Biological pH Reduction of Wine with the Use of Autochthonous Yeasts as Starter Cultures

Introduction: Wine preservation is an important necessity in winemaking and sulfur dioxide addition is thus considered indispensable. However, its use should be limited because of its negative effects on human health. 

Purpose: A biological method to reduce the pH and increase the total acidity of wines by the use of autochthonous yeast starters is presented, in order that bacterial spoilage management is reinforced.

Methods: Saccharomyces cerevisiae strains 21PW6 and 47PW1 were inoculated in pasteurized musts in mono-cultures (“mono”) or in mixed-cultures along with Lachancea thermotolerans strains 27PL4 and 16PL2, respectively. Two modes of inoculation were tested in mixed-cultures, i.e., sequential (“seq”) inoculation of L. thermotolerans followed by S. cerevisiae and simultaneous inoculation (“sim”) of both species.  Total acidity, pH, free and total SO₂, volatile acidity and major volatile compounds were determined and compared. 

Results: Ferments produced through “seq” fermentations showed the lowest pH values (3.24±0.00) compared to “sim” (3.41±0.03) or “mono” (3.51±0.13). Total acidity was significantly increased in “sim” (8.39± g of tartaric acid /L), “mono” (7.06± g of tartaric acid /L), and at much higher levels in “seq” (15.24± g of tartaric acid /L). Differences were also detected in the major volatile compounds of the ferments. The presence of L. thermotolerans strains in fermentations altered the pH, total acidity, and volatile acidity of ferments, while its dominance in “seq” fermentations revealed its ability to strongly influence these parameters.

Significance: Here we present an inoculation protocol with L. thermotolerans strains which can significantly lower the pH value and raise the total acidity of wines. We anticipate its use as an alternative preservation tool in winemakers’ hands, towards the production of safer wines with fewer additives.