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The storage of grape marc: Limiting factor in the quality of the distillate
Food Control 21 (2010) 1545–1549
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The storage of grape marc: Limiting factor in the quality of the distillate Sandra Cortés *, José Manuel Salgado, Noelia Rodríguez, José Manuel Domínguez Department of Chemical Engineering, Sciences Faculty, University of Vigo, Campus Ourense, As Lagoas s/n, 32004 Ourense, Spain Laboratory of Agro-Food Biotechnology, CITI-Tecnólopole, Parque Tecnológico de Galicia, San Cibrao das Viñas, Ourense, Spain
a r t i c l e
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Article history: Received 12 September 2008 Received in revised form 27 March 2010 Accepted 3 April 2010
Keywords: Grape marc Storage system Volatile compounds
a b s t r a c t Grape marc, the mass of skins, stalks and seeds left after the winemaking process, is stored before distillation to produce ethanol by the alcoholic fermentation of the residual sugars. In this work 24 samples of grape marc were stored in four different types of containers. After distillation process, the samples obtained were analyzed by GC–MS to evaluate the influence that the storage exercises on the major volatile composition. Grape marc stored in plastic sacks (1000 kg) produced distillates with low values of the majority volatile compounds, that implies a good quality but a poor aromaticity. Distillates from pomace in plastic drums (250 kg) showed a high content in ethyl esters and higher alcohols, however the concentrations of ethyl acetate and aldehydes and acetal are high too, due to the difficulty to control the aerobic bacteria spoilage. The principal problem of the concrete containers (70,000 kg) is the high methanol production and in the plastic sacks (50 kg) the quick aerobic and anaerobic degradation. With an exhaustive control of oxygen contact, plastic drums and plastic sacks (1000 kg) were the better systems to storage grape marc before distillation. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Orujo is a traditional spirit of Galicia (winegrowing region of NW Spain) obtained by distillation of the vinification sub-products (stalks, skins, pulp and seeds) called grape marc or pomace. As a result, this alcoholic beverage is not only an important source of income for the Galician winegrowing sector, but also a method of making better use of grape residues (pomace), which is also important from the environmental point of view. The production and commercialisation of Orujo in Galicia must be adjusted to the norms reflected in the regulations for the Geographic Denomination of the Aguardientes and Traditional Liquors of Galicia. Other European spirits are produced like Orujos (i.e. Italian Grappas, Greek Tsipouro, French Marc and Portuguese Bagaçeiras). They are similar in terms of raw material, manufacturing techniques and sensorial properties. After pressing the grapes, pomace is stored under anaerobic conditions in order to promote spontaneous alcoholic fermentation of the residual sugars content. Distillation takes place after this alcoholic fermentation, but in some distilleries grape marc is stored during several months before distillation and depending on the storage conditions, methods and systems; the pomace preservation from bacteria and mould is difficult and in the distillate could appear off-flavours (Da Porto, 2002). The bibliographic
* Corresponding author. E-mail address: [email protected] (S. Cortés). 0956-7135/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2010.04.029
references that exist on the characteristics and conditions of this important stage indicate, among others, that the grape marc must be stored in the absence of oxygen, in small containers, and that storage should not be prolonged, although it must be sufficient to complete the alcoholic fermentation while avoiding the proliferation of microorganisms (Cortés, Gil, & Fernández, 2001, 2006; Da Porto, 2002; Usseglio-Tomasset, 1971; Versini & Odello, 1990; Williams & Strauss, 1978). Principally, they are acetic, lactic and butyric bacteria that would cause undesirable secondary fermentations through the formation of a series of volatile compounds with negative aromatic connotations, which notably degrade the sensorial quality of the resulting distillate (De Rosa & Castagner, 1994; Desauziers, Avezac, & Fanlo, 2000; Nykänen, 1986; Silva & Malcata, 1998). Among these compounds should be mentioned: ethyl acetate, the acetic, butyric and propionic acids, 2-butanol and ethyl esters of long-chain fatty acids. The correct selection of storage container for grape marc is one of the most important points of this stage. In general, this selection is directly related to the capacity and production of the distillery or winery and not so much dependent on the characteristics of the container. Medium-to-small producers tend to use small bins and sacks as containers, generally made from plastic. When the winery has a higher production, these methods of storage for grape marc cannot be used, as their installations are not prepared for storing a large number of small containers, nor would it be economically viable. In these cases, the distilleries construct large-capacity containers, called silos, which allow the storage of various tons of grape marc.
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The characteristics of each of the storage containers employed are different, not only in capacity, but also in type of material, design, facility of manipulation, resistance and duration. Therefore, their role with respect to the conservation of the pomace will also be different and it will be necessary to combine production and quality criteria in order to decide which storage system will be the most adequate in each case. Samples of grape marc stored in four different types of containers were used for this study. Following the corresponding distillation process, the major volatile compounds were determined by gas chromatography–mass spectrometry. The object of this study was to determine the chemical composition of the distillates, as a function of the raw-material storage system and to establish the possible significant differences in the mean concentration of each volatile compound, in the different storage systems studied. The results obtained will allow the establishment of a series of criteria for the selection of a storage system that will permit a better quality of the final product, Orujo. 2. Materials and methods 2.1. Samples and containers Grape marc employed in this study was from the white grape Vitis vinifera var. Treixadura. Immediately after the grapes were pressed in an industrial pneumatic press (maximum 160 kPa with a total time of 3 h) the resulted mass (skins, stalks and seeds) was stored, for the alcoholic fermentation of the residual sugars, in four different types of containers, selected for being habitual in the conservation of grape marc. The initial grape marc composition was the same in all cases (pH 3.3; total acidity = 6.25 g tartaric acid L 1 and 73 g kg 1 of reducing sugars). The containers employed and their characteristics are the following: plastic drums of 250 kg capacity, with a screw-cap that had a small hole to allow the CO2 generated during fermentation to escape, 50 kg plastic sacks, 1000 kg plastic sacks, protected with external nylon fabric, 70,000 kg capacity silos, built of cement and covered internally with epoxy paint. The latter three systems do not allow hermetic closure of the pomace. Sacks were tied with cords, as tight as possible, and silos were usually closed by covering them with plastics, placing sand and wood on top to seal them. Despite a greater unit cost, the plastic drums and 1000 kg sacks allow to be reused, whereas the 50 kg sacks have to be renewed each year. Silos are fixed installations in the winery or distillery. The number of samples in each group was: six plastic drums, four plastic sacks (50 kg), six plastic sacks (1000 kg) and eight concrete containers (70,000 kg). For each distillation process, the volume of the raw material charged in the still was 800 kg. An industrial distillation unit using entrainment with steam and equipped with a rectification column was employed to distillate the raw material. For each container the distillation was made by duplicate and the distillate obtained (hearts between 85% and 30% (v/v) of ethanol) in each distillation process was collected in an individual tank. Heads and tails were separated. After homogenisation, a bottle of sample (0.75 L) was retired from each tank to gas chromatographic analysis. 2.2. Reagents Ethanol, of analytical grade, was purchased from Merck (Germany). 2-Butanol, 1-butanol, 1-propanol, 2-methyl-1-propanol, 4-methyl-2-pentanol, trans-2-hexenol, benzaldehyde, acetaldehyde, 1,1-diethoxyethane, diethyl succinate and ethyl mirystate, were supplied by Aldrich (Aldrich Chemical, Switzer-
land), methanol, benzyl alcohol, 2-phenylethanol, allyl alcohol, 2methyl-1-butanol, hexanol, ethyl butyrate, ethyl laurate, hexyl acetate, isoamyl acetate, ethyl acetate and methyl acetate, were purchased from Merck (Germany), ethyl hexanoate, ethyl octanoate, ethyl decanoate, trans-3-hexenol, cis-3-hexenol, 3-methyl-1butanol, furfural were supplied by Fluka (Switzerland) and ethyl lactate from Sigma (Switzerland). A stock solution of references standards was prepared in distilled water containing 40% (v/v) of ethanol. The range of concentration for each standard was established taking into account the concentration of these volatile compounds in this kind of beverage. The internal standard was 4-methyl-2-pentanol (5 g per 1 L of ethanol). 2.3. Chromatographic analysis For determination of the major volatile compounds (methanol, aldehydes, higher alcohols, acetates and ethyl esters), 1 mL of an internal standard solution (5 g of 4-methyl-2-pentanol per 1 L of ethanol) was added to 10 mL of sample. 1 lL aliquot was injected directly into the chromatograph and split 1:1. The analyses were carried out using a Hewlett Packard 5890 Series II Gas-Chromatograph equipped with an HP 6890 Automatic Injector. The compounds were separated on a Chrompack CP-WAX 57CB (polyethylene glycol stationary phase; 50 m 0.25 mm id with 0.25 lm film thickness) fused-silica capillary column. Instrumental conditions were: injector temperature: 250 °C, detector temperature: 260 °C, carrier gas: helium at 1.07 mL min 1; make-up gas: nitrogen 15 mL min 1. The detector gas flow rates were: hydrogen, 40 mL min 1; air, 400 mL min 1. The temperature program of the oven was as followed: Initial Ta: 40 °C (isotherm for 6 min). Ramp: 1.5 °C min 1 to 80 °C and afterwards to 200 °C at a rate of 3 °C min 1. Volatile compounds were identified by comparing retention times with those of pure compounds and confirmed by GC–MS using a HP5890 Series II coupled to HP 5989 A mass spectrometer. Positive ion electron impact spectra at 70 eV were recorded in the range m/z 10–1000 for scan runs. In the quantitative analyses, the response factor of each compound, RFi, was calculated by RFi = (Ais/Asi) (Csi/Cis), where Ais and Asi are the peak areas of the chromatographic internal standard and of the chromatographic standard of the compound of interest, respectively, and where Cis and Csi are the concentrations of the chromatographic internal standard and of the chromatographic standard of the compound of interest, respectively. In the quantification, the concentration of each compound of interest, Ci, was determined via Ci = (Ai/Ais) Cis RFi, where Ai is the areas of peak of interest. All determinations were performed in triplicate. 2.4. Statistical analysis A computer programme, Statgraphics Plus for Windows, Version 3.1 (1997), was used for the statistical study of the results. A Multifactor Analysis of Variance (ANOVA) was applied to establish whether significant differences (p < 0.05) existed between the values obtained for the mean concentration of volatile compounds in the different distillates analyzed. The Multiple Range Test (Tukey HSD) was applied to confirm the results obtained. 3. Results and discussion The results presented in Table 1 are the mean concentration for each volatile compound in the 24 grape marc distillates grouped according to the raw-material storage system.
S. Cortés et al. / Food Control 21 (2010) 1545–1549 Table 1 Mean values (mg/L) of major volatile compounds from Orujo distillates using different types of containers to grape pomace storage. ANOVA results are also showed. Compound
Plastic drums (250 kg)
Plastic sacks (50 kg)
Plastic sacks (1000 kg)
Concrete container (70,000 kg)
Samples (n)
6
4
6
8
Alcohols Ethanol (% v/v) Methanol 2-Butanol 1-Propanol 2-Methyl-1-propanol 1-Butanol 2-Methyl-1-butanol 3-Methyl-1-butanol 1-Hexanol Cis-3-hexen-1-ol Trans-3-hexen-1-ol Trans-2-hexen-1-ol Allyl alcohol Benzyl alcohol 2-Phenylethanol
69.2a 3558a 54.2a 452a,b 680a 46.4a 595a 1867a 56.7a 3.85a 0.44a 0.58a 10.48a 0.25a 53.5a
75.6a,b 6704b,c 640b 570b 369b 9.9b 190b 600b 98.7a,b 10.10a 3.59b 3.75a,b 7.65a,b 2.14b 9.6b
80.3b 4421a,b 1.42a 329a 675a 20.5b 464a,c 1706a 102.3b 5.99a 2.04a,b 1.49a,b n.d. 0.14a 14.4b
73.3a 6894c 194a,b 380a,b 609a,b 12.2b 409c 1367a 90.9a,b 4.60a 1.54a,b 5.23b 3.94b 1.63b 23.5b
Acetales and ethyl esters Methyl acetate Ethyl acetate Isoamyl acetate Hexyl acetate Ethyl butyrate Ethyl hexanoate Ethyl octanoate Ethyl decanoate Diethyl succinate Ethyl laurate Ethyl myristate Ethyl lactate
7.1a 3572a 50.9a 7.6a,b 9.49a 15.1a 141a 163a,c 93.5a 113a 12.2a 444a
24.01b 1068b 12.9b 3.1a 4.96a,b 14.2a 3.59b 0.99b 59.8b 41.5b 4.0b 744a
n.d. 525b 10.5b 5.55a 3.40b 8.3a 8.5b 223a 33.6b 65.6b 7.8a,b 121b
15.8a,b 1111b 6.69b 15.5b 2.16b 5.7a 40.9c 98.2c,b 39.5b 45.6b 8.5a,b 606a
Aldehydes and acetal Acetaldehyde 1,1-Diethoxyethane Furfural Benzaldehyde
446a 58.9a 19.8a 6.4a
87.3b 13.9b 5.9a 2.1a
243c 25.2b 4.9a 1.8a
82.9b 12.7b 10.1a 3.5a
n.d.: no detected. Values followed by the same letter are not significantly different at 95% confidence (Test Tukey HSD).
3.1. Alcohols Methanol is not a direct fermentation by-product; it is formed from pectin by pectolytic enzymes. This volatile compound has no influence on the aroma but it is important to limit its content because of its high potential toxicity (Silva, Macedo, & Malcata, 2000). The EC legislation (EC, 1989) limits the maximum concentration of methanol in alcoholic beverage in 1000 g/100 L absolute ethanol. In this study, the mean concentration of methanol was significantly higher for the distillate of the pomace stored in the concrete containers. The mean concentration of methanol in distillates of pomace stored in 50 kg sacks was similar to that achieved in concrete containers. In distillates of pomace stored in plastic drums and 1000 kg sacks the concentrations of methanol were significantly lower. Higher alcohols, or fusel oils, formed during alcoholic fermentation, are quantitatively the major group of volatile compounds in distillates. They have a notable influence on the sensory properties of this kind of alcoholic beverages (Nykänen, 1986). The European regulations establish that the minimum requirements of these volatile compounds must be higher than 140 g/HL a.a. According to previous studies (Cortés, Gil, & Fernández, 2009; Silva & Malcata, 1998), the presence of 1-propanol and 2-butanol in high concentrations could be a bacterial spoilage index. Pomaces stored in 50 kg sacks produced a distillate with a significantly high concentration of 2-butanol and 1-propanol, even higher than in the distillate from the concrete containers that, because of their size and
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conditions, tend to be a storage system that increases the concentration of both compounds (Cortés et al., 2006). On the contrary, distillates from 1000 kg sacks showed the lowest values. 2-Methyl-1-propanol is usually found in higher concentration than 1-propanol and according to Silva et al. (2000) contributes with favourable keynotes to spirits. The results obtained showed that the concentration of 2-methyl-1-propanol was significantly lower in the case of pomace stored in 50 kg sacks and higher in plastic drums and 1000 kg sacks. The relation between 1-propanol/2-methyl-1-propanol, proposed by Cantagrel, Maignial, Ferrari, and Snakkers (1998) as an indication of bacterial degradation, is higher for grape pomace distillate ensilaged in 50 kg saks (1.54) and lower in 1000 kg saks (0.49). 1-Butanol showed a concentration significantly higher in the case of distillates from plastic drums, related with bacterial spoilage. 2-Methyl-1-butanol and 3-methyl-1-butanol (amyl alcohols) are the higher alcohols most abundant in distillates. Amyl alcohols contribute with aromatic notes like ‘‘alcoholic”, ‘‘sweet” and ‘‘choking” (Flouros, Apostolopoulou, Demertzis, & Akrida-Demertzi, 2003) and a low concentration of both compounds are associated with light-bodied grape pomace spirits (Silva et al., 2000). Amyl alcohols were detected in significantly higher concentration in distillates from pomace stored in plastic drums, whilst a significantly lower concentration was found in distillates from pomace stored in 50 kg plastic sacks. According to Berry (1995) a high temperature and oxygen contact, during storage, increase the concentration of higher alcohols. Distillates from pomace stored in 50 kg sacks were the ones that present the lowest mean concentration of higher alcohols and, therefore, the resulting distillate will be possibly characterised with a light-bodied, an interesting aspect to be taken into account when selecting the storage container. Hexanol and hexenols contribute with ‘‘herbaceous”, ‘‘cut-grass” and ‘‘pungent” notes (De Rosa & Castagner, 1994), so they have a positive influence on the spirit aroma at low concentrations. 1-Hexanol was detected, in significantly higher concentration, in distillates from pomace stored in plastic sacks (1000 kg). In all distillates analyzed in this study, the hexanol content is upper than 10 g/HL a.a. that Ertan Anli, Vural, and Gucer (2007) established as a maximum content to avoid a grassy flavour in the distillate, aspect negative both to smell and taste (Silva et al., 2000). Cis-3-hexen-1-ol was the hexenol most abundant, except in pomace stored in concrete containers. No significant differences were established for the content of this compound between the distillates analyzed. The distillate from pomace stored in 50 kg plastic sacks showed the highest content of trans-3-hexen-1-ol, whereas trans-2-hexen-1-ol was more abundant in the distillate from the pomace stored in concrete containers. Allyl alcohol in high concentration is an indication of bad storage of the raw material. In this study its concentration was significantly higher in the distillate from the pomace stored in plastic drums. Allyl alcohol was not detected in distillates from pomace stored in 1000 kg sacks, confirming their advantageous. The content of benzyl alcohol in distillates from pomace stored in plastic drums and 1000 kg sacks was significantly lower than those found in pomace stored in 50 kg sacks and in concrete containers. 2-Phenylethanol is an aromatic alcohol produced during the alcoholic fermentation. This compound has a positive influence on the spirit aroma by its floral notes (De Rosa & Castagner, 1994). 2-Phenylethanol was significantly higher in distillates from pomace stored in plastic drums. 3.2. Acetates and ethyl esters The presence of high concentrations of methyl and ethyl acetate in distillates is a consequence of grape pomace storage in
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Volatile compounds 80
Concentration (mg/L)
70 60
Plastic Drums (250kg) Plastic Sacks (50 kg)
50
Plastic Sacks (1000 kg) Concrete Container (70000kg)
40 30 20 10 0 methanol/100
Higher
C6 compounds acetates /100
ethyl esters
alcohols/100
aldehydes and acetal/100
Fig. 1. Mean and standard deviation of volatile compounds families.
aerobiosis. Methyl acetate was significantly higher in distillates from pomace stored in 50 kg sacks and ethyl acetate in distillates from plastic drums. Ethyl acetate, in high concentration, has a negative influence to the aroma, contributing with ‘‘glue” notes (De Rosa & Castagner, 1994). The absence of methyl acetate and the low content of ethyl acetate in distillates from 1000 kg sacks, continues to support the suitability of this type of container for storing the raw material. Isoamyl and hexyl acetate are positive to the aroma, increasing the fruity notes, ‘‘banana” and ‘‘apple” (Francis & Newton, 2005). Both compounds were detected in significantly higher concentration in distillates from plastic drums. Three statistically differentiated groups can be established for the 4–10 carbon atom ethyl esters detected: the distillates from pomace stored in plastic drums with a significantly higher content, those stored in 50 kg sacks with the lowest content and the pomace distillates from 1000 kg plastic sacks and concrete container that had an intermediate value of this group of compounds. The rest of ethyl esters, ethyl succinate ethyl laurate and ethyl myrystate, were significantly more abundant in the distillates of pomace stored in plastic drums, too. Ethyl lactate is an important ester in grape pomace spirits. A high concentration of this volatile compound indicates a deficient and lengthy storage of the raw material causing contamination of the pomace by lactic bacteria. In this study, significantly lower concentrations of this compound were detected in the distillates from pomace stored in 1000 kg sacks, which again confirms the advantages of this type of container. 3.3. Aldehydes and acetal Aldehydes are found in alcoholic beverages as a result of spontaneous or microbially mediated oxidation (Apostolopoulou, Flouros, Demertzis, & Akrida-Demertzi, 2005; Flouros et al., 2003). As also occurs with ethyl acetate, acetaldehyde develops from storage of the pomace in the presence of oxygen or a deficient separation of the heads fraction (Soufleros & Bertrand, 1987). In grape marc distillates acetaldehyde is the major carbonyl compound (Silva & Malcata, 1999; Silva et al., 2000) and contributes to the sensory quality with descriptors like ‘‘nutty” and ‘‘overripe bruised apples” (De Rosa & Castagner, 1994). The distillates of pomace stored in plastic drums showed a concentration of acetaldehyde significantly higher, whereas the significant lowest concentration was detected in the distillates from pomace stored in 50 kg sacks and in the big
concrete containers. Acetal (1,1-diethoxyethane) was detected in significantly higher concentration in the distillates from pomace stored in plastic drums. Furfural and benzaldehyde did not present significantly different average concentrations in the distillates stored in the four types of containers. The concentration of furfural is not related to the storage system. This compound is formed by the acid hydrolysis or heating of pentoses (non-fermentable sugars) and/or Maillard reactions during distillation (Cole & Noble, 1997; Ebeler, Terrien, & Butzke, 2000). Furfural contents in distillates can increase employing a direct-fire pot distillation system (Mangas, Rodríguez, Moreno, & Blanco, 1996), this explain the lower concentration of this compound in the present study. Furfural contributes to the distillate aroma with ‘‘coconut”, ‘‘almond” and ‘‘nutty” notes (Monica-Lee, Paterson, & Piggot, 2000). According to Versini, Monetti, Dalla Serra, and Inama (1990), the formation of benzaldehyde is associated with microbiological development during the storage process. Fig. 1 shows the differences between four groups of distillates according with the total concentration of volatiles from each family. Grape marc storage in plastic drums produced distillates with lower contents of methanol and C6 compounds and a high content in the group of volatile compounds with sensorial positive qualities to the aroma and mouth of the spirit, ethyl esters and higher alcohols, respectively. However is difficult to control the aerobic bacteria spoilage, so the concentrations of ethyl acetate and aldehydes and acetal are high too. The grape marc stored in plastic sacks (50 kg) was easily deteriorated and produce high content of methanol and C6 compounds. Pomace stored in plastic sacks (1000 kg) produced distillates with low values of the majority volatile compounds analyzed, that implies a good sanitarity quality but a poor aromaticity. The results show that it is possible to obtain a good quality spirit from grape marc storage in high capacity concrete containers; however they contain the higher value of methyl alcohol, so some storage conditions (pH, temperature and humidity) must be controlled. 4. Conclusions The storage system employed in the conservation of raw material has a decisive influence on the presence and concentration of many of the volatile compounds present in pomace distillates. Grape marc stored in 50 kg sacks gives rise to a low quality distillate with high contents of methanol, 2-butanol, 1-propanol and
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ethyl lactate, products from degradation of the raw material. Despite the hermetic closure of 250 kg plastic drums, a deficient loading process or poor storage can cause a substantial increase in the concentration of compounds that are result of aerobic bacteria, such as ethyl acetate and acetaldehyde, however if this variable is controlled, distillates obtained are the high quality, more aromatics, with body in mouth and more complexity. Sacks (1000 kg) provide satisfactory storage of raw material and originate distillates with good characteristics. However, they are not very aromatic distillates, since they present low values of concentration for most of the ethyl esters determined, possibly a consequence of a rapid alcoholic fermentation. Despite the presumption that the obtention of good quality distillates from pomace stored in large-capacity silos is difficult, the results indicate that, under equal conditions, the average concentrations for a large number of the major compounds of the distillate have no significant differences to those found in the other lower capacity storage systems. References Apostolopoulou, A. A., Flouros, A. I., Demertzis, P. G., & Akrida-Demertzi, K. (2005). Differences in concentration of principal volatile constituents in traditional Greek distillates. Food Control, 16, 157–164. Berry, D. R. (1995). Alcoholic beverage fermentations. In A. G. H. Lea & J. R. Piggott (Eds.), Fermented beverage production (pp. 32–44). Wester Cleddens Road, Bishopbriggs, Glasgow, UK: Blackie Academic and Professional. Cantagrel, R., Maignial, L., Ferrari, G., & Snakkers, G. (1998). Elaboration du cognac la qualite se controle a chaque etape. In Proceedings of the XXIII Congrès Mondial de la Vigne et du Vin. (pp. II-472–II-490). Lisboa, Portugal: Instituto da Vinha e do Vinho. Cole, V. C., & Noble, A. C. (1997). Flavor chemistry and assessment. In A. G. H. Lea & J. R. Piggott (Eds.), Fermented beverage production (pp. 361–385). Wester Cleddens Road, Bishopbriggs, Glasgow, UK: Blackie Academic and Professional. Cortés, S., Gil, L., & Fernández, E. (2001). Concentration of volatiles in Marc Distillates from Galicia according to storage conditions of the grape pomace. Chromatographia, 53, 406–411. Cortés, S., Gil, L., & Fernández, E. (2006). Grape pomace in concrete containers. Influence of layer depth and storage time on the volatile composition of Orujo distillate. Deutsche Lebensmittel-Rundschau, 102, 373–377. Cortés, S., Gil, L., & Fernández, E. (2009). Chemical affinities between the major volatile compounds present in grape pomace distillate. Journal of the Science of Food and Agriculture, 89, 1221–1226. Da Porto, C. (2002). Volatile composition of ‘‘grappa low wines” using different methods and conditions of storage on an industrial scale. International Journal of Food Science and Technology, 37, 395–402.
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Food Control journal homepage: www.elsevier.com/locate/foodcont
The storage of grape marc: Limiting factor in the quality of the distillate Sandra Cortés *, José Manuel Salgado, Noelia Rodríguez, José Manuel Domínguez Department of Chemical Engineering, Sciences Faculty, University of Vigo, Campus Ourense, As Lagoas s/n, 32004 Ourense, Spain Laboratory of Agro-Food Biotechnology, CITI-Tecnólopole, Parque Tecnológico de Galicia, San Cibrao das Viñas, Ourense, Spain
a r t i c l e
i n f o
Article history: Received 12 September 2008 Received in revised form 27 March 2010 Accepted 3 April 2010
Keywords: Grape marc Storage system Volatile compounds
a b s t r a c t Grape marc, the mass of skins, stalks and seeds left after the winemaking process, is stored before distillation to produce ethanol by the alcoholic fermentation of the residual sugars. In this work 24 samples of grape marc were stored in four different types of containers. After distillation process, the samples obtained were analyzed by GC–MS to evaluate the influence that the storage exercises on the major volatile composition. Grape marc stored in plastic sacks (1000 kg) produced distillates with low values of the majority volatile compounds, that implies a good quality but a poor aromaticity. Distillates from pomace in plastic drums (250 kg) showed a high content in ethyl esters and higher alcohols, however the concentrations of ethyl acetate and aldehydes and acetal are high too, due to the difficulty to control the aerobic bacteria spoilage. The principal problem of the concrete containers (70,000 kg) is the high methanol production and in the plastic sacks (50 kg) the quick aerobic and anaerobic degradation. With an exhaustive control of oxygen contact, plastic drums and plastic sacks (1000 kg) were the better systems to storage grape marc before distillation. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Orujo is a traditional spirit of Galicia (winegrowing region of NW Spain) obtained by distillation of the vinification sub-products (stalks, skins, pulp and seeds) called grape marc or pomace. As a result, this alcoholic beverage is not only an important source of income for the Galician winegrowing sector, but also a method of making better use of grape residues (pomace), which is also important from the environmental point of view. The production and commercialisation of Orujo in Galicia must be adjusted to the norms reflected in the regulations for the Geographic Denomination of the Aguardientes and Traditional Liquors of Galicia. Other European spirits are produced like Orujos (i.e. Italian Grappas, Greek Tsipouro, French Marc and Portuguese Bagaçeiras). They are similar in terms of raw material, manufacturing techniques and sensorial properties. After pressing the grapes, pomace is stored under anaerobic conditions in order to promote spontaneous alcoholic fermentation of the residual sugars content. Distillation takes place after this alcoholic fermentation, but in some distilleries grape marc is stored during several months before distillation and depending on the storage conditions, methods and systems; the pomace preservation from bacteria and mould is difficult and in the distillate could appear off-flavours (Da Porto, 2002). The bibliographic
* Corresponding author. E-mail address: [email protected] (S. Cortés). 0956-7135/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2010.04.029
references that exist on the characteristics and conditions of this important stage indicate, among others, that the grape marc must be stored in the absence of oxygen, in small containers, and that storage should not be prolonged, although it must be sufficient to complete the alcoholic fermentation while avoiding the proliferation of microorganisms (Cortés, Gil, & Fernández, 2001, 2006; Da Porto, 2002; Usseglio-Tomasset, 1971; Versini & Odello, 1990; Williams & Strauss, 1978). Principally, they are acetic, lactic and butyric bacteria that would cause undesirable secondary fermentations through the formation of a series of volatile compounds with negative aromatic connotations, which notably degrade the sensorial quality of the resulting distillate (De Rosa & Castagner, 1994; Desauziers, Avezac, & Fanlo, 2000; Nykänen, 1986; Silva & Malcata, 1998). Among these compounds should be mentioned: ethyl acetate, the acetic, butyric and propionic acids, 2-butanol and ethyl esters of long-chain fatty acids. The correct selection of storage container for grape marc is one of the most important points of this stage. In general, this selection is directly related to the capacity and production of the distillery or winery and not so much dependent on the characteristics of the container. Medium-to-small producers tend to use small bins and sacks as containers, generally made from plastic. When the winery has a higher production, these methods of storage for grape marc cannot be used, as their installations are not prepared for storing a large number of small containers, nor would it be economically viable. In these cases, the distilleries construct large-capacity containers, called silos, which allow the storage of various tons of grape marc.
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The characteristics of each of the storage containers employed are different, not only in capacity, but also in type of material, design, facility of manipulation, resistance and duration. Therefore, their role with respect to the conservation of the pomace will also be different and it will be necessary to combine production and quality criteria in order to decide which storage system will be the most adequate in each case. Samples of grape marc stored in four different types of containers were used for this study. Following the corresponding distillation process, the major volatile compounds were determined by gas chromatography–mass spectrometry. The object of this study was to determine the chemical composition of the distillates, as a function of the raw-material storage system and to establish the possible significant differences in the mean concentration of each volatile compound, in the different storage systems studied. The results obtained will allow the establishment of a series of criteria for the selection of a storage system that will permit a better quality of the final product, Orujo. 2. Materials and methods 2.1. Samples and containers Grape marc employed in this study was from the white grape Vitis vinifera var. Treixadura. Immediately after the grapes were pressed in an industrial pneumatic press (maximum 160 kPa with a total time of 3 h) the resulted mass (skins, stalks and seeds) was stored, for the alcoholic fermentation of the residual sugars, in four different types of containers, selected for being habitual in the conservation of grape marc. The initial grape marc composition was the same in all cases (pH 3.3; total acidity = 6.25 g tartaric acid L 1 and 73 g kg 1 of reducing sugars). The containers employed and their characteristics are the following: plastic drums of 250 kg capacity, with a screw-cap that had a small hole to allow the CO2 generated during fermentation to escape, 50 kg plastic sacks, 1000 kg plastic sacks, protected with external nylon fabric, 70,000 kg capacity silos, built of cement and covered internally with epoxy paint. The latter three systems do not allow hermetic closure of the pomace. Sacks were tied with cords, as tight as possible, and silos were usually closed by covering them with plastics, placing sand and wood on top to seal them. Despite a greater unit cost, the plastic drums and 1000 kg sacks allow to be reused, whereas the 50 kg sacks have to be renewed each year. Silos are fixed installations in the winery or distillery. The number of samples in each group was: six plastic drums, four plastic sacks (50 kg), six plastic sacks (1000 kg) and eight concrete containers (70,000 kg). For each distillation process, the volume of the raw material charged in the still was 800 kg. An industrial distillation unit using entrainment with steam and equipped with a rectification column was employed to distillate the raw material. For each container the distillation was made by duplicate and the distillate obtained (hearts between 85% and 30% (v/v) of ethanol) in each distillation process was collected in an individual tank. Heads and tails were separated. After homogenisation, a bottle of sample (0.75 L) was retired from each tank to gas chromatographic analysis. 2.2. Reagents Ethanol, of analytical grade, was purchased from Merck (Germany). 2-Butanol, 1-butanol, 1-propanol, 2-methyl-1-propanol, 4-methyl-2-pentanol, trans-2-hexenol, benzaldehyde, acetaldehyde, 1,1-diethoxyethane, diethyl succinate and ethyl mirystate, were supplied by Aldrich (Aldrich Chemical, Switzer-
land), methanol, benzyl alcohol, 2-phenylethanol, allyl alcohol, 2methyl-1-butanol, hexanol, ethyl butyrate, ethyl laurate, hexyl acetate, isoamyl acetate, ethyl acetate and methyl acetate, were purchased from Merck (Germany), ethyl hexanoate, ethyl octanoate, ethyl decanoate, trans-3-hexenol, cis-3-hexenol, 3-methyl-1butanol, furfural were supplied by Fluka (Switzerland) and ethyl lactate from Sigma (Switzerland). A stock solution of references standards was prepared in distilled water containing 40% (v/v) of ethanol. The range of concentration for each standard was established taking into account the concentration of these volatile compounds in this kind of beverage. The internal standard was 4-methyl-2-pentanol (5 g per 1 L of ethanol). 2.3. Chromatographic analysis For determination of the major volatile compounds (methanol, aldehydes, higher alcohols, acetates and ethyl esters), 1 mL of an internal standard solution (5 g of 4-methyl-2-pentanol per 1 L of ethanol) was added to 10 mL of sample. 1 lL aliquot was injected directly into the chromatograph and split 1:1. The analyses were carried out using a Hewlett Packard 5890 Series II Gas-Chromatograph equipped with an HP 6890 Automatic Injector. The compounds were separated on a Chrompack CP-WAX 57CB (polyethylene glycol stationary phase; 50 m 0.25 mm id with 0.25 lm film thickness) fused-silica capillary column. Instrumental conditions were: injector temperature: 250 °C, detector temperature: 260 °C, carrier gas: helium at 1.07 mL min 1; make-up gas: nitrogen 15 mL min 1. The detector gas flow rates were: hydrogen, 40 mL min 1; air, 400 mL min 1. The temperature program of the oven was as followed: Initial Ta: 40 °C (isotherm for 6 min). Ramp: 1.5 °C min 1 to 80 °C and afterwards to 200 °C at a rate of 3 °C min 1. Volatile compounds were identified by comparing retention times with those of pure compounds and confirmed by GC–MS using a HP5890 Series II coupled to HP 5989 A mass spectrometer. Positive ion electron impact spectra at 70 eV were recorded in the range m/z 10–1000 for scan runs. In the quantitative analyses, the response factor of each compound, RFi, was calculated by RFi = (Ais/Asi) (Csi/Cis), where Ais and Asi are the peak areas of the chromatographic internal standard and of the chromatographic standard of the compound of interest, respectively, and where Cis and Csi are the concentrations of the chromatographic internal standard and of the chromatographic standard of the compound of interest, respectively. In the quantification, the concentration of each compound of interest, Ci, was determined via Ci = (Ai/Ais) Cis RFi, where Ai is the areas of peak of interest. All determinations were performed in triplicate. 2.4. Statistical analysis A computer programme, Statgraphics Plus for Windows, Version 3.1 (1997), was used for the statistical study of the results. A Multifactor Analysis of Variance (ANOVA) was applied to establish whether significant differences (p < 0.05) existed between the values obtained for the mean concentration of volatile compounds in the different distillates analyzed. The Multiple Range Test (Tukey HSD) was applied to confirm the results obtained. 3. Results and discussion The results presented in Table 1 are the mean concentration for each volatile compound in the 24 grape marc distillates grouped according to the raw-material storage system.
S. Cortés et al. / Food Control 21 (2010) 1545–1549 Table 1 Mean values (mg/L) of major volatile compounds from Orujo distillates using different types of containers to grape pomace storage. ANOVA results are also showed. Compound
Plastic drums (250 kg)
Plastic sacks (50 kg)
Plastic sacks (1000 kg)
Concrete container (70,000 kg)
Samples (n)
6
4
6
8
Alcohols Ethanol (% v/v) Methanol 2-Butanol 1-Propanol 2-Methyl-1-propanol 1-Butanol 2-Methyl-1-butanol 3-Methyl-1-butanol 1-Hexanol Cis-3-hexen-1-ol Trans-3-hexen-1-ol Trans-2-hexen-1-ol Allyl alcohol Benzyl alcohol 2-Phenylethanol
69.2a 3558a 54.2a 452a,b 680a 46.4a 595a 1867a 56.7a 3.85a 0.44a 0.58a 10.48a 0.25a 53.5a
75.6a,b 6704b,c 640b 570b 369b 9.9b 190b 600b 98.7a,b 10.10a 3.59b 3.75a,b 7.65a,b 2.14b 9.6b
80.3b 4421a,b 1.42a 329a 675a 20.5b 464a,c 1706a 102.3b 5.99a 2.04a,b 1.49a,b n.d. 0.14a 14.4b
73.3a 6894c 194a,b 380a,b 609a,b 12.2b 409c 1367a 90.9a,b 4.60a 1.54a,b 5.23b 3.94b 1.63b 23.5b
Acetales and ethyl esters Methyl acetate Ethyl acetate Isoamyl acetate Hexyl acetate Ethyl butyrate Ethyl hexanoate Ethyl octanoate Ethyl decanoate Diethyl succinate Ethyl laurate Ethyl myristate Ethyl lactate
7.1a 3572a 50.9a 7.6a,b 9.49a 15.1a 141a 163a,c 93.5a 113a 12.2a 444a
24.01b 1068b 12.9b 3.1a 4.96a,b 14.2a 3.59b 0.99b 59.8b 41.5b 4.0b 744a
n.d. 525b 10.5b 5.55a 3.40b 8.3a 8.5b 223a 33.6b 65.6b 7.8a,b 121b
15.8a,b 1111b 6.69b 15.5b 2.16b 5.7a 40.9c 98.2c,b 39.5b 45.6b 8.5a,b 606a
Aldehydes and acetal Acetaldehyde 1,1-Diethoxyethane Furfural Benzaldehyde
446a 58.9a 19.8a 6.4a
87.3b 13.9b 5.9a 2.1a
243c 25.2b 4.9a 1.8a
82.9b 12.7b 10.1a 3.5a
n.d.: no detected. Values followed by the same letter are not significantly different at 95% confidence (Test Tukey HSD).
3.1. Alcohols Methanol is not a direct fermentation by-product; it is formed from pectin by pectolytic enzymes. This volatile compound has no influence on the aroma but it is important to limit its content because of its high potential toxicity (Silva, Macedo, & Malcata, 2000). The EC legislation (EC, 1989) limits the maximum concentration of methanol in alcoholic beverage in 1000 g/100 L absolute ethanol. In this study, the mean concentration of methanol was significantly higher for the distillate of the pomace stored in the concrete containers. The mean concentration of methanol in distillates of pomace stored in 50 kg sacks was similar to that achieved in concrete containers. In distillates of pomace stored in plastic drums and 1000 kg sacks the concentrations of methanol were significantly lower. Higher alcohols, or fusel oils, formed during alcoholic fermentation, are quantitatively the major group of volatile compounds in distillates. They have a notable influence on the sensory properties of this kind of alcoholic beverages (Nykänen, 1986). The European regulations establish that the minimum requirements of these volatile compounds must be higher than 140 g/HL a.a. According to previous studies (Cortés, Gil, & Fernández, 2009; Silva & Malcata, 1998), the presence of 1-propanol and 2-butanol in high concentrations could be a bacterial spoilage index. Pomaces stored in 50 kg sacks produced a distillate with a significantly high concentration of 2-butanol and 1-propanol, even higher than in the distillate from the concrete containers that, because of their size and
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conditions, tend to be a storage system that increases the concentration of both compounds (Cortés et al., 2006). On the contrary, distillates from 1000 kg sacks showed the lowest values. 2-Methyl-1-propanol is usually found in higher concentration than 1-propanol and according to Silva et al. (2000) contributes with favourable keynotes to spirits. The results obtained showed that the concentration of 2-methyl-1-propanol was significantly lower in the case of pomace stored in 50 kg sacks and higher in plastic drums and 1000 kg sacks. The relation between 1-propanol/2-methyl-1-propanol, proposed by Cantagrel, Maignial, Ferrari, and Snakkers (1998) as an indication of bacterial degradation, is higher for grape pomace distillate ensilaged in 50 kg saks (1.54) and lower in 1000 kg saks (0.49). 1-Butanol showed a concentration significantly higher in the case of distillates from plastic drums, related with bacterial spoilage. 2-Methyl-1-butanol and 3-methyl-1-butanol (amyl alcohols) are the higher alcohols most abundant in distillates. Amyl alcohols contribute with aromatic notes like ‘‘alcoholic”, ‘‘sweet” and ‘‘choking” (Flouros, Apostolopoulou, Demertzis, & Akrida-Demertzi, 2003) and a low concentration of both compounds are associated with light-bodied grape pomace spirits (Silva et al., 2000). Amyl alcohols were detected in significantly higher concentration in distillates from pomace stored in plastic drums, whilst a significantly lower concentration was found in distillates from pomace stored in 50 kg plastic sacks. According to Berry (1995) a high temperature and oxygen contact, during storage, increase the concentration of higher alcohols. Distillates from pomace stored in 50 kg sacks were the ones that present the lowest mean concentration of higher alcohols and, therefore, the resulting distillate will be possibly characterised with a light-bodied, an interesting aspect to be taken into account when selecting the storage container. Hexanol and hexenols contribute with ‘‘herbaceous”, ‘‘cut-grass” and ‘‘pungent” notes (De Rosa & Castagner, 1994), so they have a positive influence on the spirit aroma at low concentrations. 1-Hexanol was detected, in significantly higher concentration, in distillates from pomace stored in plastic sacks (1000 kg). In all distillates analyzed in this study, the hexanol content is upper than 10 g/HL a.a. that Ertan Anli, Vural, and Gucer (2007) established as a maximum content to avoid a grassy flavour in the distillate, aspect negative both to smell and taste (Silva et al., 2000). Cis-3-hexen-1-ol was the hexenol most abundant, except in pomace stored in concrete containers. No significant differences were established for the content of this compound between the distillates analyzed. The distillate from pomace stored in 50 kg plastic sacks showed the highest content of trans-3-hexen-1-ol, whereas trans-2-hexen-1-ol was more abundant in the distillate from the pomace stored in concrete containers. Allyl alcohol in high concentration is an indication of bad storage of the raw material. In this study its concentration was significantly higher in the distillate from the pomace stored in plastic drums. Allyl alcohol was not detected in distillates from pomace stored in 1000 kg sacks, confirming their advantageous. The content of benzyl alcohol in distillates from pomace stored in plastic drums and 1000 kg sacks was significantly lower than those found in pomace stored in 50 kg sacks and in concrete containers. 2-Phenylethanol is an aromatic alcohol produced during the alcoholic fermentation. This compound has a positive influence on the spirit aroma by its floral notes (De Rosa & Castagner, 1994). 2-Phenylethanol was significantly higher in distillates from pomace stored in plastic drums. 3.2. Acetates and ethyl esters The presence of high concentrations of methyl and ethyl acetate in distillates is a consequence of grape pomace storage in
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Volatile compounds 80
Concentration (mg/L)
70 60
Plastic Drums (250kg) Plastic Sacks (50 kg)
50
Plastic Sacks (1000 kg) Concrete Container (70000kg)
40 30 20 10 0 methanol/100
Higher
C6 compounds acetates /100
ethyl esters
alcohols/100
aldehydes and acetal/100
Fig. 1. Mean and standard deviation of volatile compounds families.
aerobiosis. Methyl acetate was significantly higher in distillates from pomace stored in 50 kg sacks and ethyl acetate in distillates from plastic drums. Ethyl acetate, in high concentration, has a negative influence to the aroma, contributing with ‘‘glue” notes (De Rosa & Castagner, 1994). The absence of methyl acetate and the low content of ethyl acetate in distillates from 1000 kg sacks, continues to support the suitability of this type of container for storing the raw material. Isoamyl and hexyl acetate are positive to the aroma, increasing the fruity notes, ‘‘banana” and ‘‘apple” (Francis & Newton, 2005). Both compounds were detected in significantly higher concentration in distillates from plastic drums. Three statistically differentiated groups can be established for the 4–10 carbon atom ethyl esters detected: the distillates from pomace stored in plastic drums with a significantly higher content, those stored in 50 kg sacks with the lowest content and the pomace distillates from 1000 kg plastic sacks and concrete container that had an intermediate value of this group of compounds. The rest of ethyl esters, ethyl succinate ethyl laurate and ethyl myrystate, were significantly more abundant in the distillates of pomace stored in plastic drums, too. Ethyl lactate is an important ester in grape pomace spirits. A high concentration of this volatile compound indicates a deficient and lengthy storage of the raw material causing contamination of the pomace by lactic bacteria. In this study, significantly lower concentrations of this compound were detected in the distillates from pomace stored in 1000 kg sacks, which again confirms the advantages of this type of container. 3.3. Aldehydes and acetal Aldehydes are found in alcoholic beverages as a result of spontaneous or microbially mediated oxidation (Apostolopoulou, Flouros, Demertzis, & Akrida-Demertzi, 2005; Flouros et al., 2003). As also occurs with ethyl acetate, acetaldehyde develops from storage of the pomace in the presence of oxygen or a deficient separation of the heads fraction (Soufleros & Bertrand, 1987). In grape marc distillates acetaldehyde is the major carbonyl compound (Silva & Malcata, 1999; Silva et al., 2000) and contributes to the sensory quality with descriptors like ‘‘nutty” and ‘‘overripe bruised apples” (De Rosa & Castagner, 1994). The distillates of pomace stored in plastic drums showed a concentration of acetaldehyde significantly higher, whereas the significant lowest concentration was detected in the distillates from pomace stored in 50 kg sacks and in the big
concrete containers. Acetal (1,1-diethoxyethane) was detected in significantly higher concentration in the distillates from pomace stored in plastic drums. Furfural and benzaldehyde did not present significantly different average concentrations in the distillates stored in the four types of containers. The concentration of furfural is not related to the storage system. This compound is formed by the acid hydrolysis or heating of pentoses (non-fermentable sugars) and/or Maillard reactions during distillation (Cole & Noble, 1997; Ebeler, Terrien, & Butzke, 2000). Furfural contents in distillates can increase employing a direct-fire pot distillation system (Mangas, Rodríguez, Moreno, & Blanco, 1996), this explain the lower concentration of this compound in the present study. Furfural contributes to the distillate aroma with ‘‘coconut”, ‘‘almond” and ‘‘nutty” notes (Monica-Lee, Paterson, & Piggot, 2000). According to Versini, Monetti, Dalla Serra, and Inama (1990), the formation of benzaldehyde is associated with microbiological development during the storage process. Fig. 1 shows the differences between four groups of distillates according with the total concentration of volatiles from each family. Grape marc storage in plastic drums produced distillates with lower contents of methanol and C6 compounds and a high content in the group of volatile compounds with sensorial positive qualities to the aroma and mouth of the spirit, ethyl esters and higher alcohols, respectively. However is difficult to control the aerobic bacteria spoilage, so the concentrations of ethyl acetate and aldehydes and acetal are high too. The grape marc stored in plastic sacks (50 kg) was easily deteriorated and produce high content of methanol and C6 compounds. Pomace stored in plastic sacks (1000 kg) produced distillates with low values of the majority volatile compounds analyzed, that implies a good sanitarity quality but a poor aromaticity. The results show that it is possible to obtain a good quality spirit from grape marc storage in high capacity concrete containers; however they contain the higher value of methyl alcohol, so some storage conditions (pH, temperature and humidity) must be controlled. 4. Conclusions The storage system employed in the conservation of raw material has a decisive influence on the presence and concentration of many of the volatile compounds present in pomace distillates. Grape marc stored in 50 kg sacks gives rise to a low quality distillate with high contents of methanol, 2-butanol, 1-propanol and
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ethyl lactate, products from degradation of the raw material. Despite the hermetic closure of 250 kg plastic drums, a deficient loading process or poor storage can cause a substantial increase in the concentration of compounds that are result of aerobic bacteria, such as ethyl acetate and acetaldehyde, however if this variable is controlled, distillates obtained are the high quality, more aromatics, with body in mouth and more complexity. Sacks (1000 kg) provide satisfactory storage of raw material and originate distillates with good characteristics. However, they are not very aromatic distillates, since they present low values of concentration for most of the ethyl esters determined, possibly a consequence of a rapid alcoholic fermentation. Despite the presumption that the obtention of good quality distillates from pomace stored in large-capacity silos is difficult, the results indicate that, under equal conditions, the average concentrations for a large number of the major compounds of the distillate have no significant differences to those found in the other lower capacity storage systems. References Apostolopoulou, A. A., Flouros, A. I., Demertzis, P. G., & Akrida-Demertzi, K. (2005). Differences in concentration of principal volatile constituents in traditional Greek distillates. Food Control, 16, 157–164. Berry, D. R. (1995). Alcoholic beverage fermentations. In A. G. H. Lea & J. R. Piggott (Eds.), Fermented beverage production (pp. 32–44). Wester Cleddens Road, Bishopbriggs, Glasgow, UK: Blackie Academic and Professional. Cantagrel, R., Maignial, L., Ferrari, G., & Snakkers, G. (1998). Elaboration du cognac la qualite se controle a chaque etape. In Proceedings of the XXIII Congrès Mondial de la Vigne et du Vin. (pp. II-472–II-490). Lisboa, Portugal: Instituto da Vinha e do Vinho. Cole, V. C., & Noble, A. C. (1997). Flavor chemistry and assessment. In A. G. H. Lea & J. R. Piggott (Eds.), Fermented beverage production (pp. 361–385). Wester Cleddens Road, Bishopbriggs, Glasgow, UK: Blackie Academic and Professional. Cortés, S., Gil, L., & Fernández, E. (2001). Concentration of volatiles in Marc Distillates from Galicia according to storage conditions of the grape pomace. Chromatographia, 53, 406–411. Cortés, S., Gil, L., & Fernández, E. (2006). Grape pomace in concrete containers. Influence of layer depth and storage time on the volatile composition of Orujo distillate. Deutsche Lebensmittel-Rundschau, 102, 373–377. Cortés, S., Gil, L., & Fernández, E. (2009). Chemical affinities between the major volatile compounds present in grape pomace distillate. Journal of the Science of Food and Agriculture, 89, 1221–1226. Da Porto, C. (2002). Volatile composition of ‘‘grappa low wines” using different methods and conditions of storage on an industrial scale. International Journal of Food Science and Technology, 37, 395–402.
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