ORIGINAL RESEARCH Changes in sensory quality characteristics of coffee during storage Michaela T. L. Kreuml, Dorota Majchrzak, Bettina Ploederl & Juergen Koenig Department of Nutritional Sciences, University of Vienna, Althanstraße 14, Vienna 1090, Austria

Keywords Abstract Coffee, quantitative descriptive analysis, sensory changes, storage How long can roasted coffee beans be stored, without reducing the typical cof- fee flavor which is mainly responsible for consumers’ enjoyment? In Austria, Correspondence most coffee packages have a best-before date between 12 and 24 months, but it Dorota Majchrzak, Department of Nutritional is not regulated by law. Therefore, there is the need to evaluate changes in sen- Sciences, University of Vienna, Althanstraße sory qualities of coffee beverages prepared from stored coffee beans. For prepa- 14, Vienna 1090, Austria. ration of the coffee beverages, the paper filter method was used. In the Tel: +43-1-4277-54948; Fax: +43-1-4277-9549; quantitative descriptive analysis (QDA) 10 trained assessors evaluated the inten- E-mail: [email protected] sity of 30 coffee attributes after roasting at the 9th and 18th month of storage, respectively. The sensory evaluation results showed reduction in the sensory Funding Information qualities of coffee beverages after 9 months storage of roasted coffee beans. The Funded by Department of Nutritional positive associated odor and flavor attributes decreased in their intensity, Sciences, University of Vienna. whereas the negative associated odor and flavor attributes increased significantly (P < 0.05). After 18 months of storage, the rancid odor and flavor which indi- Received: 16 January 2013; Revised: 13 cate oxidation processes were even considerably perceivable. Consequently, we March 2013; Accepted: 20 March 2013 can assume that changes in sensory quality characteristics of roasted and Food Science & Nutrition 2013; 1(4): 267– vacuum-packed coffee beans during storage are possible. 272 doi: 10.1002/fsn3.35

Introduction et al. 2001; Farah et al. 2006). Caffeine, a xanthine deriva- tive may also cause a characteristic bitter taste depending Coffee is one of the most widely consumed beverages on concentration (Casal et al. 2000; Ky et al. 2001; Farah throughout the world for its unique sensory properties et al. 2006; Keast 2008; Toci et al. 2013). In general, and physiological effects. Studies have shown that there is Robusta coffee is known for a bitter taste and astringency, a great interest on shelf life of roasted and ground coffee while Arabica develops a fine acidity, better flavor, and is (Ross et al. 2006; Manzocco and Lagazio 2009; Makri more intense in overall aroma (Ky et al. 2001; Nebesny et al. 2011; Borem et al. 2013; Toci et al. 2013). Roasting and Budryn 2006). Not only roasting process induces is responsible for the flavor development and is a time- transformation of chemical contents also during storage, temperature-dependent highly complex process, whereby roasted beans are susceptible to further chemical and hundreds of chemical reactions and changes occur simul- physical changes that may greatly affect the sensory qual- taneously. These changes include the Maillard and Strec- ity of coffee beverages. Water (moisture), air (oxygen), ker reactions, degradation of polysaccharides, proteins, light, and extraneous odors have the greatest influence on trigonelline, and chlorogenic acids. The chlorogenic acids quality of coffee during storage. Massive odor- and flavor (CGA), a phenolic compound, are known to be responsi- losses are the consequence of the water solubility of essen- ble for astringency, coffee pigmentation, and aroma for- tial oils of coffee and the formation of volatile flavoring mation. Furthermore, thermal degradation during the substances with oxygen (Ross et al. 2006; Makri et al. roasting process of CGA also contributes to bitterness (Ky 2011; Toci et al. 2013).

ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc. This is an open access article under the terms of 267 the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Sensory Changes of Coffee during Storage M. T. L. Kreuml et al.

There are only few studies and data available on sen- Sensory evaluation sory profiling of coffees during storage (Ross et al. 2006; Manzocco and Lagazio 2009; Makri et al. 2011; Borem Sensory evaluation of the investigated coffee beverages et al. 2013; Toci et al. 2013). The authors investigated the was performed by quantitative descriptive analysis (QDA) sensory changes of coffee beverages made out of roasted according to Stone et al. (1974). It was conducted by a and ground coffee during the storage time in different trained panel of 10 assessors (ISO-Standard 8586 2012) periods, but not longer than 12 months. In Austria, most aged 20–35 years with ample experience in sensory evalu- coffee packages have a best-before date between 12 and ation of coffee, recruited from students of the Depart- 24 months, but this is not explicitly regulated by law. ment of Nutritional Sciences, University of Vienna. The Therefore, there is the need to investigate how long training consisted of a theoretical education, exercises in roasted coffee beans can be stored without reducing the general sensory evaluation, and description of sensory typical flavor of coffee beverages, which is mainly respon- attributes of coffee. Additionally, an individual question- sible for the consumers’ enjoyment. naire composed of questions about the eating habits and availability for the study was conducted. The overall cof- Material and Methods fee odor and flavor as well as the attributes brew-like, roasty, fruity/aromatic, and the sweet taste were defined by the consumers as positively associated descriptors, Coffee samples which characterize a good coffee quality. Woody, earthy, Two green coffee samples, 20 kg Arabica from Ethiopia hay like in odor, and flavor as well as bitter taste and growing area Limu and 10 kg Robusta from Vietnam, pro- aftertaste and astringency were defined as negatively asso- vided from the Austrian Coffee Institute (Hofwiesengasse ciated descriptors. The analysis took place at three times 48, 1130 Vienna), were evaluated in this study. The sam- and occurred immediately after roasting, and after 9 and ples were roasted in a shop roaster with a volumetric 18 months of storage, in individual booths at the sensory capacity of 12 kg at 163–165°C, 10 min for Arabica and laboratory of University of Vienna, designed and 13 min for Robusta, respectively, resulting in a medium equipped consistent with ISO-Standard 8589 (2007). The roasting degree (golden-brown color). Temperature varia- term list generated from trained assessors included five tion inside the roaster was monitored using a thermo- primary sensory categories such as appearance, odor meter during the roasting procedure. Due to the large (orthonasal perception), flavor and taste, mouthfeel, and quantity, Arabica coffee was roasted in two loads aftertaste. Every category was described by certain (Table 1). descriptors and the vocabulary list contains 30 attributes Roasted coffee beans were packed under vacuum con- (Table 2). The selection and definition of the descriptors ditions in commercially available packages and stored in were compiled in accordance with the papers by Han- the dark at ambient temperature over a period of Seok et al. (2008), Andueza et al. (2003), Narain et al. 18 months. Freshly roasted, 9 and 18 months stored cof- (2003), and ICO – International Coffee Organization fee beans were ground with a manual coffee grinder (2002). During the quantitative assessment, the assessors (Zassenhaus, Solingen, Germany) and brewed. For prepa- evaluated the intensity of the specified attributes on a ration of coffee beverages the paper filter method was numeral ordinal 10-unit scale with the end values labeled used (Melitta orginal 1 9 4). The coffee brews were per- as imperceptible and very intense. The coffee samples colated from 50 g of each ground-roasted coffee variety were served in a randomized order and evaluated by with a volume of 500 mL water using a filter coffeemaker QDA three times over two sessions, in the morning and (Philips coffee maker HD 7563/20 1000 W). in the afternoon, respectively.

Table 1. Roasting conditions of evaluated coffee species.

Arabica Ethiopia first load Arabica Ethiopia second load Robusta Vietnam

Roasting date 25 March 2009 25 March 2009 25 March 2009 Roasting temperature (°C) Initial Temp.: 79 Initial Temp.: 80 Initial Temp.: 80 Max. Temp.: 165 Max. Temp.: 163 Max. Temp.: 164 Roasting time (min) 10.40 10.54 13.16 Degree of roast Golden brown Golden brown Golden brown Weight green coffee (kg) 10.50 10.54 10.32 Weight after roasting (kg) 8.97 9.17 8.56

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two repetitions, altogether 20 individual measurements. Statistical analysis For all calculations MS Excel 2003 (Microsoft, Redmond, For each tested coffee species at each examination date, the WA) was used. mean value and standard deviation for each investigated For determination of the statistical significance of dif- attribute was calculated from the data of 10 panelists and ferences between the analyzed coffees, the statistical soft- ware SPSS 15.0 (Statistical Package for the Social Table 2. Brewed coffee sensory attributes and their definitions. Sciences, SPSS Inc., Chicago IL) was applied. Primarily, Categories Descriptors Definitions the K-S-Test (Kolomogorov-Smirnov-Test) was used to show if the data were normally distributed (P > 0.05) or Appearance Color The intensity of color not (P < 0.05). Subsequently, normal distributed data Opacity Nontransparent or (cloudiness) cloudy status were analyzed with t-test for independent samples or Oiliness Greasy and coating ANOVA (analysis of variance), and for not normally dis- appearance tributed data the Mann–Whitney test, was applied. Differ- Odor (orthonasal Overall coffee Aromatics associated with ences were regarded as statistically significant at P < 0.05. perception)/flavor odor/flavor common coffee aroma Brew-like Aromatics associated with freshly brewed Results roasted coffee Roasty Aromatics associated with Quantitative descriptive analysis (QDA) freshly roasted coffee beans Fruity/aromatic Lightly sour and sweet The results of QDA demonstrated large significant differ- aromatics associated with ences in the intensity of all evaluated sensory attributes in several fruits both investigated coffee cultivars after storage (Table 3). Burnt/smoky Aromatics associated with burnt rice or something scorched or burnt Impact of storage on the sensory attributes Woody Aromatics associated with of evaluated coffee species wooden materials Earthy Aromatics associated with The coffee brews prepared from freshly roasted Arabica and soil or clay freshly cut grass Robusta beans showed significant (P < 0.05) higher inten- or hay during biting sities in positively associated odor and flavor attributes, Hay-like Aromatics associated with such as overall coffee odor and flavor, brew-like, roasty, (grassy) freshly cut grass or hay and fruity/aromatic as well as the sweet taste than samples during biting Staleness Aromatics associated with brewed from coffee beans stored for 9 and 18 months. Cof- moldy, old coffee fee beverages prepared from the 18 months stored beans Rancid Aromatics associated with indicated the lowest intensities of positive coffee descrip- oxidations processes of fat tors. In contrast, the negative associated odor and flavor Taste Sweet A basic taste associated with attributes like burnt/smoky, woody, earthy, and hay like as sucrose solution well as the astringency, bitter taste, and aftertaste increased Sour A basic taste associated with significantly (P < 0.05) during storage. In addition, stale- citric acid solution Bitter A basic taste associated with ness and rancid odor and flavor, which indicate oxidation caffeine solutions processes, were particularly perceivable after 18 months of Mouthfeel Viscosity Sticky characteristics to palate storage (Table 3). or mucosal surface in the oral cavity Astringent Feelings associated with dry Differences in sensory changes between sensation associated with Arabica and Robusta during storage immature permissions or black/green tea Both coffee varieties, Arabica and Robusta showed signifi- Aftertaste Overall Long-lasting overall impression cant differences in the intensity of all evaluated sensory coffee 1 min after having descriptors at the beginning of investigation and during swallowed the coffee storage. Coffee beverages prepared from Arabica beans beverage demonstrated a significant (P < 0.05) higher intensity of Bitter Long-lasting bitter taste 1 min positive attributes compared to Robusta coffee at each after having swallowed the point of assessment. After 18 months of storage, these coffee beverage positively associated descriptors decreased significantly

ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc. 269 Sensory Changes of Coffee during Storage M. T. L. Kreuml et al.

Table 3. Sensory evaluation (QDA)1 results of brewed coffee prepared with fresh and stored coffee beans (mean Æ SD).2

Arabica2 Robusta2

Stored Stored

Attributes Freshly roasted 9 months 18 monthsFreshly roasted 9 months 18 months

Odor Overall coffee 8.13Aa Æ 0.80 7.10Bb Æ 1.34 5.50Cb Æ 0.76 7.47Ac Æ 1.48 6.22Bd Æ 2.01 4.60De Æ 1.73 Brew-like 7.78Aa Æ 1.24 6.50Bb Æ 1.09 4.25Cc Æ 0.99 5.17Dd Æ 1.82 2.82Ee Æ 1.47 2.10Fe Æ 0.64 Roasty 7.02Aa Æ 1.30 6.06Bb Æ 1.28 4.70Cc Æ 1.77 5.29Dd Æ 1.77 3.29Ee Æ 1.56 2.45Fe Æ 1.15 Fruity/aromatic 7.27Aa Æ 0.99 6.50Bb Æ 1.15 4.30Cc Æ 2.00 1.73Dd Æ 1.43 1.29Ed Æ 1.36 1.10Fd Æ 0.64 Burnt/smoky 1.48Aa Æ 1.36 2.00Ba Æ 1.68 4.50Cb Æ 1.39 6.53Dc Æ 1.45 7.22Ec Æ 1.29 8.20Fd Æ 0.77 Woody 0.78Aa Æ 0.75 2.16Bb Æ 1.22 3.20Cc Æ 1.01 5.40Dd Æ 1.10 7.15Ee Æ 1.63 7.73Fe Æ 0.97 Earthy 0.54Aa Æ 0.56 1.73Bb Æ 1.08 2.85Cc Æ 1.09 5.13Dd Æ 1.15 7.24Ee Æ 1.48 7.63Fe Æ 0.96 Hay-like 1.16Aa Æ 1.16 2.30Bb Æ 1.46 3.40Cc Æ 0.82 5.01Dd Æ 1.08 5.22Ed Æ 0.91 6.55Fe Æ 1.00 Staleness 0.00Aa Æ 0.00 1.81Ab Æ 1.29 4.18Ac Æ 2.34 0.13Ad Æ 0.26 6.46Ae Æ 1.90 7.35Ae Æ 0.73 Rancid 0.00Aa Æ 0.00 1.03Bb Æ 1.16 3.70Cc Æ 0.57 0.00Dd Æ 0.00 4.26Ee Æ 2.66 6.35Fe Æ 0.67 Flavor Overall coffee 8.01Aa Æ 1.00 7.17Ab Æ 1.11 6.40Ac Æ 0.94 6.78Ad Æ 2.08 5.81Ade Æ 2.37 4.00Ae Æ 1.86 Aa Brew-like 7.34 Æ 1.32 6.19Bb Æ 1.61 4.70Cc Æ 1.49 4.15Dd Æ 2.26 2.87Ee Æ 1.71 2.30Fe Æ 1.72 Roasty 7.11Aa Æ 1.41 6.02Bb Æ 1.76 4.90Cc Æ 1.74 4.52Dd Æ 2.33 2.91Ee Æ 1.76 2.25Fe Æ 1.33 Fruity/aromatic 6.90Aa Æ 1.11 6.40Ba Æ 1.77 3.85Cb Æ 1.53 0.94Dc Æ 1.08 0.79Ecd Æ 0.85 0.30Fd Æ 0.44 Burnt/smoky 1.43Aa Æ 0.86 2.36Ba Æ 1.94 4.30Cb Æ 1.22 6.27Dc Æ 1.62 7.11Ecd Æ 2.77 7.75Fd Æ 1.07 Woody 1.05Aa Æ 0.97 2.02Bb Æ 1.16 3.55Cc Æ 1.05 5.81Dd Æ 1.12 7.24Ee Æ 1.58 8.15Fe Æ 0.59 Earthy 0.71Aa Æ 0.74 1.84Bb Æ 1.14 3.70Cc Æ 0.91 5.18Dd Æ 1.24 7.40Ee Æ 1.62 8.15Fe Æ 0.80 Hay-like 1.05Aa Æ 0.85 2.52Bb Æ 1.51 4.15Cc Æ 1.09 4.72Dd Æ 1.19 5.03Ed Æ 1.12 6.65Fe Æ 1.23 Staleness 0.00Aa Æ 0.00 1.88Bb Æ 1.56 4.25Cc Æ 1.80 0.07Ad Æ 0.15 6.91De Æ 1.94 7.30Fe Æ 0.98 Rancid 0.00Aa Æ 0.00 0.92Bb Æ 1.27 1.90Cc Æ 1.17 0.00Ad Æ 0.00 3.47De Æ 2.91 4.55Fe Æ 0.94 Taste Sweet 2.95Aa Æ 1.27 2.75Ba Æ 1.29 1.70Cb Æ 1.02 0.54Dc Æ 0.74 0.48Ec Æ 0.71 0.15Fc Æ 0.37 Sour 3.04Aa Æ 1.60 3.92Ba Æ 2.31 5.00Cb Æ 0.78 2.11Ac Æ 1.94 2.37Dc Æ 1.94 4.35Cd Æ 1.66 Bitter 3.55Aa Æ 1.62 4.14Ba Æ 0.51 6.10Cb Æ 1.11 7.36Dc Æ 0.95 8.39Ed Æ 1.33 8.75Fd Æ 0.47 Appearance Color 6.53Aa Æ 1.78 7.72Bb Æ 1.12 8.45Cb Æ 0.90 7.71Dc Æ 1.97 8.08Bc Æ 1.33 9.03Ed Æ 0,62 Opacity 3.46Aa Æ 2.39 5.26Ab Æ 2.20 6.73Ab Æ 0.91 4.81Ac Æ 2.51 5.76Acd Æ 2.50 6.43Ad Æ 0.99 Oiliness 1.93Aa Æ 1.91 4.07Ab Æ 2.41 4.98Ab Æ 1.81 1.77Ac Æ 1.95 3.34Ad Æ 1.92 4.08Ad Æ 1.17 Mouthfeel Viscosity 3.30Aa Æ 0.80 3.79Ba Æ 1.50 4.75Cb Æ 0.77 3.21Ac Æ 1.45 3.38Bc Æ 1.54 3.60Dc Æ 1.29 Astringent 3.37Aa Æ 2.06 4.11Ba Æ 1.10 5.30Cb Æ 1.38 5.83Dc Æ 1.75 6.22Ec Æ 1.46 7.38Fd Æ 1.06 Aftertaste Overall coffee 6.85Aa Æ 1.82 6.18Bab Æ 1.75 5.55Cb Æ 1.04 6.66Ac Æ 1.83 6.32Bc Æ 1.95 4.40Dd Æ 1.57 Bitter 3.24Aa Æ 1.10 3.68Ba Æ 0.63 5.40Cb Æ 1.14 6.19Dc Æ 1.02 7.38Ed Æ 1.29 8.05Fd Æ 0.83

1QDA, quantitative descriptive analysis: The evaluation of the intensity of the descriptors was done using a 10-unit scale (0 = imperceptible and 10 = very intense). 2Values represent the mean of 20 results Æ SD, standard derivation (10 panelists, 2 repetitions). Capital letters compare Arabica and Robusta treatments, and lowercase letters compare treatments within the variety. Same letters in the same row mean values are not significantly different, whereas different letters in the same row mean values are significantly different.

(P < 0.05) in both coffee cultivars, however, more evident more intense in Robusta than in Arabica the rancid odor in Robusta than in Arabica. The negatively associated and flavor as well as staleness were already noticed after odor and flavor attributes like burnt, woody, earthy, and 9 months and increased significantly (P < 0.05) after hay like, as well as astringency, the bitter taste, and after- 18 months of storage (Table 3). taste were significantly higher (P < 0.05) in the Robusta samples than in the Arabica, even in coffees prepared Discussion from freshly roasted coffee beans. During storage, the negative properties increased significantly (P < 0.05), but Aromatic components are very important in coffee bev- in Robusta beverages more than twice as much than in erages, because they are the principal constituents of sen- Arabica. In samples of both coffee varieties, however sory experience for coffee consumers. Chemical

270 ª 2013 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc. M. T. L. Kreuml et al. Sensory Changes of Coffee during Storage transformation induced by storing roasted coffee beans packed coffee beans are enough to make a great influence are responsible for chemical and physical changes that on sensory coffee cup quality. As time passes by, desirable may have a great influence on sensory quality of coffee positive attributes decreased and the negative ones were brews (Toci et al. 2013). For instance, storage changes in more intensely perceived in both coffee species. Therefore, composition of lipids may contribute to a loss of sensory more restrictive regulations for declaration and limitation quality of coffee beverages. Lipids can be hydrolyzed of the best-before date and the roasting date of coffee are chemically or enzymatically and the rate at which these required. reactions occur depends on environmental and techno- logical aspects, as well as availability of oxygen, moisture, Conclusion temperature, and packaging material (Manzocco and Lagazio 2009). Roasting thermally inactivates hydrolytic The conducted sensory evaluation demonstrated adverse enzymes in coffee beans. Afterwards, moisture and tem- effects on the quality of coffee beverages straight after perature are the main factors, which implement hydroly- 9 months storage of roasted coffee beans. After sis in roasted coffees by affecting the rates of all types of 18 months, the intensity of attributes which indicate oxi- reactions. In addition, the presence of oxygen leads to dation processes increased. Consequently, we can con- the oxidation of unsaturated free fatty acids (FFA), clude that sensory changes are likely during storage of which is responsible for the formation of a huge number roasted and vacuum-packed coffee beans. Therefore, we of volatile compounds, loss of positive attributes such as suggest testing the duration of storage of roasted coffee brew-like, and formation of staleness. Both atmosphere beans by the producers and recommend declaring the and temperature in association with storage time influ- best-before date on the package. enced chemical and sensory changes. The use of inert atmosphere and low temperatures contributed to a Acknowledgments slower degradation of FFA during storage period (Toci et al. 2013). Sour taste, bitterness, and undesired flavor The authors thank Prof. Leopold J. Edelbauer from the notes were recognized as the most important attributes Austrian Coffee Institute for supporting this study by indicating the development of the sensory quality of cof- providing both green coffee cultivars and for establishing fee beverages upon storage (Ross et al. 2006; Manzocco contacts with the coffee roaster. Furthermore great thanks and Lagazio 2009). The sensory evaluation of coffee bev- to all the assessors who attended the sensory tasting at erages from the beans evaluated in our study showed an each assessment point. increase in the intensity of sour taste in Arabica after 18 months of storage and was about 60% higher in Conflict of Interest comparison to coffee beverage prepared from freshly roasted beans. In Robusta coffee, the perceived sourness None declared. doubled at the end of the storage compared to the prep- aration from freshly roasted beans. The bitterness References increased by around 70% in Arabica, while in Robusta Andueza, S., M. 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