Foliar kaolin residues in grapes and its influence on the alcoholic fermentation process

Abstract

Kaolin is increasingly used in Mediterranean viticulture as a foliar particle film to mitigate heat and water stress and to control grape leafhoppers. The residues of kaolin foliar application on musts and wines, and their effect on alcoholic fermentation, is still poorly documented.

This work evaluates the effect of different foliar kaolin experiment application in commercial vineyards from three zones of the province of Valencia (Spain) in six grape varieties (Chardonnay, Muscat, Monastrell, Tempranillo, Marselan, Garnache). Five treatments were tested in a randomized block design. Control and four different kaolin applications (combining 5 – 10% v/v. and one or two applications pre- and/or post-veraison). Microvinifiations were carried out at pilot scale in stain-steel tanks of 50 L. Metal content was quantified by ICP-OES in musts and wines. The effect of kaolin on fermentation kinetics was evaluated at laboratory scale from Tempranillo and Monastrell must, fermented by four commercial yeast strains. Fermentation kinetics were modelled from weight-loss curves using a re-parametrized Gompertz equation, and kinetic parameters and metabolite profiles (HPLC and GC) were analysed with linear mixed-effects models and multivariate approaches.

Kaolin strongly increased aluminium concentrations in grapes reaching up to 400 mg/L in Chardonnay. However, Al content decreased sharply during winemaking. Regarding alcoholic fermentation, it seems that kaolin residues do not have a relevant effect on the development of the fermentation process. All the wines (treated and control) concluded the alcoholic fermentation without delay or stuck fermentation.

To conclude, foliar kaolin can be integrated into vineyard management without compromising fermentative behaviour. Nevertheless, aluminium content in grapes should be considered when assessing food safety. Further studies should be performed to evaluate kaolin residues in other phases of the winemaking process and final wine composition.

Funding

Grupo Operativo Supraautonómico GO-UBAVIDA. Estrategias sostenibles del viñedo a la bodega para la obtención de Uva de Baja concentración de Azúcares y Vino DesAlcoholizado. Financia: Ministerio de Agricultura, Pesca y Alimentación (MAPA) y (FEADER). Participantes: FEUGA, Bodegas Enguera, Bodegas Paco y Lola, Bodegas Matarromera, CIAL-CSIC, VITEC, FEV, PTV.

AQ and LP-T acknowledge the award of the Spanish government MCIN/AEI to the IATA-CSIC as Center of Excellence Accreditation Severo Ochoa (CEX2021-001189-S/ MCIN/AEI / 10.13039/501100011033).

Raul Ferrer Gallego thanks the funding of MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR (RYC2021-031638-I) and CNS2023-14445.