Colour and phenolic compounds in sweet red wines from Merlot and Tempranillo grapes chamber-dried under controlled conditions Ana Marquez, Maria P. Serratosa, Azahara Lopez-Toledano, Julieta Merida ⇑ Department of Agricultural Chemistry, Faculty of Sciences, University of Cordoba, Edificio Marie Curie, Campus de Rabanales, E-14014 Cordoba, Spain article info Article history: Received 6 April 2011 Received in revised form 21 June 2011 Accepted 5 July 2011 Available online 12 July 2011 Keywords: Red grapes Red wines Chamber-drying Phenolic compounds abstract Chamber drying under controlled temperature and humidity conditions of the red grape varieties Merlot and Tempranillo grown in Andalusia (Spain), and the fortification and maceration of the musts in the presence of skin from both types of grapes, to obtain sweet red wines, has been studied. Changes in colour and in monomeric and polymeric phenols during the vinification process were examined. Chamber dry- ing increased the sugar content to about 31.4 °Brix within 48 h in Merlot grapes and 72 h in Tempranillo grapes. This drying process also causes skin rupture, facilitating the access of phenolic compounds to the pulp. The resulting musts exhibited slight browning and increased red hues, due to a high concentration of anthocyanins; maceration in the presence of grape skins for 24 h provided the best results. The end- product contained highly acceptable tannin, colour and phenolic compounds for marketing as a high quality sweet red wine, in comparison with other commercial sweet red wines. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The Montilla–Moriles designation of origin (DO) in Andalusia (Spain) has traditionally produced nationally and internationally appreciated sweet wines from sun-dried Pedro Ximenez white grapes (Serratosa, Lopez-Toledano, Merida, & Medina, 2008a). Although Pedro Ximenez sweet wines are currently marketed at several DOs in Andalusia, they are largely produced from grapes grown in the Montilla–Moriles region, on account of its special cli- matic conditions, which include high temperatures and a very low relative humidity in August. Grape drying times in southern Spain typically range from 5 to 10 days, but can be somewhat longer depending on the particular climatic conditions. Sun-dried grapes are vulnerable to damage by insect attacks, occasional rain and fungal toxins, such as ochratoxin A(Serratosa, Lopez-Toledano, Medina, & Merida, 2008b; Serratosa, Lopez-Toledano, Millan, Medina, & Merida, 2010). This has pro- moted the development of alternative methods of fruits drying un- der controlled temperature and humidity conditions; such methods produce raisins of a similar quality to those obtained by sun-drying but in less time (Serratosa et al., 2008b). These fruits include cher- ries, figs, apricots or even raisins (Doymaz, 2006) for the production of sweet wines (Ruiz Bejarano, Rodriguez Dodero, & Barroso, 2010). Colour changes in grapes during the sun-drying process are a result of enzymatic and non-enzymatic browning reactions (Karadeniz, Durst, & Wrolstad, 2000) that include the formation of pigments under the action of polyphenol oxidase (PPO) enzymes on their phenolic substrates (particularly hydroxycinnamic acids). In healthy grapes, PPOs are found separated from polyphenols; however, physical damage of grape tissues by the effect of changes during the drying process can bring the enzymes into contact with their substrates and trigger browning reactions (Cheynier & Moutounet, 1992). In addition, browning can be the result of the Maillard reaction, a non-enzymatic process yielding coloured products known as ‘‘melanoidins’’ from free carbonyl and amino groups (Kim & Lee, 2008). The presence of amino acids and mono- saccharides in grapes, and the high concentrations of the latter compounds resulting from the drying of berries, facilitate the devel- opment of the Maillard reaction during their sun-drying. Also, the formation of melanoidins, which cause considerable browning in the resulting wine, is especially favourable above 50 °C(Rivero- Perez, Perez-Magariño, & Gonzalez-SanJose, 2002), a temperature level which can easily be surpassed under the typical climatic con- ditions of the Montilla–Moriles region. Anthocyanins play a central role in the colour of red wines, where they can confer hues ranging from orange to purple. The purplish red colour of young red wines is due to anthocyanins (3-monoglucosides and acetyl, p-coumaroyl and caffeoyl deriva- tives of delphinidin, cyanidin, petunidin, peonidin and malvidin) initially present in Vitis vinifera grapes (Pomar, Novo, & Masa, 2005). The production of red wines includes the maceration of the must in the presence of grape skins in order to maximise the extraction of anthocyanins and confer an appropriate colour to the wine. Maximum anthocyanin levels are observed during the first few days of maceration, after which no more extraction is 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.07.010 ⇑ Corresponding author. Tel.: +34 957 218 612; fax: +34 957 212 146. E-mail address: jmerida@uco.es (J. Merida). Food Chemistry 130 (2012) 111–120 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem