Introduction effect of moisture losses. Depending on the particular climatic conditions of the year, the raisining process
1. Introduction effect of moisture losses. Depending on the particular climatic conditions of the year, the raisining process
Among the European sweet wines, the Pedro takes 5-7 days, but it can be as long as 10 days under Ximenez sweet wine (P.X.) is increasingly recognized especially unfavorable circumstances. worldwide, causing its annual production to be This traditional drying presents several problems virtually sold in advance. P.X. wines are obtained from such as insect attacks, intense solar radiation, white grapes of the same name that are subjected to a occasional rains and fungi producing toxins, like traditional sun-drying process in order to raisin the ochratoxin A (OTA), which would need a strict berries. Grapes are harvested at the end of August and sanitary control of grapes to make quality wines. These the first days of September with approximately can deteriorate grapes during sun-drying. Thereby, the
14 ºBaume and the bunches spread onto long stripes of replacement of the traditional sun-drying process of
a plastic material placed on grounds with mild slopes Pedro Ximenez grapes for chamber drying under facing south in order to facilitate slow raisining by the controlled conditions should be advantageous because
Corresponding author: María P. Serratosa, Ph.D., acting of its non-dependency on the climatic conditions. This professor, research fields: chemistry and biological engineering.
method with controlled temperature is reliable, fast and E-mail: mpserratosa@uco.es.
Differences in Browning Index and CIELAB Coordinates of the Two Grape Drying Processes, Traditional 975
Sun-Drying and Chamber-Drying and during the Ageing of Pedro Ximenez Sweet Wine
easy to use, but it requires high efficiency to be
Wine of the year
profitable. The brown color of raisins is the combined result of
rd
pigments formed by the effect of the enzymatic and non-enzymatic reactions [1], taking place during grape
dehydration [2]. Oxidative enzymes such as polyphenoloxidase (PPO) [3] catalyze the oxidation of
1 st criadera
phenolic compounds to quinones in the presence of
molecular oxygen, which subsequently evolve to
solera
brown pigments (melanins). Also, exposure of berries to high temperatures (above 50 °C) can result in the
formation of melanoidins, which are brown polymers typically appearing in the last stages of the Maillard
reaction [4]. In addition, oxidative aging in wood
induces major oxidation reactions of phenolic Fig. 1 Traditional oxidative aging made in South Spain.
compounds in wine [5], particularly those involving the The wine obtained with this traditional method is flavan-3-ol derivatives, which have proved to be
homogeneous, with a very dark brown color. effective substrates for several browning reactions [6, 7].
The purpose of this work was to examine changes in The winemaking of these wines is a special
color during the traditional sun-drying and the elaboration. The resulting raisins are crushed and
chamber-drying at a controlled temperature of Pedro pressed under high pressure in a vertical hydraulic
Ximenez grapes, which are largely used to produce press in order to ensure a yield of must of at least 30%
sweet wines of the same name. Likewise, changes in (weight/volume). The musts thus obtained are the color parameters during cellar aging compared with extremely sweet (they can easily contain reducing
commercial bottled wines were studied. sugar concentrations above 450 g/L), with a strong