Drying of Pedro Ximenez Grapes in Chamber at Controlled Temperature and with Dipping Pretreatments. Changes in the Color Fraction

Abstract

The drying of Pedro Ximenez grapes in chamber at a controlled temperature of 40 or 50 degrees C is studied. Compared to traditional sun-drying, the chamber-drying shortened the drying time by about 40% at 50 degrees C. In color terms, the musts obtained from grapes dried at 50 degrees C were closer in CIELab coordinates to those obtained by sun-dried grapes, with similar h(ab) values and slightly lower L* and C(ab)*. To shorten further the drying times at 50 degrees C, the grapes were dipped in olive oil or ethyl oleate emulsions containing potassium carbonate. The ethyl oleate pretreatment shortened additionally the drying time by about 25%, providing musts with chroma, lightness, and hue similar to those without grape pretreatment. In general, except for the phenolic compounds corresponding to the drying with ethyl oleate pretreatment, most of these compounds in the remainding conditions studied increased to a lesser extent than expected because of water losses of the grapes during drying, revealing degradation reactions.

Quality Improvement in Sweet Red Wines Through an Alternative Grape-Drying System

“…Thus, the A420 values for the traditional wines were approximately double (w2) and triple (w1) those of the all alternative wines (w3 to w5). These results are consistent with others previously found by Serratosa et al (2008a) in musts from sun-dried and chamber-dried Pedro Ximenez grapes. The increased progress of browning in the traditional wines can be ascribed to several factors.…”

“…In addition, the sensory properties of the alternative wines are likely to be highly acceptable for consumers. Based on previous works (Serratosa et al, 2008a), chamber drying has some other advantages over sun drying. Thus, controlled drying allows the use of grapes of variable ripening status in order to shorten the drying time needed to obtain raisins of similar sweetness and to increase must yield.…”

“…On the other hand, grape dehydration leads to important modifications in colour, volatile compounds and phenolic composition (Bellicontro et al, 2004;Serratosa et al, 2008a). In particular, the phenolic compounds present in the skins are diffused to the pulp due to their structural alterations (Marquez et al, 2012b).…”

Colour and phenolic compounds in sweet red wines from Merlot and Tempranillo grapes chamber-dried under controlled 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 promoted the development of alternative methods of fruits drying under 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 cherries, figs, apricots or even raisins (Doymaz, 2006) for the production of sweet wines (Ruiz Bejarano, Rodriguez Dodero, & Barroso, 2010).…”

Sun drying of seedless and seeded grapes

“…Grapes are covered naturally with a thin-layer of wax; hence, it is necessary to increase water transport from grape berries during drying process. Dipping in hot water or the use of chemicals such as sulphur, potassium meta bisulphide (KMS), potassium hydroxide (KOH), sodium hydroxide (NaOH), potassium carbonate (K 2 CO 3 ), and ethyl or methyl oleate emulsions are some of pretreatments widely used for fruit drying to increase drying rate and improve the colour quality of products (Mahmutoglu et al 1996;Di Matteo et al 2000;Kingsly et al 2007;Serratosa et al 2008;Bingol et al 2008;Shi et al 2008).…”