Determination of anion and cation concentrations in West Texas grapes

The decline of the Texas oil and agriculture industries has shown the need for the diversification of the Texas economy in order to expand the income base for the state government and state supported services. Historically, Texas has been a center of wine production the Southwest and boasted a significant "cottage industry" of wineries. Unfortunately, this occupation virtually vanished during the early part of the twentieth century. The wine industry is now enjoylng a rebirth and it has become obvious that the technology applicable to wine production in California and France can not be relied on in Texas owing to the unique growing conditions encountered in the vrticultural regions of western and Southwest Texas.

As pH problems are a significant obstacle to the production of a commercially viable product, a integrated program of analysis to improve the understanding of the components involved in determining the pH of juice and wine was undertaken. Organic acid analysis was conducted by reversed phase HPLC while flame AA was used for the determination of metals. An ion exchange and subsequent titration method was used for gross charge determination. This method also served as a benchmark for comparison with the HPLC and AA methods. These techniques were used for monitoring changes in anion and cation content during maturation and vinlfication and for development of a simple method of calculating necessary corrections in acid levels of grape juice/ wine either by additions of tartaric acid or ion exchange.

Comparison of the summation of cations or anions to the gross charge titration on a percentage basis was used as an appraisal of the completeness of analysis. This idea of "charge balance" comparison was also used for direct comparison of the cationic and and anionic analysis.

In order to assess the degree of supersaturation of tartrate salts and to investigate the changes produced by acid additions to juices, several special treatments including chilling of juice, addition of acids and acid salts were performed on fresh juice samples. The results of these treatments were compared to wines after vinification.