Hello, bonjour, and welcome to your new Bonner Private Wines video. You know that wine is fermented grape juice of course, if you watch this channel regularly, you’re probably quite familiar by now with the winemaking process overall. And you know that fermentation is the transformation of sugars in the grape juice into ethanol, a.k.a. alcohol. It is pretty basic and simple, but do you know what fermentation is, really?
Why yeasts ferment grape juice rather than turning it into something else, they turn it into wine? Milk doesn’t ferment like grape juice, does it? You can turn grape juice into yogurt or milk into wine, can you? So let’s have a look at what fermentation is really and how much it matters to the taste of wine. Let’s go.
Why Does Fermentation Happen?
And so, as you know, in the case of wine, what we call fermentation is the transformation by a certain type of microorganisms called yeasts of the sugars, naturally present in the grape juice, namely to be a little bit technical. Glucose and fructose into a type of organic alcohol called ethanol. That’s what you’ve heard. What you probably know more or less already, what you may not have known is that what is called fermentation is the biological or metabolic breakdown of molecules into other molecules using enzymes.
That’s what living organisms do. Now, fermentation generally only occurs when there’s no or too little oxygen in the medium for a far more energy efficient metabolic process called respiration. Using oxygen and respiration, you can break down molecules way better and extract a lot more energy from sugars than using fermentation because you essentially burn off all the sugars to turn them into carbon dioxide and water and a lot of energy.
But if there’s no oxygen available in the medium, you can’t use respiration, you can’t breathe, you can’t break down entirely those sugars. But what you can do is partially break them down and still extract a little bit of energy to survive out of the process. We use respiration, of course, mainly that’s what we breathe. But some microorganisms, despite the absence of oxygen, like in a wine tank, for example, where no oxygen is coming in, they can still live a happy life.
As long as this sugars they use fermentation to get a bit of energy. And because sugars aren’t entirely broken down into CO2 in water, when the wine is fermented, we’re left with a little bit of CO2. Yes, indeed. That’s what makes the bubbles in your sparkling wine or your beer. And we’re left with a lot of alcohol as well.
So yeast are happy with this process because they can multiply and get a bit of energy out of fermentation. And we’re happy because we get alcohol in our favorite beverage. That’s the essence of fermentation.
Yeasts & the Fermentation Process
Yeasts are a specific type of microorganisms that are just by nature really good at fermenting sugar and turning it into alcohol. Fungus are a different type of microorganism, so are bacteria, different DNA, different sizes and those, the fungus and the bacteria, like respiration better generally than fermentation. So we use yeast instead because they don’t totally mess up and eat up our grape juice. That’s kind of their place in nature. Fermenting is what yeasts do really well. So yeasts in winemaking are similar to the ones used for brewing beer or even baking bread.
Similar type. A different type of fermentation is commonly used in the food industry to transform milk into yogurt or cheese, but that’s done by specialized bacteria called the lactic bacteria that convert the sugar in the milk called lactose into lactic acid. As a side note, I won’t get into the details of it here, but we use similar lactic bacteria in wine to convert the malic acid in the grape juice into lactic acid, which is a smoother and softer acid.
And that’s what we call the secondary fermentation in winemaking. But we leave this aside for now. Just know that bacteria do different types of fermentation as well that we can use for making cheese. For example, often in winemaking we use special strains of yeast that have been selected specially to do a great job in the wine yeast strains that like the acidity of wine or that you don’t find in bread or beer, for example, those specialized winemaking yeast, we select them to grow fast and very efficiently, ferment a wine particularly, and we can use those special, specialized, almost engineered strain of yeast into our winemaking process because they work really well.
But winemakers can also just let nature do its thing and let the yeast that are naturally present on the grape skins in the vineyards ferment the wine. That’s what we call natural yeast. They’re all natural. Of course, this new DNA modification for only anything with any yeast at all. But the natural yes, what we call natural yeasts are the ones that are present outside, naturally in the vineyard, naturally yeast or less efficient at fermenting the slower and growing.
And it’s slow fermenting then if you inoculate. But natural yeast work out nicely eventually and they give perhaps more character a little secure to your wine and perhaps more authenticity as well.
Often natural yeast result in lower alcohol content eventually because they have a less efficient fermentation alcohol, sugar into alcohol transformation process that is less efficient, so less alcohol in the wine, which is a good thing nowadays with the global warming and things generally, when fermenting a wine in a tank, you have to have a bit of a cooling system because fermentation releases also a lot of heat and it warms up the wine in the tank a lot to the point that it could actually kill off the yeast that run the fermentation.
So the yeast warm up the tank to a point that it kills them if you let them do that. So we have cooling belts around the tanks to maintain a temperature that we love, the temperature of fermentation also impacts immensely the final quality of your wine. How will taste? A red wine is fermented at a higher temperature than a rosy or white wine, and that’s because the temperature of fermentation affects the byproducts of fermentation.
The Byproducts of Fermentation
I hope I haven’t lost you in too much technicalities here, but if you still hear, I’m guessing you following. So the alcoholic fermentation, that conversion of sugar into alcohol is not a perfect process. Yeasts have to grow and multiply in the liquid in the grape juice during fermentation. Quite a lot to the point that in an active fermenting tank, an inch square of liquid contains hundreds of billions of individual yeast cells.
So yeast not only create alcohol, but they also create loads of other molecules in the process that we will find in our final wine what we call those byproducts of the fermentation. The main one is a substance called glycerol, which is a type of liquid, a sweet and oily, slightly fatty molecule if you wish. It’s how you can describe it.
And the fact that fermentation also produces glycerol is a great thing because it impacts the oily texture of a wine. It makes it smoother and softer and more textural to the palate. That’s also why a totally dry wine that would virtually have zero sugars left would still taste a little sweet because glycerol tastes sweet and there’s quite a bit of glycerol into wine.
Alcohol itself tastes a little sweet as well. Now you also produce hundreds of different molecules that affect the aromas of a wine as well. A lot of them are various esters that smell like fruit, like banana, like strawberries, like pear, which are a large part of why wine smells like different fruits other than grapes. Yeast make some smoky molecules.
They make some buttery molecules, they make some yeast molecules. Of course they make some fruit smelling molecules as well. So fermentation is a huge part of why wine is so complex and refined eventually has such a great complexity. It’s not just the aromas of grape juice. Those aromas of grape juice are combined, augmented by the aromas of the fermentation itself, which overall gives each wine a really unique, aromatic and flavor profile, because there’s so much complexity in the process.
Fermentation really reveals and fulfills the potential of a wine. It’s the crucial and fundamental part of making wine somewhat like how you cook a piece of meat will make a world of difference in how your steak or your roast will taste eventually. And like cooking, fermenting is a complex process to master and control, especially because it’s a natural process that you cannot absolutely 100% control perfectly.
And this is the art, my friend, of winemaking, because we’re working with nature here to make it as close to perfection as we aspire to as possible. A big part of the artistic aspect of wine is knowing that perfection cannot be achieved in a wine, and it doesn’t have to. How you appreciate yourself, the uniqueness of each and every wine and how you can perceive how close to a subjective perfection it is, is what makes the difference between a wine that you enjoy immensely and a wine with no life, no magic to it. That’s the whole difference.
On these final metaphysical thoughts. I’ll leave it here for today and I will see you soon. In the wonderful world of vino. Cheers!
