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Fermentation and The Development of Flavours

By: Mackenzie Brisbois
On the most basic level, fermentation is the conversion of sugar into alcohol and carbon dioxide by yeast. But what affect do yeast have on the flavours in a wine? Yeast produce Carbon Dioxide and Alcohol, give off heat and are also responsible for the development of flavours.
About 400 of 1000 flavour compounds are yeast derived!!!
Primary, Secondary and Tertiary Wine Flavours
To further understand where flavours come from in wine, we need to understand that they are categorized into 3 tiers in wines: primary, secondary and tertiary.
• Primary flavours in wine are grape derived flavours – like bright green pepper in a Cabernet Franc. Although yeast play a crucial role in converting grape juice to alcohol, they also affect the development of the primary flavours. How that green pepper is perceived will be different with different fermentation dynamics. For example, are the yeast hot or cold?
• Secondary flavours are those developed during fermentation. These tend to fall into the yeasty, creamy, buttery category. Secondary aromas in wine can develop from fermentation, malolactic fermentation, and extended aging on the lees (the dead yeast).
• As wine ages, primary fruit flavours recede and more complex tertiary flavours such as nuttiness, earth, mushrooms, floral and spice may develop.
Yeast – One Essential Job with Multiple Outcomes
There are different yeast species that function in the winemaking process – all having slightly different ways of getting to the end goal – wine! Some being more tolerant to alcohol than others. Each type of yeast has a different way to go about the process of getting to alcohol and along this journey, the flavours of wine are created.
A Few Types of Yeast
The main wine yeast is Saccharomyces Cerevisiae – this yeast is alcohol tolerate, likes warm ferments, plenty of oxygen but doesn’t like it when the alcohol gets too high. Rarely found on grapes coming in from the field, this yeast hangs around cellars.
Wild yeast – like Kloeckera and Candida – these are the yeast present on grape skins at harvest. Without an addition of sulphur dioxide these yeasts usually start fermenting, but generally die off around 5%, at which point S. Cerevisiae takes over. The wild yeast tends to produce higher volatile aromatics and are generally thought to be a little crazier to control.
Inoculated Versus Spontaneous
A lot of wine is produced with added yeast. Specific strains are selected to bring out specific end results in wine – like increased fruitiness or smooth mouthfeel. Some yeast strains have different fermentation dynamics like low foaming or better function at low temperatures. When it comes to choosing yeast to make wine there are a lot of colours to choose from and you can dial in the stye of wine you want to make quite specifically.
To clarify, this is completely opposite to how I make wine.
I bring in my grapes and see what the yeast can do year to year. It’s quite a wild game of reacting to fermentation – coaxing the wine to tastiness without knowing what pathways the yeast will be taking.
In life I’ve always been a bit of an overachiever and an excessive worrier. Prior to harvest I really plan out what I want to do with the grapes and wines each year. What I find, is that as much planning and predicting as I do, the yeast always take things in a different direction. So essentially, my job, is not to predict what I’m going to make, but to react to what is going on and shape it into something tasty.
The planning does still help though!
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