The fermentation of grape must is a complex process involving the development of different microbial species. The use of selected starter cultures to drive said fermentation is now practiced in most wine regions of the world, and the range of commercially available microorganisms has been expanding over the years, giving wine producers the ability to rationally manage various aspects of guided fermentations. At the same time, increased consumer attention to sustainability and economic cost pressures are driving wine producers to seek methods to reduce environmental impact during production.
In this context, the exploitation of microorganisms to make winemaking more sustainable is a recent and still under-researched approach. Indeed, in the past, sustainability in viticulture was mainly understood as reducing the use of pesticides, fertilizers and heavy metals in the vineyard. However, recent studies have shown that the environmental impact of wine also depends on the stages of winemaking, including the microbial transformations that occur during winemaking.
In recent years, in fact, new potentials of fermentation steps have been discovered to improve the environmental impact and CO2 emissions associated with winemaking, as summarized in Figure 1. These include among others the reduction of sulfites (through, for example, bioprotection), increased biodiversity (through the inoculation of non-Saccharomyces yeasts), and energy savings associated with fermentations, particularly alcoholic fermentation.
In fact, most of the electricity used by wineries (about 90 percent) is consumed by refrigeration systems for fermentation control, cold stabilization and storage of musts and wines.
In the production of white and rosé wines, the fermentation process occurs, for quality purposes, at a controlled temperature, at which the wine must be cooled at the beginning of fermentation and throughout the process; and the fermentation reaction generates heat that must be removed. Overall, however, some recent studies show that significant energy savings can be achieved through temperature management of fermentations, that is, avoiding excessive refrigeration when unnecessary, without compromising the sensory quality of the wine.
From the microbiological point of view, The scientific literature has already extensively described the effect of temperature on yeast metabolism during wine fermentation.
In the past, it was believed, in particular, that only at low temperatures a high amount of aromas were produced. However, recent studies have shown that this is not always true. The results in the bibliography are numerous and not always in agreement with each other. In fact, in recent years it has been recognized that the effect of low temperature on aroma production by yeasts varies greatly depending on the strain of Saccharomyces cerevisiae. This is easily understood when considering the conditions under which different researchers conducted their trials. The yeast strains used are varied, as are the flavor families analyzed and the must conditions employed (strain, sugars, assimilable nitrogen, sometimes even synthetic must). In addition, the temperatures compared with each other in each scientific work show rather large differences: the laboratory studies deliberately “test” the yeast in extreme model situations, going, for example, from 12 to 25 °C, or from 15 to 28 °C, or even from 10 to 20 °C, variations that no oenologist would make in the cellar in a white wine making process.
So, the effect of temperature on aroma production by yeasts is complex and depends on several factors.
Considering this starting point, there was and is, therefore, room to study the effect of a reasoned increase in fermentation temperatures in order to save energy in the cellar, without jeopardizing the winemaking result. Accordingly, several experiments have been conducted in recent years to quantify the energy savings that can be achieved in white winemaking (sparkling wine bases or still wines) by increasing the fermentation temperature by 3-4 °C compared to the usual protocol.
In a first study conducted in 2016 by CREA in collaboration with the University of Milan, the effect of fermentation temperature on the production of Chardonnay sparkling wine base was tested.
Fermentation was conducted at a temperature 4°C higher than the winery standard, namely 19°C instead of 15°C. The results showed that increasing the temperature produced energy savings of about 65 percent without compromising wine quality. In particular, no significant differences were found in the main chemical parameters of the wine, nor in sensory characteristics (triangular test with forced choice).
In another study conducted in 2019 by a research group in Germany, the effect of fermentation temperature on Riesling base wine production was tested by comparing fermentations at 19°C, 17°C and 14°C.
The results confirmed those of the previous study, showing that increasing the temperature produced energy savings of about 70 percent with the 5°C increase, without compromising wine quality. Finally, a third study was conducted on an industrial scale at larger volumes by the CREA – University of Milan group, and recently published, to give robustness and confirmation to the previously acquired data. In this study, conducted in 2019 and 2020, grapes of Glera and Pinot Grigio varieties were used, musts were fermented in 450 hL tanks, energy savings varied in this case between 30 and 35 %, again with confirmed oenological and sensory results.
In conclusion, the data from the reported studies show that the use of appropriately chosen selected yeasts and properly reasoned fermentation protocols can provide significant energy savings in white wine making without compromising wine quality.
Further development of ongoing research will be needed to give winemakers adequate tools in this regard. Interest in this line of research is, moreover, also appreciable in the international context, as evidenced, for example, by the fact that the OIV, International Organization of Vine and Wine, has included the study of energy conservation in the fermentation process among the topics of its Research Grants, which are in turn hinged on the topics of priority programs.
From OICCE Times Rivista di Enologia No. 97 – WINTER 2023, pp.54-56, Rubrica di Microbiologia
Valentina Giovenzana, Roberto Beghi, Ileana Vigentini, Riccardo Guidetti and Tiziana Nardi (2023) “Impact of fermentation-temperature management combined with specific yeast choice on energy savings in white winemaking”, BIO Web Conf., 68 – 02035. doi.org/10.1051/bioconf/20236802035
Giovenzana, V., Beghi, R., Guidetti, R., Luison, M. and Nardi, T. (2023) “Evaluation of energy savings in white winemaking: impact of temperature management combined with specific yeasts choice on required heat dissipation during industrial-scale fermentation”, Journal of Agricultural Engineering, 54(3). doi: 10.4081/jae.2023.1523.
Valentina Giovenzana, Roberto Beghi, Paola Vagnoli, Francesco Iacono, Riccardo Guidetti, Tiziana Nardi (2016) “Evaluation of Energy Saving Using a New Yeast Combined with Temperature Management in Sparkling Base Wine Fermentation”. Am J Enol Vitic. 67:308-314 ;DOI: 10.5344/ajev.2016.15115