Improvement of sensory quality control in PDO products: An example with txakoli white wine from Bizkaia

Food Quality and Preference 23 (2012) 138–147

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Improvement of sensory quality control in PDO products: An example with txakoli white wine from Bizkaia I. Etaio, P.F. Gil, M. Ojeda, M. Albisu, J. Salmerón, F.J. Pérez Elortondo ⇑ Laboratorio de Análisis Sensorial Euskal Herriko Unibertsitatea (LASEHU), Universidad del País Vasco – Euskal Herriko Unibertsitatea (UPV/EHU), Avenida Miguel de Unamuno ibilbidea 3, 01006 Vitoria-Gasteiz, Spain

a r t i c l e

i n f o

Article history: Received 8 November 2010 Received in revised form 3 February 2011 Accepted 21 March 2011 Available online 26 March 2011 Keywords: Sensory quality PDO Quality control Txakoli wine Certification

a b s t r a c t PDO products present some special features related to several factors. Among them, sensory characteristics are especially relevant. However, the sensory characteristics that differentiate each PDO products from the others are not usually described, so the criteria for sensory certification are not detailed enough and generic score cards are used. The work described in this article explains the process carried out to improve the sensory quality control of PDO Bizkaiko txakolina – txakoli de Bizkaia wine, with the aim of having available a specific method that considers the particularities of this product. In this sense, the method developed go further than the simple rejection based on the presence of defects and classify the samples according to how they fit the ideal situation, also providing an exhaustive description of the product. This work can be very helpful for other Regulatory Councils and certification bodies looking for more detailed and demanding methods to assure the sensory quality of the PDO products. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Traditionally, sensory quality control in the food industry has been focused on simple acceptation/rejection methods or on checking if the characteristics of the product are between the pre-established limits (Muñoz, Civille, & Carr, 1992) but in this approach excellence was rarely the issue (Lawless & Heymann, 1998). Despite this, some methods categorising the sensory quality of some products have been reported: cactus pears in syrup (Cerezal & Duarte, 2004), virgin olive oil (International Olive Oil Council, 2007), table olives (International Olive Oil Council, 2008) and some sea foods by means of Quality Index Method (Baixas-Nogueras, Bover-Cid, Veciana-Nogués, Nunes, & Vidal-Carou, 2003; Barbosa & Vaz-Pires, 2004; Huidobro, Pastor, & Tejada, 2000; Sveinsdottir, Hyldig, Martinsdottir, Jørgensen, & Kristbergsson, 2003). In the particular case of traditional products, these sensory properties must be related to a region, elaboration procedure or raw materials (Ballester, Dacremont, Le Fur, & Etiévant, 2005; Bertozzi, 1995; Cayot, 2007; Parr, Green, White, & Sherlock, 2007). This is even of especial importance in products commercialised with quality labels (Protected Designation of Origin, Protected Geographical Indication. . .). These products are sold at higher prices than similar products without these labels, and the consumer expects some particular characteristics that justify this ⇑ Corresponding author. Tel.: +34 945013075; fax: +34 945013014. E-mail address: [email protected] (F.J. Pérez Elortondo). 0950-3293/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodqual.2011.03.008

extra-price. So, sensory properties of these products should differentiate them and it is necessary to prove a difference of quality between non-certified and certified products (Bertozzi & Panari, 1993; Cayot, 2007). In this sense, it seems obvious that the sensory quality control of products with quality labels must be stricter than in conventional products. In the case of PDO wines, the Official Journal of the European Union (Official Journal of the European Union, 2008) establishes that, when registering the product, its analytical and sensory characteristics must be specified, although without detailing more. In fact, majority of the PDOs include very generic mentions to sensory properties, usually referring to ‘‘characteristic properties’’ but without indicating them. In addition to this lack of detail, in many cases trained panels are not approached, and the evaluation relies on the so called ‘‘expert tasters’’ (Feria-Morales, 2002) or on a small group of experienced people but without a specific training and monitoring. Another handicap in the sensory quality evaluation of products with quality labels are the score cards. In fact, it is very frequent to use generic cards, which contradicts the fact of having these products special characteristics determining the quality. These cards present some limitations: - Usually parameters are not specified enough (i.e. what are we referring to if we score the balance in a wine? And what about the harmony? The concept underlying these terms are the same for all the assessors?).

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- Often, the criteria to score each parameter are not defined enough, so it can be very influenced by the opinion, formation and experience of each assessor. - The range of wines considered in many score cards is too wide (‘‘still wines’’, ‘‘sparkling wines’’. . .) so the specificities of particular wines are not considered. Even, in many cases the same card is used for red and white wines. So, it is necessary to develop methods to evaluate in a comprehensive manner the sensory quality of these specific products, considering their particular characteristics. Also, the categorisation of the quality of wines without defects must be approached to make possible to differentiate among correct products. It would help to improve the quality control and also to stimulate the producers to try fitting the high quality standards. There are some reports of methods developed in this direction, which compare the product analysed with the ideal one, providing detailed information about the strong and weak points of the product: methods for Specific Designation Asparagus from Navarra (Torre, 2002), PDO Idiazabal cheese (Pérez Elortondo et al., 2007) or young red wine from Rioja Alavesa (Etaio et al., 2010). There is also a guide to define the procedure to assess the sensory quality of oils applying to use a PDO (International Olive Oil Council, 2005). Some of these methods consider the citation frequency of defects by the experts, although the consideration of citation of positive attributes is very infrequent. Txakoli wine from Bizkaia is a traditional product made in the Basque province of Bizkaia for many centuries, especially from the XVI century (Corcuera & González, 2007). In this region the climate is Atlantic and vineyards are placed lower than 400 m over the sea level. The PDO Bizkaiko txakolina – txakoli de Bizkaia was created in 1994 to protect and promote it. Nowadays 55 wineries are included in the PDO, with a total production of 1,240,118 l in 2009 (data from the Regulatory Council: http://www.bizkaikotxakolina. org/index.php?idioma=es&seccion=1&ctipo=2&contenido=429). As established in the regulations (EHAA/BOPV (Euskal Herriko Agintaritzaren Aldizkaria/Boletín Oficial del País Vasco), 2008), the minimum alcoholic content must be 10% (v/v). These wines can be rosé, red, white wine fermented in oak barrel or sparkling wine, but the 85–90% of the production is un-oaked white wine. The main and recommended grape varieties are Ondarrabi zuri and Ondarrabi beltza (Vitis vinifera L), although the use of other grape varieties (Ondarrabi zuri zerratia/Petit Courbu, Mune mahatsa/Folle Blanche, Izkiriota handia/Gros Manseng, Izkiriota ttippia/Petit Manseng, Sauvignon blanc, Riesling, Chardonnay) is permitted, but with some restrictions. There are several publications about txakoli from Bizkaia but scientific reports describing it have not been published. The expressions more widely used to describe white txakoli are fruity odours, ‘‘fresh’’ and slightly acid, with little natural bubbles and with pale yellow hue with greenish reflects (Corcuera & González, 2007). Regarding the sensory quality control used to qualify these wines, it is based on the previous OIV card for international championships (Organisation Internationale de la vigne et du vin, 1994). Six parameters are evaluated (visual phase, odour intensity, odour quality, flavour intensity, flavour quality, harmony) by an expert panel and scoring increases as quality decreases. When the score exceeds a predetermined punctuation the wine is not qualified. A list with 12 possible causes of disqualification is also provided with the card to the assessors. Quality control of the wines is done in two different ways: wines from tanks to qualify the batch (not filtered) and wines bottled for commercialisation (control made some months after batch qualification, in order to check that the wine maintains the quality). Although the assessors are people with years of experience, the method is too general and does not consider specifically the partic-

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ular characteristics of these wines when analysing their sensory quality. In this sense, the Regulatory Council of the PDO Bizkaiko txakolina – txakoli de Bizkaia was interested in improving the qualification of the wines looking for a more detailed and specific method. The aim of the present work is to describe the procedure used to develop the new method for white txakoli wines. It can be very useful for other PDOs and laboratories looking for improving the quality control for specific food products, and also when it is defined for the first time. 2. Materials and methods 2.1. Participants Seventeen discussion sessions of 2–2 h and half were held with the participation of 13 experts. Participants were oenologists (4), winemakers (5), agronomy technicians (1) and sommeliers (3) with deep knowledge about txakoli wines. Seven of them were also members of the panel that evaluated at that moment the txakolis for qualification. The participation of different type of experts is expressly stated in French regulations (INAO-DIR-2008-02 rev2) when product representativeness is considered. As reported by Bende and Nordin (1997), experts know how to describe the sensations in words better than consumers. The higher precision and accuracy of expert’s vocabulary allow effective communication among them (Chollet & Valentin, 2000; Hughson & Boakes, 2001). Also, the judgments of typicality and representativeness of wines is often assessed by experts (Moio, Schlich, Issanchou, Etiévant, & Feuillat, 1993; Parr et al., 2007; Sauvageot, 1994), who also master the technical aspects of winemaking and the impact of chemical composition on wine taste (Ballester et al., 2005). 2.2. Wines Sixty-two Bizkaiko txakoli wines from different wineries were evaluated throughout the discussion sessions, covering the range from defective wines to very high quality wines. Some of the samples were taken directly from tanks and other samples were already bottled for commercialisation. 2.3. Sample preparation and evaluation Wine evaluation was done in the tasting room of the Regulatory Council. Wines selected for each session were coded with three digits and placed laid down in a cellar at 9 °C (the experts agreed that the optimum temperature to serve them would be 9–10 °C). Wines were opened and immediately served to be evaluated. The volume used was 35 ± 4 mL, measured with a volumetric pourer. In order to avoid the possible colour bias reported by some authors (Morrot, Brochet, & Dubourdieu, 2001; Parr, White, & Heatherbell, 2003; Tromp & Van Wyk, 1977) it was decided to carry out odour and ‘‘in mouth’’ evaluation in black glasses before appearance evaluation. Water and unsalted crackers were provided to the assessors to eliminate residual sensations between samples. The number of samples evaluated at each session ranged from 2 to 12, depending on the content and the objectives of each session. When samples were evaluated and commented at the same time all the participants assessed them in the same order, whereas random presentation was used when a higher number of samples were evaluated without discussion. Scores and comments were annotated in cards corresponding to each development phase, until the establishment of the definitive score card.

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2.4. Steps to develop the method

3. Results and discussion

Method was developed throughout several consecutive steps, although some of them were carried out simultaneously. Main steps were the following:

3.1. Parameters to evaluate and scoring criteria

- Attribute generation: Terms of odour, aroma, taste and mouthfeel, and appearance were sorted by wine pair comparison initially, and by simple description of each sample in subsequent sessions. - Selection of the parameters defining the quality: On the basis of the attribute discussion, the parameters that determine the sensory quality of the wines were chosen, considering the citation frequency, the parameters usually reported in the bibliography and the opinions of the experts. Two main questions were asked to dynamize the discussion: ‘‘Does this parameter really influence the sensory quality of the wine?’’ and ‘‘Does this parameter differentiate among wines?’’. - Definition of the ‘‘ideal situation’’, quality grading and scoring criteria for each parameter: a discontinuous scale of 5 points to score each parameter was agreed among the experts. The ideal quality situation (very high quality – score 5) was defined by answering this question: ‘‘What are the characteristics that a txakoli wine from Bizkaia must present to be considered the ideal one?’’. To answer this question the consideration of its characteristic properties played a very important role. Next, the situations related to scores 4 (high quality), 3 (medium quality) 2 (low quality) and 1 (very low quality) were discussed. Definition of sensory situations was done by a deep discussion, looking for the minimum where all, or the majority of the experts, agreed. Situations were characterised by the presence/absence of concrete attributes in some cases and by the perceived intensity in other cases. Thus, by detailing the scoring criteria, the influence of opinions, likings or formation of each assessor is minimised. To make easier understanding the criteria decision trees were developed. - Definition of the evaluation methodology: it was done by consensus among the experts with the aim of homogenising the tasting procedure, so all the assessors evaluate in the same manner and using the same techniques. Evaluation procedure was tried to be exhaustive but as simple as possible. - Definition of the score card: After defining the parameters, the scales, the most common attributes and defects, and the order to evaluate the parameters, the definitive score card was developed. - Definition of the contribution of each parameter to the overall sensory quality: on the basis that the different parameters do not have the same importance, the weight of each of them on the global quality (expressed as %) was defined by discussion with the experts. - Development of sensory references: references were used to homogenise the sensory concepts among the participants and to be used in the subsequent panel trainings.

Based on the terms collected in the first sessions, and also considering the parameters usually cited in the bibliography and those included in the wine score cards, the seven parameters determining the sensory quality of txakoli wines from Bizkaia were defined: odour intensity and complexity (by orthonasal way), aroma intensity and complexity (by retronasal way), balance and body, global persistence, and appearance. Definition of each parameter is shown in Table 1. Although txakoli is not characterised as a wine with intense odour, it was considered interesting to include this parameter because txakoli wines with more intensity present higher quality than those with weak intensity. The score is given by comparison of the odour intensity of the sample with a medium intensity reference prepared in the laboratory. Odour intensity is a parameter usually included in score cards. In some of them it is indicated expressly ‘‘positive intensity’’ (score card for international competitions of the Organisation Internationale de la vigne et du vin, OIV, and the Union Internationale des Oenologues, UIO, 2009) or differentiated without defects-odour intensity and defective odour intensity (score card of the Faculté d’oenologie de Bordeaux, reproduced in Peynaud & Blouin, 2002). After considering the possibility of off-odour contributing to the odour intensity, it was agreed by the experts that it does not make sense to give a quality score related to the odour intensity if a defect is present. So, if any defect was perceived when smelling the wine the score would be directly 1 or 2 in the 5-points scale, depending on the importance of the defect (Fig. 1). In addition, the mention to ‘‘atypical attributes’’ was included together with defects. They refers to odours that, although can be pleasant and positive in other wines, are totally foreign in txakoli wines from Bizkaia. Regarding odour complexity, a very deep discussion was held to define the optimum situation. Typicality concept [as a concept supported by the existence of a common memorised prototype which represents the image of all the previous experiences of wines from the type (Casabianca et al., 2005)] was excluded. The main reason was that in the past, due to the lack of optimum techniques to make and keep the wines, txakoli was associated to wines excessively acid (quite often by pricking) and not odour complex. So, the key odour attributes desirable in actual txakoli are mainly related to the recommended grape varieties (Ondarrabi zuri and Ondarrabi beltza) but also opened to the sensory characteristics provided by the minority grape varieties accepted. Thus, experts agreed that the attributes defining the odour complexity are white fruit, citric and herbaceous. However, as different situations can be differentiated within these families, it was decided to split them into ‘‘appropriate’’ situations (key attributes) and ‘‘not totally appropriate’’ situations (non-key attributes). Table 2 shows the description of the situations for these tree families and the list of the other frequent attributes and the most frequent defects.

Table 1 Parameters that determine the sensory quality of White txakoli wine from Bizkaia and weighting of each one in the global quality. Parameter

Definition

Weighting in the global quality

Odour intensity Odour complexity Aroma intensity Aroma complexity Balance and body

Global intensity of odour* Number and type of odours (or odour families) Global intensity of aroma* Number and type of aromas (or aroma families) Balance: situation where there are not taste or mouth-feel sensations outstanding by excess or lack. Body: global intensity of taste and mouth-feel sensations. ‘‘Volume’’ in mouth. Length of aromas remaining after spiting out the wine (taste and mouth-feel sensations are only considered if defective)* Whole of characteristics perceived by the eyesight.

10 20 5 20 25

Global persistence Appearance *

Intensity/persistence of defects does not contribute to this parameter, and also decreases the quality score.

15 5

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Fig. 1. Decision tree for odour/aroma intensity.

Odour complexity is considered in all already available wine score cards, although the denominations used change among cards: ‘‘aroma notes’’ (score card of the Unión Española de Catadores, reproduced in Del Castillo, 2005), ‘‘aroma quality’’ [score card of the Faculté d’oenologie de Bordeaux, hedonic wine tasting sheet for quality assessment of Jackson (2000)], ‘‘nose quality’’ (score card for international competitions of the OIV and UIO). However, the criteria to give the score are not usually described; there is not a direct link between the particular attributes perceived and the score. In this sense, the proposed decision tree (Fig. 2) establishes the score on the basis of predefined situations, avoiding personal considerations. With regard to the aromas, it was considered that aroma complexity would have similar importance to odour complexity. However, aroma intensity would have lower importance than odour intensity because there are more sensations (tastes and mouth-feel sensations) affecting the overall intensity impression. These are parameters that are not usually expressly considered in the different score cards. In some cards aromas are considered together with taste and mouth-feel sensations into the ‘‘flavour’’ (hedonic wine tasting sheet for quality assessment of Jackson) or into the ‘‘taste’’ parameters (score card for international competitions of the OIV and UIO), whereas other cards do not consider the aroma evaluation in mouth (score card of the Unión Española de Catadores, score card of the Faculté d’oenologie de Bordeaux). In the case of the card used by the panel of PDO Bizkaiko txakolina

Fig. 2. Decision tree for odour/aroma complexity.

aroma characteristics are included together with the other sensations perceived in mouth, scored as flavour intensity and flavour quality. So, aroma attributes are not collected. After an exhaustive discussion about the situation of balance among taste and mouth feel sensations, it was decided to include ‘‘balance’’ as one of the parameters to evaluate. Thus, a theoretical definition of the desirable situation was formulated: acidity must not be excessive or insufficient; bitterness must not be excessive although it is acceptable not to be perceived; sweetness must not be excessive although it is acceptable not to be perceived; alcoholic/burning sensation must not be excessive. To define what if ‘‘excessive’’ sensory references were developed and discussed. When scoring the balance the presence of these imbalance causes is considered, decreasing the score from 5 according to the number of imbalance causes and their importance. The assessors must indicate the imbalance causes that explain the given score. The discussion about the body consideration intertwined with discussion about balance, because some imbalance causes are closely related to not enough body. At the same time, all the experts shared that the importance of body is much lower that balance. So,

Table 2 Attributes and defects of odour/aroma considered when evaluating the wines. Key attributes

Non-key attributes

Defects

White fruit appropriate (ripe apple/pear with ‘‘fresh’’ and slightly acid sensation)

White fruit not totally appropriate (over-ripe apple/pear)

Dampness Oxidised Sulphurous

Citric appropriate (ripe citric fruit)

Citric not totally appropriate (over-ripe citric fruit)

Acetic Glue Chemical

Herbaceous appropriate (aromatic herbs [fennel, sage, salvia, green aniseed, . . .], apart from the possible presence of fresh grass)

Herbaceous not totally appropriate (fresh grass. . . but without aromatic herbs. Do not confuse this attribute with fermented grass, silo. . . which are defects).

Burnt rubber Rotten eggs/onion peel Others (indicate)

Tropical fruit Floral Lactic Bakery Others (indicate)

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Fig. 4. Decision tree for global persistence. Fig. 3. Decision tree for balance and body.

to consider this possibility of not enough body it was decide to incorporate to the balance parameter, allowing decreasing one point in the score when body was not enough (Fig. 3). Balance as equilibrium situation among tastes and mouth-feel sensations is included in some score cards (score card of the Unión Española de Catadores, score card of the Faculté d’oenologie de Bordeaux) but in other cards it is not included (hedonic wine tasting sheet for quality assessment of Jackson, Davis 20-point scale [Amerine & Roessler, 1983; Ough & Baker, 1961]) or it is considered into more complex parameters where the criteria about how the possible imbalance situations affects the score is not explained (score card for international competitions of the OIV and UIO). Anyway, although having balance included in the card, it is necessary to define how is the balance situation in each type of wine, because the optimum intensities and combinations of acidity, bitterness, sweetness and other mouth-feel sensations are not the same for all the white wines. In the case of the card used by the panel of Bizkaiko txakolina wine there is not a balance consideration, which is supposed to be measured together with other characteristics into ‘‘quality of taste’’ parameter. Body parameter is included expressly in several score cards (score card of the Unión Española de Catadores, Davis 20-point scale) and in other cards this concept would be considered under other related denominations: structure (score card of the Faculté d’oenologie de Bordeaux), flavour intensity (hedonic wine tasting sheet for quality assessment of Jackson). In the previous card used for Bizkaiko txakolina body is not included, and it would be considered into the undefined parameter called ‘‘taste intensity’’. Regarding the sensations remaining once the wine has been spitted out, experts agreed that the sensations determining the quality would be the aromas and the time that they persist. Despite this, if any aromatic defect or imbalance cause is perceived when the wine is not already in the mouth, the quality score would be determined by it, and not by the aromatic persistence. So, as it can be seen in Fig. 4, the possible presence of these negative situations is considered firstly and then the persistence of the aromas. A positive aromatic persistence longer than 5 s is considered as the optimum situation. Although it is not included in some score cards (Davis 20-point scale, score card of the Faculté d’oenologie de Bordeaux), persistence is a parameter usually considered when evaluating wine quality. Nevertheless, besides not specifying in some cases the length of the persistence related to each score, it is not clearly explained how to score when a defect is perceived (score card for international competitions of the OIV and UIO, score card of the Unión Española de Catadores, hedonic wine tasting sheet for

quality assessment of Jackson). In the case of the card used for the txakoli panel persistence was not included, so this information was not collected. For visual characteristics experts’ opinion was that they were not very important but there are some situations that are defective or diminish the quality, so this parameter was also included in the method. Several concepts contributing to the visual characteristics were cited by assessors and discussed (cloudiness, hue, colour intensity, bubbles, bitartrate crystals. . .) but, instead of evaluating each one individually, it was decided to consider all of them in a multidimensional concept called ‘‘appearance’’. Experts agreed that the optimum situation for Bizkaiko txakolina wine lies in a limpid (not cloudy at all) appearance with a green to straw-yellow hue without being too much pale, without crystals and without many or too big bubbles. From this point, the possible situations and the related scores were defined. Some of them were considered defective (scores 1–3) and situations not defective but diminishing quality were also defined and linked to score 4. Decision tree is shown in Fig. 5. As can be seen in Table 3 the criteria for appearance scoring change between bottled wines (checked some months after batch qualification to check the quality maintenance) and wines taken directly from the tanks (without the definitive filtering before bottling), with a less strict requirements for the second ones. Appearance is the unique parameter with a double criterion. Visual characteristics are always present in the score cards although they are usually decomposed in two or more of the concepts cited above: ‘‘limpidity’’ and ‘‘aspect other than limpidity’’ (score card for international competitions of the OIV and UIO), ‘‘colour intensity’’ and ‘‘colour hue’’ (score card of the Faculté d’oenologie de Bordeaux), ‘‘limpidity’’, ‘‘colour intensity’’ and ‘‘colour hue’’ (score card of the Unión Española de Catadores), ‘‘appearance’’ and ‘‘colour’’ (Davis 20-point scale). Anyway, criteria to give a score to some of these parameters are often not specified enough.

Fig. 5. Decision tree for appearance.

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I. Etaio et al. / Food Quality and Preference 23 (2012) 138–147 Table 3 Defective and quality diminishing situations of appearance for bottled txakoli and for txakoli from tank. Defective situations

Quality diminishing situations (but no defects)

Important

Slight

Very slight

Bottled txakoli

- Quite/very cloudy - Obvious rosé hue

-

Slightly cloudy Quite a lot bitartrate sediments Very inadequate burbles Very slight rosé hue

-

Some bitartrate sediments Inadequate burbles Very pale Very goldy hue

- Slightly pale - Slight goldy hue

Txakoli from tank

- Very cloudy - Obvious rosé hue

-

Quite cloudy A lot of bitartrate sediments Very inadequate burbles Very slight rosé hue

-

Slightly cloudy Quite a lot bitartrate sediments Inadequate burbles Very pale Very goldy hue

-

Very slightly cloudy Some bitartrate sediments Slightly pale Slight goldy hue

Fig. 6. Methodology to evaluate the sensory quality of white txakoli from Bizkaia.

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Fig. 8. Example of a result report (page 1).

The six parameters corresponding to ‘‘by nose’’ and ‘‘in mouth’’ evaluation must be evaluated firstly using black glasses. Later, appearance of all the samples is evaluated in transparent glasses under an illumination very similar to daylight. Previously to wine sample evaluation reference of odour and aroma intensity must be evaluated to score these two parameters by comparison with the reference. References of odours and imbalance causes are also presented to the assessors each several sessions. Score card is shown in Fig. 7. In addition to the scale for each parameter a list with the most frequent attributes and defects is included for odour and aroma complexity. The list of imbalance causes for balance-body, aroma defects and imbalance causes for global persistence, and defects and quality diminishing causes for appearance are included in the card too. The possibility of citing other attributes or defects in any parameter is also considered by the ‘‘others’’ box. In this manner, each assessor must indicate the situations that explain each score. 3.3. Contribution of each parameter to the global quality, data treatment and analysis report

Fig. 7. Score card to evaluate the sensory quality of white txakoli from Bizkaia.

3.2. Evaluation procedure and score card The procedure to evaluate each of the parameters and the evaluation order was defined by consensus with the experts and, together with the decision trees, was detailed in an evaluation handbook which was provided to each assessor. The procedure summarised is shown in Fig. 6.

The weight of each parameter to the global quality of the wine was defined by consensus. Odour parameters, ‘‘in-mouth’’ parameters and appearance represent 30%, 65% and 5% of the quality, respectively. Parameters with a higher contribution to the quality are balance-body, odour complexity and aroma complexity, whereas aroma intensity and appearance are the least important ones (Table 1). The defined percentages are quite similar to the reported by Etaio et al. (2010) in the method for young red wines from Rioja Alavesa, although for txakoli wines odour and aroma complexity gain importance at odour and aroma’s expense, appearance becomes less important (in white wines colour is usually less relevant than in red wines) and persistence’s weight increases. Weighting of importance of the different parameters to calculate the global score has been reported in sensory quality evaluation of asparagus with specific designation Navarra (Torre, 2002) and cactus pears (Cerezal & Duarte, 2004). Regarding data treatment, once the data from the seven participants who take part in each quality control session are collected, the score mean for each parameter is calculated. If any value is out from the range defined by the panel mean ±1.5 units, it is

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Fig. 9. Example of a result report (following pages).

removed and the mean is recalculated with the remaining data. In the report for the winery the score mean of each parameter and the

global quality score of the wine (by applying the cited percentages) are included. In this way, the winemaker can know exhaustively

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where the wine quality comes from, the weak and the strong points of his/her wine. With respect to the scores needed to reach the qualification it was a matter not defined in the discussion sessions with the experts, because this is a decision to take by the Regulatory Council. Anyway, in a method as the explained in this work it seems natural to establish a minimum score for global quality and also a minimum score for each parameter (or at least for the most important ones). Also, with this kind of method it is possible to categorise qualified wines by establishing additional high quality standards, in order to distinguish those products that fit better the defined pattern. Citation frequency of attributes, defects and imbalance causes is considered too and included in the report as percentage of assessors indicating them, shown as bar charts. Also when 2/3 of the assessors cite an attribute, defect or imbalance cause, it is considered that is present in the wine and it is expressly pointed out in the report. If for a particular attribute (for example citric odour) citation frequency of 2/3 is not reached as ‘‘appropriate situation’’ (for example 3 citations over 7 assessors) or as ‘‘not totally appropriate situation’’ (for example 3 citations over these 7 assessors), but the sum of both frequencies reach the 2/3 (6/7 in the example), then the ‘‘not totally appropriate’’ situation is marked in the report as present in the sample. The explanation is that, although the appropriateness of the attribute remains unclear, it is obvious that it is present in the sample and must be noticed. Information about citation frequency is of great value for winemakers because they can know the particular characteristics of the wine, which explain the scores of the different parameters. Figs. 8 and 9 show an example of a result report.

3.4. Sensory references The composition and preparation procedure of the sensory references developed for the different attributes, defects and imbalance causes are shown in Table 4. Majority of the references were prepared in a wine base in order to get the sensations elicited by each reference as close as possible to the perception of this sensation when evaluating the wine. Wine base is composed by a very homogeneous commercial white wine (Don Simón, Bodegas García Carrión) diluted with water until 75% of wine, and then added 2 mL of absolute ethanol per 100 mL. Due to the very small quantities of chemical substances needed some odour references were prepared from concentrated solutions. Initially, several references for each attribute/defect made with different compounds were presented. Once the most suitable substance(s) were chosen, intensity and proportions of the different substances included in each reference were adjusted by successive discussions and re-formulations. It extended over 12 of the sessions held to develop the method, mainly because it was difficult to reach a consensus about the appropriateness of some references (white apple, herbaceous, dampness, chemical and bakery). All the discussions were carried out with references previously frozen and defrosted, so that freezing could be used in the future to make easier the reference management. 4. Conclusions This article describes the work developed to improve the sensory evaluation method for qualification of txakoli wine from

Table 4 Composition and preparation procedure of references for odour and imbalance causes. Attribute

Concentrated solution (CS)

Reference preparation

Odour/aroma intensity*

Butyl acetate at 1% v/v and ethyl valerate at 1% v/v in a solution water – absolute ethanol (1:1) Ethyl butyrate at 1% v/v in a solution water – absolute ethanol (1:1) Butyl acetate at 1% v/v in a solution water – absolute ethanol (1:1) Ethyl valerate at 1% v/v in a solution water – absolute ethanol (1:1) Limonene at 1% v/v in a solution water – absolute ethanol (1:1) Cis-3-hexen-1-ol at 1% v/v in a solution water – absolute ethanol (1:1)

60 lL of CS in a final volumen of 100 mL of white table wine

White fruit appropriate

Citric appropriate Herbaceous appropriate Tropical fruit Floral Lactic Dampness

Linalool at 1% v/v and geraniol at 1% v/v in a solution water – absolute ethanol (1:1) Diacetyl at 1% v/v in a solution water – absolute ethanol (1:1) Metoxipropil pyrazine at 5% in a solution water – absolute ethanol (1:1) 2-methylisoborneol at 1 ppm in a solution water – absolute ethanol (1:1)

Oxidised Sulphurous Acetic Glue Chemical Burnt rubber Rotten eggs/onion peel

Ethanethiol at 0.25% in distilled water. Keept frozen.

Bakery Acidity excess** Sweetness excess** Bitterness excess** Burning sensation excess** WB, wine base. * Reference intensity corresponds with score 3 of the scale (see Fig. 1). ** References correspond with ‘‘important imbalance cause’’ (see Fig. 3).

150 lL of CS of Ethyl butyrate + 75 lL of CS of butyl acetate + 100 lL of CS of ethyl valerate in a final volume of 50 mL of WB

150 lL of CS in a final volume of 50 mL of WB Maceration of 0,1 g of green aniseed in 50 mL of WB 5 min. Filtering and addition of 20 lL of CS. 4 mL of pinneaple juice freshly squeezed in a final volume of 50 mL of WB 15 lL of CS in a final volume of 50 mL of WB 200 lL of CS in a final volume of 50 mL of WB 6 lL of CS of Metoxipropil pyrazine + 15 lL of CS of 2-methylisoborneol in a final volume of 50 mL of WB

100 mL of white table wine maintained 2 weeks in a 500 mL bottle (closed) at 20 °C. 0.03 g of potassium metabisulphite in 50 mL of WB 0.6 mL of acetic acid in 50 mL of WB 15 lL of ethyl acetate in 50 mL of WB 10 mg of o-cresol in 50 mL of WB Solution obtained after burning during 20–30 s 5 g of bike inner tube cut into pieces, macerating them in 60 mL of WB during 5 min and filtering. 200 lL of CS in a final volume of 50 mL of WB – 1.8 g of tartaric acid in 400 mL of white table wine 6 g of sucrose in 400 mL of white table wine 0.010 g of quinine sulphate in 400 mL of white table wine 22 mL of absolute ethanol in 400 mL of white table wine

I. Etaio et al. / Food Quality and Preference 23 (2012) 138–147

Bizkaia. This work faces the frequent situation of PDO products whose sensory quality is evaluated by using generic methods and score cards. The steps for method development described in this work emphasise the particular characteristics associated to the product, so its quality can be assessed in a way more fitted to its original concept. This approach can be very useful for other PDOs looking for improving their quality control methods. In order to focus properly the discussion about the particular characteristics that the product must present it is essential the participation of a sufficient group of experts with a great knowledge about the product and the sector. The use of decision trees that link sensory situations to quality scores represents a very interesting tool to homogenise the criteria used by the assessors and to objectivise the scoring. The need to indicate the sensory situations to justify the scores, besides reducing the subjectivity when scoring, provides detailed descriptive information about each product. These data can be very valuable not only to know the reasons of the disqualification of a product but also to know the aspects that need to be improved to increase its quality. Acknowledgments The authors want to thank the collaboration of the experts who took part in the discussion sessions to develop the method, the Regulatory Council of PDO txakoli de Bizkaia – Bizkaiko txakolina, and also the Ingurumen, Lurralde Plangintza, Nekazaritza eta Arrantza Saila/Departamento de Medio Ambiente, Planificación Territorial, Agricultura y Pesca (Department of Environment, Territorial planning, Agriculture and Fishing) of the Gobierno Vasco – Eusko Jaurlaritza (Basque Government) for funding this work. References Amerine, M. R., & Roessler, E. B. (1983). Wines, their sensory evaluation (2nd ed.). San Francisco (USA): W.H. Freeman. Baixas-Nogueras, S., Bover-Cid, S., Veciana-Nogués, T., Nunes, M. L., & Vidal-Carou, M. C. (2003). Development of a Quality Index Method to evaluate freshness in Mediterranean hake (Merluccius merluccius). Journal of Food Science, 68(3), 1067–1071. Ballester, J., Dacremont, C., Le Fur, Y., & Etiévant, P. (2005). The role of olfaction in the elaboration and use of the Chardonnay wine concept. Food Quality and Preference, 16(4), 351–359. Barbosa, A., & Vaz-Pires, P. (2004). Quality Index Method (QIM): Development of a sensorial scheme for common octopus (Octopus vulgaris). Food Control, 15(3), 161–168. Bende, M., & Nordin, S. (1997). Perceptual learning of olfaction: Professional wine tasters versus controls. Physiology and Behaviour, 62(5), 1065–1070. Bertozzi, L. (1995). Designation of origin: Quality and specification. Food Quality and Preference, 6(3), 143–147. Bertozzi, L., & Panari, G. (1993). Cheeses with appellation d’Origine Contrôlée (AOC): Factors that affect quality. International Dairy Journal, 3(4–6), 297–312. Casabianca, F., Sylvander, B., Nöel, Y., Béranger, C., Coulon, J. B., & Roncin, F. (2005). Terroir et typicité: Deux concepts-clés des appellations d’Origine contrôlée–Essai de définitions scientifiques et opérationnelles. In Proceedings of the international symposium ‘‘Territoires et Enjeux du Développement Régional’’. France: Lyon. p. 22. Cayot, N. (2007). Sensory quality of traditional foods. Food Chemistry, 101(1), 154–162. Cerezal, P., & Duarte, G. (2004). Influencia sensorial de aditivos químicos en tunas (Opuntia ficus-indica (L.) Miller) peladas en almíbar conservada por métodos combinados. Journal of Professional Association for Cactus Development, 6, 102–119. Chollet, S., & Valentin, D. (2000). Le degré d’expertise a-t-il une influence sur la perception olfactive? Quelques éléments de réponse dans le domaine du vin. L’Année Psychologique, 100, 11–36. Corcuera, M., & González, M. (2007). Chacolí. Txakolina (1st ed.). Donostia-San Sebastián: Editorial Nerea, S.A. International Olive Oil Council (2008). Method. Sensory analysis of table olives. COI/ OT/MO/Doc. No 1. Madrid: IOOC. Available from www.internationaloliveoil.org/ downloads/quimica/MET-OT-org-eng.pdf Accessed November 2010. Del Castillo, F. (2005). Organización de la cata y vocabulario específico del catador de vinos. In J. Casal del Rey (Ed.), Análisis sensorial y cata de los vinos de España (pp. 152–177). Madrid: Editorial Agrícola Española.

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