Bio-acidification of wines by Lachancea thermotolerans

Abstract

Insufficient acidity in grapes from warm climates/vintages is commonly corrected through addition of tartaric acid during vinification, and less so with other organic acids. An alternative approach involves bio-acidification with the yeast Lachancea thermotolerans (LT) via lactic acid production during fermentation. Our work first elucidated the genetic (~200) and phenotypic (~100) diversity of LT strains, and then tested the performance of their subset in co-cultures with Saccharomyces cerevisiae (SC). In pure and mixed cultures alike, the modulation of acidity and other compositional parameters of wines depended on the LT strain, with either comparable or significant acidification relative to the SC control. An LT strain with exceptional bio-acidifying properties was selected, capable of lowering wine pH by ~0.5 units, and further characterised across a range of oenological conditions.

Our follow-up study aimed to i) compare the profiles of bio-acidified LT wines and acid-adjusted SC wines, and ii) evaluate the use of LT wines as blending components. For this purpose, high sugar/pH Merlot grapes were fermented with a sequential culture of LT and SC, and an SC monoculture. The aliquots of the SC control (pH 4) were acidified with either tartaric or lactic acid to the pH of the LT wine (pH 3.6), and the initial wines also blended in three proportions (1:3, 1:1, 3:1). Chemical analysis revealed major differences in a range of chemical parameters of wines (e.g. ethanol content, acidity parameters, volatile compounds, amino acids).  The compositional modulations 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 an identical initial matrix, lactic acid-adjusted SC wine had higher ‘red fruit’ flavour, and lower ‘hotness’, ‘bitterness’ and ‘body’ relative to tartaric acid-adjusted wine. This was driven by differences in ‘acidity’ perception, affected by titratable acidity (rather than pH) of wines. An inhibition of Brettanomyces bruxellensis growth was also observed in the bio-acidified LT wine and the lactic-acid adjusted SC wine. The profiles of blends were modulated depending on the proportion of the bio-acidified wine, thus highlighting the potential of this approach to boost ‘freshness’ and differentiate wine styles.