Wine-making with Protection of Must against Oxidation in a Warm, Semi-arid Terroir o. Corona Dipartimento di Ingegneria e Tecnologie Agro-Forestali, Universita degli Studi di Palermo, 90128 Palermo, Italy Submitted for publication: November 2009 Accepted for publication: March 201 0 Key words: Enzymatic oxidation, protection against oxidation To protect varietal aromas from oxidation before alcoholic fermentation, two grape must samples were prepared from white grapes potentially low in copper, pre-cooled and supplemented with ascorbic acid and solid CO (trial 2 ) B )' AC02 or S02 (trial S02 The wines prepared from musts protected from oxidation had aroma descriptors that included "passion fruit" and "grapefruit skin". The lower concentrations offtavanols in the AC02 trial demonstrated that the use of solid CO2 as an oxidation preventative instead of S02 reduced the extraction of these polyphenols from the grape solids. The higher concentration of hydroxycinnamoyl tartaric acids of the wine from the AC02 trial with respect to BS02 was ascribed to the lower grape polyphenoloxidase activity induced by the lower oxygen level AC02 B " in the trial, or to the combination of caftaric acid quinone with the S02 in S02 Although the grapes were very ripe (alcohol in wines ~ 14.5% vol), the wines made with musts prepared by the two techniques were characterised by aroma descriptors like "passion fruit" and "grapefruit skin", and these aromas were not detected in the wines prepared from unprotected musts. F or the production of white wine, the grapes are usually pressed Darriet el aI., 1995; Bouchilloux el ai., 1998; Tominaga el ai., after destemming and crushing, and the must that is obtained after 1998; Peyrot des Gachons el ai., 2000; Murat el ai., 2001), can settling is fermented by yeasts at a temperature that generally be oxidised, with a loss of the varietal characters of the wine. The is lower than 20 C C (Bely el ai., 1990). Enzymatic oxidation free thiols released by yeasts from the above precursors during reactions may begin during harvest and the transport of grapes fermentation (Dubourdieu el ai., 2006) can also be precipitated from the vineyard to the cellar, and are active at crushing (Iglesias by copper from anti-mildew treatments in the vineyard (Darriet el elal., 1991; Macheixelai., 1991; Rigaud elai., 1991; Spanos & ai., 2001). Therefore, if the wines are to express odorous thiols, Wrolstad, 1992). C6 saturated and unsaturated volatile aldehydes the must should be protected against oxidation (Rigaud el ai., and alcohols are the products of the oxidation of unsaturated 1990; Rigaud el ai., 2006), and vineyard treatments with copper­ fatty acids catalysed by grape lipoxygenase (Cayrel el aI., 1983; containing pesticides should be limited (Darriet el aI., 2001). Zamora el ai., 1985), and must browning is the result of polyphenol In this study, grape pre-cooling and two techniques to protect oxidation by grape polyphenol oxidase (PPO) (Wissemann & must against contact with atmospheric oxygen were tested in Lee, 1980; Singleton el ai., 1985; Singleton, 1987; Cheynier & order to minimise PPO activity and to obtain wines endowed with Ricardo da Silva, 1991). As polyphenols (mainly those of the class aroma descriptors ascribed to odorous thiols. The influence of of flavanols) are also involved in wine browning (Tulyathan el these techniques on the extraction of flavanols from grape solids ai., 1989; Fernandez-Zorbano el ai., 1995; Fernandez-Zorbano el was also studied. An additional aim of the experiments was to ai., 1998), their extraction from grape skin and seeds during must verify the possibility of producing wine from grape varieties that preparation should be minimised. In the presence of oxygen, PPO differed from Alsatian varieties but that still had aroma descriptors oxidises hydroxycinnamoyl tartaric acids, with the production ascribed to odorous thiols (Tominaga el ai., 2003). of caftaric acid quinone that can be reduced by glutathione (if present), and the production of2-S-glutathionyl caftaric acid (GRP, MATERIALS AND METHODS a colourless form) (Singleton el ai., 1987). Caftaric acid quinone Grapes and winemaking techniques can also oxidise the other must phenolics as well as the same GRP Vinification experiments were performed in 2006 with Grillo (Cheynier & Van Hulst, 1988), with the production of caftaric grapes from a vineyard in the Marsala terroir (western Sicily). acid and quinones (coupled oxidation-reduction reactions) that Grillo, a white variety indigenous to western Sicily, was used in give rise to the brown pigments responsible for must browning. the past to produce 1.1arsala wines, and is now used for quality In some cases, to reduce the phenolic content when the must is white wine production. The vineyard was trained to an espalier particularly rich in these compounds, PPO action is promoted system, with Guyot pruning, 12 to 15 buds/vine and a planting throughout the contact of must with oxygen or air (must oxidation density of 4 000 vineslha, corresponding to 2.5 x 1 m spacing. or hyper-oxidation) (Dubourdieu & Lavigne, 1990; Cheynier el Anti-mildew treatments with copper-containing pesticides were ai., 1993; Schneider, 1998). Unfortunately, if this technique is discontinued in mid-June, about two weeks after flowering. used, odorous thiols, a class of aromas that is present in some Grapes (2 000 kg) were picked on 2006-09-17, put into 10 to 12 grapes as cisteinyl derivatives (Darriet, 1993; Darriet el aI., 1993; kg plastic crates, moved to the winery and stored in a refrigerated *Corresponding author: e-mail address:[email protected] S. Afr. J. Enol. Vitic., Vol. 31, No.1, 2010 58 Protection ofM ust against CJxidation 59 room for about 30 hours at 8°C to avoid PPO activity at crushing the pH of the wine and that of the same wine to which 10 meqlL and the extraction of polyphenol when passed through a heat NaOH has been added (Usseglio-Tomasset, 1995). The reactivity exchanger. offlavanols to p-dimethylamino-cinnamaldehyde (p-DAC assay) Two experiments relating to the protection of must against was determined by UV- Vis spectrophotometry (Delcour & Janssens de Varebeke, 1985) (Beckman DU 640 spectrophotometer, Milan, oxidation by CO2 (Ac02) and S02 (BS02) were carried out, each on 1 000 kg of refrigerated grapes. Italy) as being (+)-catechin equivalent Hydroxycinnamoyl tartaric acids (HCTA) was tested by HPLC (Di Stefano & The first was the Ac02 trial, during which previously refrigerated Cravero, 1992). The standard employed was chlorogenic acid, grapes were destemmed, crushed and stored in a 10 hL vat in and the concentration ofHCTA was expressed as chlorogenic acid which previously solid CO (50 gllOO kg) had been placed. During 2 equivalents. By processing these data (hypothetical identity of £ crushing, 15 gllOO kg ascorbic acid, 0.8 mLlloo kg maceration for chI orogenic and caftaric acids at 220 nm and the data from the enzymes (Endozym ICS 10 Aromes, Pascal Biotech), 0.8 mLIlOO coefficients detennined by injecting free hydroxycinnamic acids kg pectolytic enzymes (Endozym ICS 10 Eclairs, Pascal Biotech) and chi orogenic acid), the concentration of caftaric, coutaric and and solid CO2 (50 gil 00 kg) were added. After cold maceration at fertaric acids was estimated. 2-S-g1utathionyl caftaric acid was 10°C for 24 hours, the crushed grapes were pressed (Drain Press evaluated as caftaric acid equivalent. The analysis of fixed acids SF 18, Puleo s.r.I., Marsala, Sicily). Prior to the introduction of was performed by HPLC on an Agilent series 2100 instrument the crushed grapes a small amount of solid CO was added to the 2 , (Milan, Italy) equipped with a C 18 column (Econosphere™ C 18 press, and the pressing was started after solid CO2 sublimation. 5 fill1, 250 x 4.6 mm i.d., Lokeren, Belgium, part n° 70066), After pressing (max 0.2 bar), free run must (6.5 hL) was sent to a volume injected 20 fjL, flow rate 0.6 mLimin., detection at 210 10 hL tank in which 50 gil 00 kg solid CO2 had been placed and nm. Prior to injection, 0.5 mL of sample was stripped of phenolics clarified by static settling at 10°C for 20 hours. The clear must (6 by passing it through a 400 mg C 18 Sep Pack cartridge (Sep Pak, hL) was acidified with 160 glhL tartaric acid, charged with 10 glhL Waters, Milan, Italy, part n° WAT03681O), activated with 2 mL diammonium phosphate (DAP) containing thiamine (0.25%), and 3 of methanol, followed by 3 mL of Hl04 10- M and elution with fennented by inoculation of 20 glhL reactivated dry yeast (Sinergie 3 Hl04 10- M until a volume of 10 mL was reached. Free volatiles Levuline CI9/ALS, Groupe Oeno France). During fennentation were detennined according to the method outlined by Gianotti and (the temperature was 18°C), when the amount of alcohol reached Di Stefano (1991). In brief, 25 mL of wine, charged with I-Hep­ 3% and 8% vol respectively, 10 and 5 glhL ofDAP were added and tanol as internal standard (0.25 mL of 40 mglL hydroalcoholic one-third of the must volume was pumped over in air. solution), diluted to 75 mL with distilled HP, were passed The second trial was the BS02 trial. In comparison to the through a 1 g C18 cartridge (Isolute, SPE Columns, Uppsala, AC02 trial, BS02 differed in the time of cold pre-fennentative Sweden, part n° 221-0100-C) previously activated with 3 mL maceration (three hours rather than the usual 24-hour period, to of methanol followed by 4 mL of distilled Hp. After washing avoid excessive extraction of phenolics induced by the presence with 30 mL of distilled HP, volatiles were recovered by elution of SO). Potassium meta-bisulphite (10 gllOO kg) was added to with 12 mL dichloromethane, dehydrated and evaporated to the crushed grapes instead of solid CO2.