The use of elicitors in viticulture: a tool to obtain highly colored wines with a reduce alcohol content?

Abstract

Context and purpose of the study

Climate change is causing a gap between the technological and phenolic maturity of grapes, resulting in wines with high alcohol content and low polyphenol concentration. Another phenomenon associated with high temperatures and whose effect is more pronounced if the harvest is delayed is the decrease in the acidity of the grapes, mainly in malic acid, and an increase in pH caused by the accumulation of potassium derived from the increase in temperature. Therefore, climate change and the effects it causes on the vine leads to unbalanced wines,  with high alcohol content and lack of color, with green tannins, astringency and excessively low acidity if not corrected.

The use of elicitors has been shown to lead to an increase in the concentration of polyphenols in grapes and given these observations, the objective of this work was to evaluate the efficacy of the foliar application of three different chemical elicitors (Lalvigne Mature, Harpin ab and Bion) to increase and accelerate the synthesis of phenolic compounds in the treated grapes, allowing harvesting them with less sugar and, therefore,  allowing obtaining i wines with less alcohol. 

Material and methods

The study has been carried out for three consecutive years (2019, 2020 and 2021) in a vineyard of ‘Monastrell’ grapes, located in the D.O. Jumilla (Murcia, Spain). Three different commercial elicitors were applied by foliar spray, Lalvigne Mature (yeast derivative, Lallemand), Harpin ab (a protein molecule that consists of four fragments from other harpin proteins found in bacterias that cause diseases in plants, Plant Health Care) and Bion (benzothiadiazole, Syngenta). In 2019 and 2020, two applications were made, at veraison and 15 days later. In 2021 only Harpin was applied and a third dose was added 15 days after the second foliar application.

Grapes from each treatment were vinified following a traditional red winemaking process and the physicochemical and chromatic parameters were analyzed at the time of bottling.

Results

The results show that treatment with elicitors can be an effective tool to alleviate the consequences of climate change in the enological sector, obtaining wines with 8-15% less alcohol, but with a polyphenol content similar or even greater than that of a wine made from control grapes without any treatment and similar to that obtain in wines from control grapes harvested with a higher ripening degree.

These results vary according to the elicitor used and the year of treatment and its climatological characteristics. The Harpin elicitor is the most consistent in its results year after year, being very effective when three treatments are applied to the grape separated from each other 15 days from each other (harvest of 2021). When this elicitor was applied, wines presented around 15% less alcohol than a wine made from the most ripen control grapes, and with similar chromatic parameters, even more polymeric anthocyanins were measured, which may help to the stability of the color in these wines.