Both during the production of process water as well as during the purification of industrial waste water, it is sometimes necessary to remove some or substantially all ions from the water. This is possible with a separation technique such as ion exchange. With this technique very low residual concentrations of ions in the treated water can be obtained. As the name describes during this process ions from the treated water are exchanged to harmless counter-ions such as Na, H, Cl- or OH-. Determined by the choice of the material selected the exchange can be done selective or not selective. Once the capacity of the ion exchanger is saturated it is regenerated with a concentrated solution of counterions.
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The use of cation exchange resins in wines: Effects on pH, tartrate stability, and metal content. School of Agricultural Sciences. 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 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, ; Boulton et al. 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.
Another winemaking issue that is closely linked with the acidity of wines is the development of insoluble salts, resulting from the reaction of anionic tartrates and cations such as potassium or calcium i. 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.
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.
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, ; Benitez et al. 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. 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, ; Mira et al.
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.
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, 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.
ACS reagent 98— The following trials were performed to evaluate the effects of using different volumes and concentrations of sulfuric acid during the activation of resins: three fritted columns, representing three replications, were loaded with Once the resins were activated and rinsed with 10 mL of distilled water, the columns were loaded with mL of Sauvignon Blanc or Petit Verdot wine samples Table 1.
To avoid sample contamination with sulfuric acid, the first 30 mL of treated wine was discarded. Finally, the flow of wine passing through the resin was regulated to approximately The pH of the different wine fractions was measured every 10 mL until mL of treated wine was collected. Wine samples of the varieties Sauvignon Blanc, Chardonnay, Merlot, and Cabernet Sauvignon Table 1 were subjected to a laboratory-scale resin treatment as explained before resin activation protocol.
As indicated before, all treatments were replicated three times, and the wines were analyzed for pH, total acidity, and metal content, as detailed below. As an extra precautionary measure, the first L of each wine batch were discarded to ensure the elimination of water and acid present from the previous steps. As indicated before, 10, L of wine was treated per exchange cycle, initiating with the white varieties and making sure that the resins were cleaned and regenerated before a new batch of wine was treated.
In this case, in addition to the analyses of pH, total acidity, and metal content, the number of samples available allowed us to evaluate the formation of tartrates in the treated wines. As before, all the treatments were replicated three times. General wine analyses: Alcohol concentration, pH, titratable acidity, volatile acidity, reducing sugars, free and total SO 2 , and electrical conductivity were done following the official protocols described elsewhere OIV, Moreover, calibration curves were prepared from standard solutions of each metal resulting in coefficients of determinations above 0.
Once digested, the samples were diluted to 50 mL with ultra-pure water and each wine sample was analyzed three times. One hundred mL samples were placed in mL beakers, to which 0. To quantify the mass of the tartrate crystals formed, the wine was filtered using nitrocellulose membrane discs 0. The mass of the tartrates formed was obtained by the difference between the final weight minus the mass of the membrane discs and the 0.
The samples that showed the formation of crystalline deposits that did not re-dissolve once the temperature of the wine warmed up to room temperature were considered unstable. This qualitative test was chosen as a quick way to estimate tartrate stability and supplement the results of tartrate formation measured by weight. The statistical analyses were performed using the free software R, version 3.
As indicated before, the volume of the resin base was fixed to 10 mL to allow the treatment of at least mL of wine. To avoid contamination of the sample with sulfuric acid, the first 30 mL of treated wine i. The results obtained for both wine varieties were consistent, showing that higher volumes or concentrations of sulfuric acid resulted in wines with lower pH.
Moreover, in most cases, the initial pH of the treated wines remained stable for at least 5 volumes of treated wine i. Regardless, the pH of the treated wines remained well below that of the untreated samples.
The former is an indication that the exchange capacity of the resins should be periodically checked to avoid significant efficiency losses by, for example, continuous monitoring of the pH of the wine being treated. During these trials, we also evaluated whether a varying flow of wine through the column influences the results, but no differences were found among wine flows between The cation exchange treatments significantly reduced the pH, increased the acidity, and lowered the content of most metals analyzed Table 2.
These results are in agreement with those obtained at a winery-scale Table 3 , as detailed and discussed in the following section. Rows with different letters are significantly different.
In agreement with previous reports Mira et al. For instance, treatment T3 i. Instead, treatment T4 showed conductivity values even higher than the untreated samples, even though they contained significantly less cations Table 3. The initial decrease in conductivity is consistent with a lower number of cations conducting electricity, as the proportion of resin-treated wine increases.
Given that the measurements of electrical conductivity were proven unsatisfactory as a way to estimate tartrate stability, the formation of tartrates was evaluated by weight. In the case of treatment T3 i. Additionally, former reports have shown that resin-treated wines may have a slight negative effect on the color of red wines but without a significant influence on their sensorial evaluation Lasanta, ; Mira et al.
The observed reduction in the amount of potassium i. Calcium tartrate CaT is less common than KHT but generates concern among winemakers, as it is not easily removed during cold stabilization. In this case, the K content in the untreated wines was within a normal range, with average values between and mg L As such, the average Ca content in industrial samples was between 40 and 60 mg L -1 , an amount below the range in which this type of instability has been observed to occur naturally i.
Moreover, the lower pH of the resin-treated samples would favor the equilibrium of the protonated and monovalent forms of tartrate, instead of the divalent form T 2- required for CaT formation Waterhouse et al.
Future studies should include sensory evaluations and assessments of the effects of cation exchange treatments on the aging capacity of the treated wines. To date, there is a growing amount of evidence demonstrating the essential role that metal ions play in wine oxidation. Trace levels of transition metals, such as iron and copper, are ubiquitous in wine and have been shown to serve as catalysts of oxidation. Therefore, it seems feasible to think that a technology capable of lowering the concentration of these metals may have an effect on the rate of wine oxidation.
Similarly, lowering the pH of wine could help reduce the oxidation reaction rate, improve the color expression in red wines, and help minimize the content of sulfur dioxide required for microbial activity and oxidation Boulton et al. The main conclusions are as follows: cation exchange resins proved to be an effective tool to reduce the pH, increase the total acidity, improve the tartrate stability, and decrease the concentration of a number of cations in the treated samples.
The effectiveness of the process varied according to the chemical composition of the wine to be treated and the operating conditions of the equipment. Bartowsky, E. Bacterial spoilage of wine and approaches to minimize it. Castro, and C. Removal of iron, copper and manganese from white wines through ion exchange techniques: effects on their organoleptic characteristics and susceptibility to browning. Acta — Bindon, K. Varela, J. Kennedy, H. Holt, and M. Relationships between harvest time and wine composition in Vitis vinifera L.
Cabernet Sauvignon 1. Grape and wine chemistry. Food Chem — Bordeu, E. Boulton, R. Singleton, L. Bisson, and R. Principles and Practices of Winemaking. Climate change associated effects on grape and wine quality and production.
Food Res. Esau, P. Synthetic ion-exchange resins in wine research. Industrial development of proton exchange for tartrate stabilization of sherry wines. Hannah, L. Roehrdanz, M. Ikegami, A. Shepard, M. Shaw, G. Tabor, L. Zhi, P.
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The use of cation exchange resins in wines: Effects on pH, tartrate stability, and metal content. School of Agricultural Sciences. 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.
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