Little Fermented Worlds: The Science of the Life in Wine
Freshly pressed 2023 Syrah. This wine is still full of yeast that are doing many important jobs for us.
Introduction
If you've ever been curious about the fundamental process behind making wine, cider, beer, ambrosia, or any other alcoholic beverage - fermentation - this article has got you covered. We'll explore the significance of yeast and yeast biodiversity in alcoholic fermentation. Let's delve into the world of fermentation and discover its secrets!
The Essence of Fermentation: The Fundamental Process Sustaining Life on Earth
Fermentation is perhaps the most crucial and fundamental biological process to all life in on earth. Without its development, life may not exist today. It was used by the most primitive organisms that ever existed, billions of years ago, to get energy from food and create conditions in which other life could flourish. Far from being mystical or mysterious, it’s something that takes place all around us - and within us - constantly.
Though there are several different types of fermentation, the most basic principle remains the same.
Fermentation is a process utilised by cells to extract energy from food molecules in the absence of oxygen.
Complex organisms like you and I typically use respiration (which requires oxygen) to get energy from food because it’s around 18 times more efficient, but some of our cells can resort to fermentation when oxygen is running short, such as while playing sport. The burning sensation you feel while doing intense exercise is the result of your muscle cells swapping from respiration to a type of fermentation called anaerobic glycolysis, to ensure that your muscles have enough energy to carry out whatever task you’re doing.
Yeast Are the Key to Alcoholic Fermentation
Yeast are single-celled microorganisms belonging to the fungus kingdom. They play a crucial role in converting sugars into alcohol and carbon dioxide through anaerobic fermentation, as you can see in the diagram below.
The yeast are using fermentation to get energy - the ethanol and CO2 they produce are by-products of this process. For every ~17g of glucose they consume, they produce 1% ethanol in 1L of solution, meaning that if we know how much sugar there is in a solution e.g. wine must or a honey & water solution to make ambrosia, we can estimate how much alcohol we’ll end up with at the end.
Exploring the Impact of Yeast Biodiversity on Wine’s Sensory Characteristics
Saccharomyces cerevisiae is the yeast we hear about the most in wine, but there are many, many more species involved in a natural wine ferment. Image Credit: Kateryna Kon/Shutterstock
Researchers have identified at least 1500 species of yeast around the world, though this is likely only a small representation of the incredible diversity of yeast out there. We most commonly hear about Saccharomyces cerevisiae, but in a single wine alone, 61 different yeast species have been found to be present. There’s no doubt that S. cerevisiae plays an important role in fermenting wine, but it certainly doesn’t act alone.
And, though we often hear about the “risks” of working with natural and biodiverse yeasts, there are actually a number of known benefits to yeast biodiversity in wine, which we can assume translate to other beverages. For example, yeast biodiversity significantly influences the sensory characteristics of wine. Different yeast species and strains produce diverse aroma and flavour compounds during fermentation, such as esters, aldehydes, and terpenes, contributing to the wine's aromatic profile. Additionally, yeast diversity affects flavour complexity through the production of compounds like fatty acids, alcohols, and volatile phenols. These compounds add nuances and depth to the wine's taste perception.
Moreover, yeast can influence mouthfeel and texture by producing glycerol and polysaccharides, impacting the wine's overall body and mouthfeel. The fermentation kinetics and tolerances of yeast strains can also affect the duration and outcomes of fermentation. Furthermore, the use of indigenous yeasts found naturally in vineyards can contribute to terroir expression, providing sensory attributes specific to the region.
The Power of Yeast Biodiversity: Enhancing Resilience and Stability in Alcoholic Ferments
But yeast biodiversity in our beverages may yield a benefit that goes beyond sensory qualities. Biodiversity is one of the hallmarks of healthy ecological systems. It’s kind of like having a toolkit with just a hammer and a saw, compared to one that has a hammer, saw, screws & bolts, nails, spanners and shifters, and screwdrivers. You don’t need all of these all the time and some of them do similar jobs. But I bet you’d rather have a toolkit with more in it, rather than less, when something goes wrong, because then you have more options and you can respond more quickly and precisely. In ecosystems, the presence of multiple species that can do similar things is referred to as redundancy, and it’s used as a measure of ecosystem health. It creates flexibility, as well as a backup system, which enhances adaptability. Ecosystems that are more diverse are quicker to respond to change, and tend to recover more quickly from shocks and stressors, making them more resilient.
This next bit is a little tricky, but stay with me, because this is an important concept to understand. Systems that have this kind of capacity to respond to change and reorganise themselves are known as “dissipative structures”, of which there are several types but they all follow the same principle. Even as they become more complex, they become more organised and finely tuned. The circadian rhythm is an example of a dissipative structure that you’re probably already familiar with. It’s a self-organizing system that regulates biological processes, including sleep-wake cycles, in a cyclic manner. It maintains stability and adapts to environmental changes, providing an essential internal timing mechanism for organisms. This complex process emerges from the interaction between genes and proteins within cells, creating a finely tuned and organized system. If you’ve ever suffered from insomnia for a period of time, then you know exactly how devastating changes to this dissipative structure can be. We need sleep to think and feel our best, though if we did nothing but sleep, we would miss out on a whole heap of other things in life that we need, like exercise, socialising, and eating.
This is an example of a spatial dissipative structure, where tiny amoebae have organised themselves into concentric patterns (Goldbeter, 2018). Can you imagine this as a diagram representing your circadian rhythm as you’ve grown and developed? You continually pass the same point, which could represent time or space, but as the complexity grows, so too does the need for coordination and organisation of activities to maintain the pattern.
In the context of microbiological life forms, they too are organised in such a way that their actions are cyclic. In a sense, they change in order to try and keep things the same. That is, life makes changes to itself and the world around it as an act of self-preservation, in an attempt to retain conditions in which it (or its progeny) has the ability to flourish. The more organisms there are doing this, the more stable the conditions. This is one of the reasons why our current rate of biodiversity loss is so concerning - it’s expected to disrupt the way in which finely tuned earth systems are regulated, and will likely result in suboptimal changes in earth’s atmosphere and climate, independent of climate change.
In alcoholic ferments, yeast produce volatile compounds, antimicrobial agents, and antioxidants, all of which protect wine from oxygen, regulate pH and stability, contribute to the breakdown of potentially “off” flavours such as those associated with mouse taint and brett via the action of mannoproteins (more to come on these little wonders in a later post!), and contribute to the creation of long-chain flavour molecules that are more stable and less prone to being oxidised than their smaller counterparts. We’ll explore some of these activities in more detail in later posts, but since every yeast is slightly different, there’s good reason to believe that a more biodiverse yeast population will do all of these things more effectively and efficiently than a less biodiverse one and negate the need for additions.
Conclusion
In the realm of fermentation, yeast is a vital player, transforming sugars into alcohol and carbon dioxide to craft various alcoholic beverages. With over 1500 yeast species, their biodiversity significantly impacts the sensory experience of drinks like wine, cider, beer, and ambrosia. Varied yeast strains contribute to diverse aromas, flavours, mouthfeel, and texture, enriching the final product. This diversity enhances resilience, creating a versatile toolkit to adapt to changes and stressors, ensuring a stable and efficient process. Embracing yeast biodiversity protects drinks from oxidation, maintains pH and stability, and breaks down undesired flavours, reducing the need for additives.
By understanding ferments as tiny ecosystems, we can begin to increase our awareness of the natural processes inherent to them and how they interact. Not only can this be an important part of appreciating the wine we drink; it’s also an important part of understanding how we can nurture them through the entire process from vineyard to bottle, a topic that we’ll explore in another post.
References
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