2.4.2. Enological Parameters

The quantitative determination of these parameters was carried out following the guidelines of the official methods published in Boletín Oficial del Estado (BOE) number 1988-11256 and the International Organization of Vine and Wine (OIV).

The ethanol content of the samples was determined by near infrared (NIR, Anton Paar; Camino de la Fuente de la Mora, 9, 28050 Madrid, Spain) equipment. The values of pH and total acidity were determined by pH apparatus coupled to an automatic titrator (Mettler-Toledo S.A.E. Miguel Hernández 69-71, 08908 Hospitalet de Llobregat, Barcelona, Spain; 2000 series) calibrated according to certified standards. The parameters referring to the colorant composition of the samples were measured by spectrophotometric techniques using Lan Optics equipment (series 2000).

The amounts of free and total sulfur dioxide were analyzed by steam trawling following the Franz Paul approach and distilling equipment supplied by GAB Technologies. The determination of organic acids and sugar content (glucose + fructose) was based on automated enzymatic methods with measurement by spectrophotometry using enzymatic equipment (Analyzer Y15, Byosistem, Barcelona, Spain). In the case of succinic acid, a manual enzymatic method was followed using the kit supplied

by Megazyme (https://www.megazyme.com/) through the generation of calibration and measurement lines by spectrophotometry with Lan Optics equipment (2000 series).

#### 2.4.3. Quantification of Metals

The quantitative determination of metals was made by means of the following methods. A prior digestion was conducted in sealed containers to mineralize the wine samples. The samples were subsequently analyzed by an optical emission spectrometer with excitation by induced argon plasma and a dispersive system as previously described [8]. For the realization of the calibration lines, solutions of each of the reference standard mediating elements supplied by Sigma Aldrich in 5% NO3H were prepared. The metal quantification analyses were carried out by the regional agricultural laboratory of La Grajera of the Government of La Rioja.
