XXIes ENTRETIENS SCIENTIFIQUES LALLEMAND : SENSORY DEVELOPMENT OF COOL-CLIMATE VARIETALS DURING WINE FERMENTATION
Montreal, MAY 3, 2009 – This year, the XXIièmes Entretiens Scientifiques Lallemand, held April 24, focused on cool-climate varietals and how to understand their sensory development, and the impact wine fermentation has on their properties. The meeting was held in collaboration with the Geisenheim Research Center, which celebrated the 115th anniversary of the Geisenheimer Hefe-Reinzucht-Station. The meeting gathered some of the top scientists in the field to present this topic to an international and local crowd. It was also an opportunity to hand out the Lallemand award to the most deserving student of the Geisenheim campus in the field of Wine Microbiology. Daniel Gerhards, an M.Sc. student, was the proud recipient of this award for his work “The investigation of the metacaspase YCA1 for better detection of apoptosis in Saccharomyces cerevisiae during alcoholic fermentation of grape must.”
Professor Manfred Grossmann, head of the section Microbiology and Biochemistry at the Geisenheim Research Center, opened the meeting with a comprehensive review of the diversity of current research at our host institution.
Dr. Chris Curtin, from the Australian Wine Research Institute, presented the first results of trials done on Chardonnay from the Margaret River, a relatively cool region in Western Australia, fermented with different yeasts, and how that would impact the production of specific sensory compounds, including thiols, and consumer preference. The results of his work show that different yeasts produced different concentrations of aroma compounds. Interestingly, the presence of thiols is important in this type of Chardonnay, and thiols are compounds typically associated with such varietals as Sauvignon Blanc. As it appeared the concentration of thiols could be related to the yeast activity, and as it was reflected in the consumer preference test, the choice of yeast is particularly important in order to respect the varietal typicity and the style of wine desired by the winemaker.
Based on the research done at the DLR Rheinpfalz, in Germany, in the laboratory of Ulrich Fischer, their study on yeast and its role in terroir expression was presented. Their preliminary work showed that terroir goes beyond individuality – it is all about recognizable typicality, related to unique vineyards or regions – and the winemaker influences it via viti-vinicultural decisions. In one experiment in Riesling from 2004, it appears that the “cellar yeast terroir” is more important than the “vineyard terroir,” which alone introduced no more sensory variation than the use of commercial yeast starter cultures.
Dr. Yves Le Fur, from the UMR FLAVIC, INRA-ENESAD – Université de Bourgogne group, echoed some of the same sentiment regarding terroir expression when he presented their work on the definition of the unique sensory space of Chardonnay wines by wine experts, by having wines defined by exemplary scores. The next step consisted of determining whether the physicochemical analysis of the volatile compounds present in the wines could account for the wine exemplarity scores. The relative concentrations of 35 volatile compounds were shown to play a role in the wines’ exemplarity scores. Their results emphasize the complexity of the odour quality of Chardonnay wines, with some volatile compounds stable across vintages, while others are vintage specific.
From the perspective of malolactic fermentation (MLF), Ramón Mira de Orduña, from Cornell University, presented on acetaldehyde, which is a small and highly reactive molecule which has chemical, sensory and microbiological significance in wine, although lately there has been controversy regarding its negative impact on human health. Acetaldehyde contributes to red wine colour development and stability. However, the aroma of excessive acetaldehyde is undesirable, as is its affinity to bind SO2, which becomes even more critical with regard to the common trend to lower total SO2 concentration in wine. The studies of the group demonstrated that oenological lactic acid bacteria play an essential role in removing acetaldehyde from wine. The degradation of acetaldehyde follows the same pattern as the degradation of malic acid, with little delay (two to five days). Thus, MLF helps reduce the total SO2 needs of wine.
MLF was also the focus of Tatjana Košmerl, from the University of Ljubljana in Slovenia. The work of her team showed that the use of different lactic acid bacteria starters not only had an impact on the course of MLF in Welsh Riesling and Sauvignon, but on their chemical composition as well. She concluded that induced MLF has proven to be the recommended method for improving wine quality, and that the contribution of MLF was higher in white wines from cooler winegrowing regions.
The sensory impact of yeast and bacteria are now established facts, and ongoing research results allow us to understand the mechanisms behind those processes, so that winemakers can benefit from this information. The prime goal of our investment in research is to translate scientific results into improvements in wine quality, and our association with the Geisenheim Research Center for this event reflects this cooperative spirit.
ABOUT THE FORSCHUNGSANSTALT GEISENHEIM The Forschungsanstalt Geisenheim (Geisenheim Research Center) in Germany conducts primarily applied research serving the development of wine and beverage industries, as well as the industries related to indoor and outdoor horticulture. The section Microbiology and Biochemistry concentrates on specific research topics concerning wine yeasts and bacteria. This includes as key missions the elucidation of interactions between wine relevant microorganisms and important metabolic pathways in order to bring more light into the presence of quality determining compounds which are produced during alcoholic and malolactic fermentations or during any other step of the wine making process. As consequence of the long history of the section and driven by latest technical developments, a broad range of microbiological, molecular biological and chemical analytical equipment and methods are applied.