “green flavor” characteristics.

§  Negative associations found between “liking” and “solvent” and “citrus flavor” characteristics.

o   Group 3 (31% of consumers) most “liked” samples with esters (high in “overall fruit aroma”, “tropical”, “cat urine/sweaty”, and “confectionary” characteristics). IBMP and base wine were “liked” the least.

§  Positive associations found between “liking” and “confectionary”, “overall fruit aroma”, and “tropical” characteristics.

§  Negative associations found between “liking” and “fresh green”, “cooked green vegetal”, and green flavor” characteristics.

•       The strongest drivers of “liking” or “not liking” for all groups were “confectionary”, “cat urine/sweaty”, and green characteristics such as “fresh green” and “green flavor”.
•       There was a strong difference between consumers that preferred “green” characteristics and consumers that preferred “fruity” characteristics.

Demographics/Consumer Preference Behavior

•       Group 2 had equal numbers of males and females, Group 1 had more males than females, and Group 3 had more females than males.
•       There were differences between the liking of and consumption of New Zealand Sauvignon Blancs and red wine consumption.

o   Group 2 liked New Zealand Sauvignon Blanc significantly more than Group 1.

o   Groups 2 and 3 had a larger percentage of consumers drinking three or more glasses of NZ Sauvignon Blanc per week than Group 1.

o   Group 3 consumers drank significantly less red wine per week than consumers in Group 1 or 2.

•        Group 2 had the largest percentage of consumers with low wine knowledge, Group 3 had the largest percentage of consumers with moderate wine knowledge, and Group 1 had the largest percentage of consumers with high wine knowledge.
•       Group 2 consumers (with lowest wine knowledge) preferred wines with “green” characteristics.
•       Group 3 consumers (with more moderate wine knowledge) preferred wines with “fruity” characteristics.
•        Group 1 consumers (with the highest wine knowledge) did not appreciate high “fruity” wines.

Conclusions

According to the authors, the results of this study show that there is a strong dominance of methoxypryazines in combinations with thiols, and also an enhancing effect of esters in white wine.  Specifically, thiols were able to suppress sensory effects of methoxypryazines and esters when present at high concentrations.  The sensory analysis suggest that winemakers may use methoxypyrazine levels in grapes and wine as an approximate estimation of “green” characteristics in wine, which would help create a specific type of wine with particular sensory attributes.

The authors claim that this is the first study to show the direct effects of aromatic compounds on wine quality as perceived by wine consumers.  They found that there is no one single aromatic characteristic that drives consumer preferences in regards to Sauvignon Blanc wines, and that consumer preferences are very complex.  The results clearly show that it is extremely difficult to predict consumer acceptable of Sauvignon Blanc based on any one particular characteristic alone. 

However, since the results did show that there are clear group preferences among consumers in regards to Sauvignon Blanc wines, winemakers should be able to take what has been found regarding the chemistry, sensory, and preference analyses, to create different types of Sauvignon Blanc wines that are tailor-made for any particular group of consumers.

I’d love to hear what you all think of this study!  Please feel free to comment below (Reminder: any unapproved HTML tags will be promptly removed).

Source: King, E.S., Osidacz, P., Curtin, C., Bastian, S.S., and Francis, I.L. 2011. Assessing desirable levels of sensory properties in Sauvignon Blanc wines – consumer preferences and contribution of key aroma compounds. Australian Journal of Grape and Wine Research 17: 169-180.

DOI: 10.1111/j.1755-0238.2011.00133.x

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