All acids are equal, but some acids are more equal than others: (bio)acidification of wines

Abstract

Insufficient acidity in grapes from warm(ing) climates is commonly corrected through addition of tartaric acid during vinification, and less so with other organic acids. One alternative approach involves bio-acidification with certain strains of Lachancea thermotolerans (LT) via lactic acid production during fermentation. Our previous work delivered a superior LT starter capable of lowering wine pH by ~0.5 units when used in co-cultures with Saccharomyces cerevisiae (SC).  Here, we aimed to i) compare the profiles of the bio-acidified LT wines and the acid-adjusted SC wines, and ii) evaluate the use of LT wines as blending components. For this purpose, high sugar/pH Merlot grapes (14.5 ° Bé; pH 3.9) were fermented with a sequential culture of LT and SC, and an SC monoculture control. The two obtained wines blended in three proportions (1:3, 1:1, 3:1), and the aliquots of the SC control (pH 4) were also acidified with either tartaric or lactic acid to the pH of the LT wine (pH 3.5).  Chemical analysis revealed major differences in a range of compositional parameters, which were reflected in the sensory profiles of wines, as confirmed via ‘Rate-All-That-Apply’ evaluation by wine experts (n=30). Sensory profiles of the bio-acidified LT wine and the lactic acid-adjusted SC wine were similar, and contrasting to the tartaric acid-adjusted SC wine. Despite the identical initial matrix, adjustment with lactic acid resulted in intenser ‘red fruit’ flavour, and lower ‘hotness’, ‘bitterness’ and ‘body’ relative to the adjustment with tartaric acid, driven by increases in ‘sourness’. The profiles of blends were modulated depending on the proportion of the bio-acidified wine, thus highlighting the potential of this approach to fine-tune ‘freshness’ and differentiate wine styles.