Winetech Technical Yearbook 2022

SEPTEMBER

Steering away from flat and flabby Merlot

A COMPREHENSIVE STUDY INVESTIGATED THE POTENTIAL OF LACHANCEA THERMOTOLERANS AS A VALUABLE TOOL TO PRODUCE QUALITY WINES IN SITUATIONS WHERE MUSTS HAVE HIGH SUGAR AND LOW ACID CONTENT.

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BY CARIEN COETZEE

INTRODUCTION Merlot is known for its supple texture and ripe fruit flavours, however, it can be a challenging variety to work with as it is known for high sugar and low to medium acidity musts, especially in warmer grape-growing climates. 1 Its tendency to overripen in warm areas is further exacerbated through accelerated phenological development in the context of climate change. 2 Consequently, Merlot wines often contain overly high ethanol levels, but lack acidity. Optimal harvest timing is critical when working wi th Mer lot , and winemakers often adjust their grape growing and winemaking regimes to try and minimise the potential alcohol content and improve the acidity. These interventions can be costly, complicated and detrimental for wine quality and sensory perception. A specific yeast strain, Lachancea

metabolites and the sensory rating by wine experts. Only the main findings of the study will be reported in this article. Lachancea thermotolerans capabilities Before we dive into the main findings of the above-mentioned study, it is important to understand the advantages and properties of LT yeast in winemaking: • Acidifier The major metabolic contribution of LT is the partial conversion of sugars to lactic acid (as opposed to ethanol) during alcoholic fermentation. LT yeast is extremely efficient in converting sugars to lactic acid: the maximum reported concentration of lactic acid formed during LT wine fermentation is 16.6 g/L. 7 By comparison, Saccharomyces cerevisiae yeasts produce very little, if any lactic acid. 8 The advantage of lactic acid is that it is an effective acidulant and it is stable (physiochemically and microbially), while other permitted acidulants might not be. 6 • Lowers the alcohol content Depending on the strain and the conditions, reports describe either similar or about 1% v/v lower ethanol concentrations in wines co-fermented with LT compared to their respective Saccharomyces cerevisiae fermentations. 9-12 • Other properties Other compositional alterations in LT wines include increases in glycerol, decreases in acetic acid and partial degradation of malic acid. 10, 11, 13-18 LT contributes to the production of wines with enhanced mouthfeel, floral notes, fruitiness and freshness. 19 MATERIALS AND METHODS Merlot grapes (high sugar/low acidity) were handpicked from Australian vineyards during the 2019 vintage. Juice analyses

thermotolerans (LT), is an acidifying, lower ethanol yielding yeast and is, therefore, a fitting solution for the high sugar/ low acidity conundrum. This yeast is naturally found on grapes and in wines and has been investigated for its application in oenology for many years already. 3,4 A comprehensive study 5 aimed to determine the performance of five LT strains using Merlot musts with high sugar/low acidity content compared to control treatments. The fermentation performance, as well as the chemical and sensory analyses, of the various treatments were reported. The original publication focussed on the extent of acidification, the production of primary and secondary

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WINETECH TECHNICAL YEARBOOK 2022