The use of cation exchange resins in wines: Effects on pH, tartrate stability, and metal content

Cien. Inv. Agr. 45(1):82-92. 2018 www.rcia.uc.cl viticulture and enology DOI 10.7764/rcia.v45i1.1911 research paper The use of cation exchange resins in wines: Effects on pH, tartrate stability, and metal content Felipe Ponce1, Yaneris Mirabal-Gallardo2, Andrea Versari3, and V. Felipe Laurie1 1 Universidad de Talca. School of Agricultural Sciences. 2 Norte 685, Talca, Chile. Institute of Applied Chemistry, Faculty of Engineering, Universidad Autónoma de Chile. 5 Poniente 1670, Talca, Chile. 3 Department of Agricultural and Food Sciences, University of Bologna, Piazza Goidanich 60, 47521 Cesena (FC), Italy. 2 Abstract F. Ponce, Y. Mirabal-Gallardo, A. Versari, and V.F. Laurie. 2018. The use of cation exchange resins in wines: Effects on pH, tartrate stability, and metal content. Cien. Inv. Agr. 45(1): 82-92. Treating wines with cation exchange resins allows the reduction of pH and contributes to limiting the formation of tartrate salts by exchanging cations such as potassium with hydrogen ions. This manuscript summarizes the results of a series of laboratory and winery-scale trials performed with the aim of evaluating the ion exchange process and its effects on the chemical composition of the treated samples. The laboratory-scale results showed that both the procedure employed for the activation of resins and the chemical composition of the wines affected the extent of the chemical changes occurring during the treatment. As such, the winery-scale trials showed that the resin-treated wines have significantly lower pH, higher total acidity, less tartrate formation (measured by weight), and a reduced amount of most metals analyzed. Wine samples blended with approximately 20% of cation exchange-treated samples (by volume) showed no signs of tartrate instability when assessed by a quick qualitative cold test. Keywords: Ion exchange resins, metals, pH, tartrate stability, wine. Introduction Wine pH has a remarkable effect on the quality of the final product, influencing its chemical, microbial and sensorial stability. High pH wines are less tolerant to microbial spoilage, in need of higher amounts of sulfites, less stable aromatically, and have a diminished potential shelf life (Bartowsky, 2009; Boulton et al., 1996; de Orduña, 2010). Nevertheless, high pH wines are not uncommon, as some producers prefer to work with ripened fruit as a way to avoid certain vegetal nuances and the characteristic astringency of less mature grapes (Bindon et al., 2013; Romero et al., 2006). Likewise, the establishment of short-cycle grape varieties in warm areas and the rising temperatures of some viticultural regions could be exacerbating the occurrence of high pH wines (de Orduña et al., 2010; Hannah et al., 2013; Webb et al., 2012). Received Dec 14, 2017. Accepted Mar 06, 2018. Corresponding author: Another winemaking issue that is closely linked with the acidity of wines is the development of VOLUME 45 Nº1 JANUARY – APRIL 2018 insoluble salts, resulting from the reaction of anionic tartrates and cations such as potassium or calcium (i.e., potassium bitartrate, KHT, or calcium tartrate, CaT) (Boulton et al., 2006; Ibeas et al., 2015). The concentration of these cations in wines may be as variable as 125–2040 mg L-1 for K+, and 50–300 mg L-1 for Ca2+ (Ough et al., 1982; Pohl, 2007; Laurie et al., 2010), and their upper concentration range represents a higher risk of tartrate salts formation. If this phenomenon is not addressed during winemaking, these crystals may appear as deposits at the bottom of the bottles, thus possibly causing consumer rejection (Boulton et al., 2006). In regard to solving these issues, the lowering of wine pH is most typically performed by the addition of tartaric acid, unless titratable acidity is high. Instead, preventative solutions to avoid tartrate precipitation in commercial wines range from the use of chemicals to physical means such as cold stabilization (Boulton et al., 2006; Mira et al., 2006). One of the alternatives available to simultaneously lower the pH, reduce the concentration of cations, and limit the formation of tartrate salts is the use of cation exchange resins (Bordeu and Cristi, 2001; Benitez et al., 2002; Mira et al., 2006; Lasanta et al., 2013; Ibeas et al., 2015). These substances are comprised of a polymeric matrix onto which different ionized functional groups could be attached, depending on the type of exchange required (i.e., carboxylic acid or sulfonic acid for acidic resins and various types of amino groups for basic exchangers) (Esau and Amerine, 1966; Mira et al., 2006). These charged functional groups are neutralized by ions of the opposite sign that can be exchanged for ions of equivalent charge present in the treated samples (Esau and Amerine, 1966; Mira et al., 2006; Boulton et al., 2006). In conventional wine treatment, the resin beads are activated with a strong acid solution such as sulfuric or hydrochloric acid, rinsed with soft water, and loaded with the sample to be treated. As the wine is passed through the column, the hydrogen ions (H+) loaded onto the resins are exchanged by wine cations, such as 83 potassium or calcium (K+, Ca2+), thus causing a reduction of wine pH, cation concentration, and a reduced likelihood of the formation of tartrate salts (Palacios et al., 2001; Walker et al., 2002; Benitez et al., 2002; Mira et al., 2006; Lasanta et al., 2013; Ibeas et al., 2015). According to the regulations of the International Organization of Vine and Wine, OIV, cation exchange treatments must not alter the nature of the wine and should avoid significant reductions in color intensity, metallic content (>300 mg L -1), and pH (should remain above 3.0 and its total decrease should not exceed 0.3 units). The treatment must not leave foreign substances in the wine or impart characteristics that are unusual; and when used for acidification, this should not increase more than 54 meq L -1 (OIV, 2016 a-c). Given that the chemical composition of the wine samples and the operating conditions of the equipment may vary widely, we developed a series of laboratory and commercial-scale trials with the aims of testing the ion exchange process and evaluating its effects on the pH, metal content, and formation of tartrate salts on the resulting wines. Materials and methods Reagents and materials Laboratory-scale treatments were done using the “ion exchanger I” (Reag. pH Eur., Merck, Darmstadt, Germany), three fritted columns (length: 24 cm; diameter: 4 cm; frit pore size: 40–100 μm; stopcock bore size: 4 mm; stopcock plug size: 15.2/30 mm), sulfuric acid (95–97% p.a., Emsure®, Merck), and ultra-pure water (Millipore, Darmstadt, Germany). Additionally, commercial-scale trials were conducted in a Juclas-Vason MMPH2013 system (Verona, Italy) equipped with a proprietary defined cationic resin, using 50% sulfuric acid (Proquiel, 84 CIENCIA E INVESTIGACIÓN AGRARIA Santiago, Chile), and softened water produced on site (<45 ppm CaC (...truncated)