For thousands of years, humans have been indulging in the pleasures of alcohol. It is one of the few pastimes that run throughout the history of civilisation. But what did wine taste like without the modern technologies we have today? In the modern day world, wine may be described as somewhat spicy, smelling of roasted walnuts, apples, toasted bread, and curry, with a very dry and sappy mouth feeling.
Romans would often add herbs, spices, honey, or saltwater before drinking the wine, to experiment with flavour and medicinal properties. As humans became more advanced in the production, storage, and fermentation of grapes, we created more delicate wines with sophisticated flavour profiles, aromas, and textures.
In the modern world of wine, terroir reigns supreme. This French term encapsulates the unique combination of soil, climate, and topography that imparts distinct characteristics to wine. These terroir factors affect many viticultural practices, such as fruit ripeness, maturation, and harvest dates, which have a direct impact on the quality of wine.
While much attention is given to the climate and grapes themselves, an equally critical yet often overlooked aspect of winemaking, is the role of microbial communities. Fermentation is at the heart of winemaking, where grape juice transforms into wine through the action of yeasts and lactic acid bacteria. These microorganisms are present within the grape must, the natural, freshly pressed grape juice.
The yeasts break down sugars to ethanol (alcoholic fermentation), which encourages lactic acid bacteria growth. These bacteria then begin the malolactic fermentation process, where they convert malic acid to lactic acid. Not only do these microorganisms liberate the aromas and flavour profile of the grapes, but they are the tiny soldiers that help give you a little, or large, buzz. So next time you drink a glass of wine or alcoholic beverage, give a toast to these yeasts and bacteria.
Many winemakers choose to select conventional, commercial strains of microbes for fermentation to ensure gold-standard wine, rather than risk the potential of rotten grape juice. Others opt for spontaneous fermentation, which relies on naturally occurring microorganisms on the skin of grapes or in the environment (air or soil). In such vineyards that use spontaneous fermentation, the diversity, abundance, and role of these microbes are crucial in the development and quality of the wine.
As climate change reshapes our environment, its impact on these microscopic winemakers becomes a fascinating field of study. Dr Aghogho Ohwofasa’s work explores the variation of microbial populations between different vintage years on the same block of a vineyard that consistently uses an organic approach.
Between vintage years and geographical regions, the climate, such as average temperature, relative humidity, and rainfall that a vineyard receives varies. Climatic variation influences the vintage effect, which is used to describe the variation in yield, quality, and typicality of both grapes and wine from year to year.
The purpose of Aghogho’s study was to figure out which climatic factors varied between the 2018 vintage and 2021 vintage and how that variation influenced the bacterial and fungal communities present. The first step was to select two areas of the vineyard for each vintage that had the same shared location and would experience the same weather.
Next, the microbial communities were compared between each vintage year. Samples were taken from the grape juice at four important fermentation time points. These were the start of fermentation, two times during the process of fermentation, and the end of fermentation. The detection of the yeasts and bacteria in the samples was achieved through metabarcoding, which is able to detect and sequence the DNA of all the organisms present in the sample.
The results from Aghogho’s study indicated that the diversity and abundance of bacterial and fungal communities varied between the 2018 and 2021 vintage years. The bacterial community and composition of the 2018 vintage had 56 genera (groups of species) that were uniquely present in that particular year and showcased much greater diversity when compared to the 2021 vintage, with only 17 genera.
In spontaneous wine fermentation, Saccharomyces yeast species typically predominate due to their specific adaptive traits, which give them competitive advantages over other yeast species. The graph below in Figure 6 shows that Saccharomyces yeasts made up 53% and 46% of the yeast species in 2018 and 2021 respectively.
Other dominant yeast species included Auerobasidium, Hanseniaspora, Stramerella, and Metschnikowia. Despite the dominance of Saccharomyces within the 2018 and 2020 vintage, there was variation between other yeast species, namely Stramerella (2018 vintage) and Metschnikowia (2021 vintage).
Inevitably each year, a batch of grapes will have a unique profile of microorganisms that influence the development of the wine. But since different yeasts unlock different aromas, what risks may vineyards be facing due to these changing populations?
The dominant lactic acid bacteria involved in winemaking include the Lactobacillus, Pediococcus, Leuconostoc, and Oenococcus genera. The activity of these bacteria can modify the wines appearance, flavour, aroma, and texture, as well as reduce its acidity.
Most of the bacteria present in Aghogho’s study are common and expected throughout the wine regions of the world. They have also been extensively studied, and their contribution to the winemaking process well-known.
The Tatumella genera, which was overly abundant (61%) within the 2021 vintage but had less than 2% abundance in the 2018 vintage, is much less studied. So how might this organism be affecting the quality of wine between these two seasons? This is a question that we simply don’t know the answer to.
Dr Aghogho Ohwofasa and colleagues’ work highlights that climatic variables, such as temperature, rainfall, and relative humidity, influence the bacterial differences that occurred between the 2018 and 2021 vintage. Rainfall and humidity were key variables driving the populations of bacterial and fungal communities within the 2018 vintage, whilst maximum temperature had a large influence in the 2021 vintage.
Different species and strains of yeasts and bacteria can contribute to the sensory characteristics of wine, which may be beneficial or detrimental to the quality of wine. So, what does this mean for wine making worldwide?
We don’t fully understand the extent to which these ‘wild’ microbes play a role in affecting the flavour profiles and aromas within our wines. Will climate change disturb the composition and abundance of these microscopic winemakers that will ultimately impact the taste of our wines? If so, how do we protect our wine from changing with the times?
This article was prepared by Bachelor of Agricultural Science with Honours student Charlotte Tinsley as part of the ECOL608 Research Methods in Ecology course.
Reference:
Ohwofasa A, Dhami M, Zhang J, Tian B, Winefield C, et al. (2024) Influence of climatic variation on microbial communities during organic Pinot noir wine production. PLOS ONE 19(2): e0296859. https://doi.org/10.1371/journal.pone.0296859
Leave a Reply