Magical Mannoproteins: Winemaker's Secret Sauce
Introduction
When it comes to making wine without the use of additions or fancy machinery, one of our tasks is to figure out how we can make something that’s expressive, stable, and delicious based on the resources available to us - basically, grape juice and yeast. This might sound challenging but actually, it’s perfectly possible, though it does take having a more comprehensive understanding of the principles governing biochemical reactions taking place in the wine as it ferments and ages. We’ll be going over these in more detail in coming posts but I wanted to introduce you to mannoproteins as a starting point.
What the heck are mannoproteins?! I hear you ask. I’ve come to think of them as winemaker’s secret sauce; they perform so many different roles in wine that I think it would be difficult for anyone to say their wine hasn’t been influenced by them, at least to some degree. They make everything in winemaking that much easier and contribute to our enjoyment of the final wine in more ways than we could count. Below, I’ll describe what they are in a little more detail.
What Are Mannoproteins
Yeast lees at the bottom of an ambrosia ferment. No doubt the mannoproteins being released as it ages are working their magic.
Mannoproteins are a group of complex carbohydrates (mannose-based) and proteins found in the cell walls of yeast. Some winemakers buy commercially available mannoproteins to add to wine, but they are released into wine (and other yeast-based ferments) during yeast autolysis, a natural process that occurs when yeast cells die and break down during fermentation or aging. This means that by keeping the wine in contact with its lees for a period of time, the activities of mannoproteins can be utilised to affect wine’s inherent attributes.
Mannoproteins are known to influence various aspects of wine quality, including mouthfeel, aroma, and stability. There are numerous types of mannoproteins, with different types of mannoprotein derived from different yeast strains. The different mannoproteins also make different contributions to wine’s sensory attributes and stability, meaning that a more biodiverse yeast population will result in more types of mannoproteins, so more tools in the toolkit of the winemaker.
The exact number of distinct mannoproteins can be challenging to determine as research in this area continues to evolve, and new variations are discovered. They are primarily classified into two main types: high molecular weight (HMW) mannoproteins and low molecular weight (LMW) mannoproteins:
High Molecular Weight (HMW) Mannoproteins: These are larger mannoproteins found in the cell walls of yeast, which are primarily involved in enhancing wine mouthfeel, body, and stability.
Low Molecular Weight (LMW) Mannoproteins: These smaller mannoproteins, released from yeast cells during autolysis, contribute to wine aroma and flavour by binding to and releasing volatile aroma compounds.
Next, we’ll take a look at the current understanding of mannoproteins contribution to wine’s sensory characteristics, as well as their role in stabilising wines.
Yeast autolysis. Note that some of the cells have holes beginning to appear in them, some are almost fully degraded, and others are still intact. From Martı́nez-Rodrı́guez, Polo & Carrascosa, 2001.
Mannoproteins Contributions to Wine’s Sensory Qualities
Viscosity & Body
HMW mannoproteins contribute to the viscosity of wine. This increased thickness or fullness on the palate is often associated with a richer body and more substantial mouthfeel. For example, HMW mannoproteins can interact with glycerol, a type of alcohol typically produced in ferments with a higher starting sugar concentration to regulate osmotic pressure. Glycerol is known for its sweet, smooth, and slightly oily texture. It’s more viscous than ethanol, which is due to stronger bonds between components that allow it to form larger molecular structures. HMW mannoproteins can form complexes with glycerol which contributes to wine's mouthfeel and the perception of more body. The interaction between mannoproteins and glycerol can enhance this effect.
Astringency Reduction
HMW mannoproteins have been shown to reduce astringency in wine. Astringency, characterized by a drying or puckering sensation, is due to the presence of polyphenols in the wine, perhaps most notably tannins. Mannoproteins can bind with tannins, resulting in larger, less reactive molecules. This reduces the perception of astringency because the tannins are less available to interact with salivary proteins in the mouth, thus diminishing their ability to cause astringency. HMW mannoproteins also contribute to the overall polysaccharide content in wine. Polysaccharides can enhance the wine's mouthfeel and mask astringency by creating a smoother and more rounded texture, providing balance and creating tension between astringency and a more luxurious palate. If you’ve ever tried a high-tannin wine, such as Nebbiolo, before it’s been subject to extended micro-oxygenation (oxygen in small, steady quantities acts as a catalyst for biochemical reactions in wine), you’ll understand just how significantly mannoproteins can influence the final wine.
Capture and Release of Aroma Compounds
LMW mannoproteins have the ability to bind to and release volatile aroma compounds that are naturally present in wine. Because they have hydrophobic (water repelling) regions, they interact with hydrophobic aroma compounds. These interactions effectively "capture" the aroma compounds. Under certain conditions, such as changes in temperature or pH, LMW mannoproteins can release the captured aroma compounds. By facilitating the release of these volatile compounds, LMW mannoproteins make them more available for sensory perception. This interaction can significantly enhance the aromatic profile of the wine. For instance, they play a significant role in the production of fruity and floral notes in wine through their interactions with esters, terpenes, and other aromatic compounds.
Reduced Perception of Undesirable Aromas
LMW mannoproteins can interact with and sequester compounds responsible for undesirable wine aromas, such as sulfur-containing compounds. This interaction effectively minimizes the perception of off-flavors and contributes to the wine's overall flavour quality. As an example, you’ve probably heard of Brettanomyces, a strain of yeast that produces barnyard-like aomas and is considered (by some, at least) to be a fault in wine. By binding to volatile phenols and other compounds produced by Brettanomyces, LMW mannoproteins can reduce the sensory perception of it over time, so long as there isn’t too much sulphur dioxide or other preservatives to arrest their activity. Likewise, mannoproteins can ameliorate “mousiness”, which smells just like it sounds and is attributed to the presence of Brettanomyces in conjunction with specific strains of lactic acid bacteria, through binding to compounds that contribute to its perception, such as 2-acetyl-tetrahydropyridine (2-AP).
Influence on Sweetness and Perception
LMW mannoproteins have the potential to influence the perception of sweetness in wine. By binding to sweet taste receptors T1R2 and T1R3, they make our taste buds more sensitive to sugars in wine, enhancing our perception of sweetness. Additionally, because they bind to polyphenols as previously mentioned, they can reduce our detection of astringency, which results in an enhanced perception of sweetness.
Stabilization
Unfiltered and unfined, yet still clear. Mannoproteins act as natural clarifying agents in ferments.
Mannoproteins contribute to wine stability in several ways. For instance, they act as antioxidants in wine, scavenging oxygen and free radicals and preventing unwanted oxidation. They also inhibit the growth of certain wine spoilage microorganisms. By binding to specific yeast mannoprotein receptors on the cell surface of spoilage microorganisms (example), mannoproteins can interfere with their growth and proliferation. Another important role that they play in stability is through polymerisation, the process of smaller chemical compounds aggregating into larger ones, which tend to be more stable in the presence of oxygen. HMW mannoproteins contribute to the colloidal stability of wine by preventing the precipitation of polymeric phenolic compounds and tartrate crystals, which create “haze” or sediment throughout the wine, resulting in wines with brighter colour and natural clarity. HMW mannoproteins can also aid in tartrate stability. They help inhibit the precipitation of potassium bitartrate crystals (cream of tartar) in bottled wine, which can release bitter compounds in the wine or be a little bitter to taste if you get some in your glass. All of these different activities for those of who work without additions or external stabilising agents; I’ve learnt through trial and error that wines will often correct themselves over time if left to their own devices without the addition of sulphur, so long as they are carefully handled throughout the winemaking and ageing process. Mannoproteins are most certainly one of the key mechanisms for their ability to create their own inherent stability.
Complexity
I think it goes without saying that mannoproteins contribute to complexity in wine. Because they interact with so many different sensory aspects within wine, they allow each to be expressed in a balanced and nuanced way, helping to create a layering effect to our sensory perception of wine. Collectively, an array of mannoproteins will prevent any one flavour, texture, or aroma from becoming predominant, whilst allowing all of the different facets to work in harmony with one another. As such, they are indisputably one of the unsung heroes of quality wine.
conclusion
In conclusion, mannoproteins, found in yeast cell walls and released during autolysis, play multiple roles in shaping the final wine's character.
High Molecular Weight (HMW) mannoproteins contribute to viscosity and body, reducing astringency, and enhancing wine stability. They interact with glycerol, providing a fuller mouthfeel and can bind with tannins, reducing the perception of astringency. Moreover, HMW mannoproteins prevent haze formation and tartrate precipitation, ensuring a more stable wine. Low Molecular Weight (LMW) mannoproteins influence wine flavour by binding and releasing volatile aroma compounds, enhancing fruity and floral notes. They reduce the perception of undesirable aromas and can even influence the perception of sweetness in wine. Additionally, mannoproteins contribute to wine stability by acting as antioxidants and inhibiting spoilage microorganisms.
Their diverse roles in wine production, from enhancing sensory qualities to stabilizing the final product, make mannoproteins invaluable to winemakers seeking to create expressive and high-quality wines. As research in this area continues to evolve, a deeper understanding of mannoproteins will further refine winemaking practices, making them an essential tool in the winemaker's arsenal.
Mannoproteins are indeed the "secret sauce" that silently elevates the art and science of winemaking, resulting in wines that delight the senses and stand the test of time.
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