As far back as history can tell us, man has been making wine. Archeologists have found evidence of wine being purposely made as far back as 12,000 years ago. Wine was very present in early Egypt, almost being an industry of its own as early as 2,000 B.C. Yet, wine yeast was not discovered until the 1850's when French scientist Louis Pasteur suggested that wine fermentation was the result of a living organism.
So why do we need to use wine yeast now, when for so many years man has successfully made wine while being completely oblivious to its existence? There are two parts to this answer...
Part I, Putting The Odds In Your Favor
To say that man has successfully made wine over the years is not completely true. Bad batches of wine where made quite often as well. Wines that developed mold; wines that remained cloudy and visually unappealing; wines that eventually turned to vinegar - they were all part of the mix of what was made along side the good batches of wine that kept man's interest in the drink for so long.
Yeast is naturally everywhere. We can't see it, but it's in our homes, on the trees and plants; it floats in the air. We breath it every day. And it is this natural yeast that also lands on fruit and provides for a natural fermentation when we crush the fruit and expose its sugars and nutrients to the yeast.
The problem is that natural yeast is a "package deal". What I mean to say is that yeast is not the only thing that is everywhere. Vinegar bacteria, mold spores and many other types of little "nasties" are on the fruit as well, waiting to spoil the fun - pun intended.
Yeast does have the upper-hand in the sense that it is, on average, more capable of taking over the fruit more so than these other competing organisms. It is also capable of actually destroying any remnant numbers of these other organisms once it has taken hold of the fruit. But, quite often yeast will let us down and allow these other cultures to take over the fruit and cause it to become something other than wine.
And, this is how the unknowing story went for so many years. In the more current times, since Louis Pasteur's discoveries, we have developed a better understanding of what takes place during a fermentation. We understand that natural yeast is a "package deal". We now know how to isolate a strain of yeast, preserve it and package it.
With pure strains of packaged wine yeast available, the winemaker can now simply put the juice through a sterilization process, killing all the wild molds and bacteria (wild yeast included) and then simply add a fresh strain of packaged yeast back to it, allowing the winemaker to start with a clean slate and a big advantage.
The sterilization process is very simple. You add a product called Campden Tablets to the juice - one tablet per gallon. Let the juice stand uncovered for 24 hours and then the juice is ready for wine yeast to be added.
Campden Tablets are really sulfite that is stabilized in a powder form. When the tablets are crushed up and dissolved into a fruit juice, they release sulfur gases into the wine which does the sterilizing. Over a short period of time the gases slowly dissipate into the air, usually within 24 hours, making it safe to add your fresh package of wine yeast.
Part II, Taking Advantage Of Technology
The second reason we should add yeast to wine, is that the strains that are available to us as winemakers are much more suited for making wine than what you will find floating in the wild. Like any other living organism, yeast can be bred to respond more favorably to a given situation. There are yeast that have been bred specifically to make beer; yeast bred specifically to rise bread and so on.
In the case of wine yeast, these yeast are not only bred to heartily produce the maximum amount of alcohol they can from the fruit, but also to produce alcohol with good flavor qualities. And to take this a step further, different wine yeasts have been bred for different types of wines. For example, there are wine yeast, such as our "Pasteur Rouge" yeast from Red Star, that are very well suited for heavier red wines. And, there are wine yeast such as our Lalvin ICV D-47, that are very well suited for light, fruity white wines, and so on.
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Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.