The problem of the increasing pH in sparkling wines caused by climate change: use of cationic exchange to correct it

Introduction

In recent years, the increase in temperature and the changes in rainfall distribution caused by climate change are affecting vine and grape physiology and are consequently impacting wine composition and quality (Schultz, 2000; Jones et al., 2005). As a consequence of global warming, the grape pulp ripens faster, and the pH and sugar concentration become too high and titratable acidity too low (Schultz, 2016). Therefore, grapes reach a very high potential alcoholic degree and pH sooner than usual. This phenomenon causes harvest dates to be earlier and makes it much more difficult to pinpoint proper aromatic and pulp maturity, which leads to unbalanced wines (Zamora, 2014). The increase on the pH is especially problematic in sparkling wines because they need higher acidity to maintain an adequate freshness.

In this new scenario, oenologists are looking for strategies to mitigate these effects. There seems to be only two possibilities: they can harvest when alcoholic degree and pH are at the correct level and accept that the grapes will not have the correct aromatic and phenolic maturity; or they can wait for adequate maturity and accept that the wines will have high ethanol content and pH.

Neither of these choices is conducive to obtain high quality wines and therefore winemakers are obviously concerned about this problem. Since the lack of real grape maturity cannot be compensated for, most winemakers prefer to wait for the correct grape maturity and then later apply procedures to compensate for the disequilibrium of these unbalanced grapes (Zamora, 2014).

Several practices for reducing sugar in grape juice or ethanol in wines have been proposed (Zamora, 2016). More problematic is compensating titratable acidity and pH. The problem of the low titratable acidity of grape juices and wines can be easily solved by adding authorised acids. Nevertheless, all these organic are not efficient enough for lowering the pH. Furthermore, the use of mineral acids is strictly forbidden (OIV, 2021). In fact, there are only two techniques authorised by OIV for reducing pH: electrodialysis and cationic exchange. Both techniques are very effective and are being increasingly used by wineries; however, cation exchange is probably being more widely used due to its lower cost (Lasanta and Gómez, 2012).

Several studies have been reported about the use of cationic exchange in grape juice and wine and its effects on wine composition and quality but only few of them refer to base wines and only one of them have focused on the effect on sparkling wines produced using the traditional method (Just-Borras et al., 2022). Therefore, the aim of this work is to study how applying cationic exchange to the grape juice influences the composition and quality of the base wines and their corresponding sparkling wines.