Yeast, Yeast, and More Yeast!
Posted by genllerena on October 29, 2007
Yeasts are really the unsung heros of our civilization. Without yeast there would be no wine – perish the thought – only grape juice. There would be no cider, no beer, no vinegar (it’s a derivative of the three aforementioned beverages), no bread, no pizza, and the list goes on. I think you could make a case that there indeed would be no professional sports. Sure high school and college sports would not be gravely affected, but if I’m going to pay to see grown men (who make more money in a year than most people will ever see in a life-time) kick, hit or pass a ball around, I want – no need – a beer. Pizza is a close second. Really life as we know it would be radically different without the humble yeast.
So, what do yeasts really do? Here’s the simplified version: Yeasts breakdown (will call it eat) sugar and nutrients and produce alcohol, carbon dioxide, volatile metabolites, heat and more yeasts. They are the vital ingredient for turning grape juice into wine. It’s easy to point to alcohol production as the key byproduct of yeast activity, which is exactly what the government does. But you would be missing one of the yeast’s most amazing accomplishments – volatile metabolites. These are the esters, sulfur compounds and volatile fatty acids that make wine more flavorful than the grape juice it is derived from. No one sits around with friends expounding on the wonderful mouth-feel and aroma of grape juice; but there are thousands of websites devoted to those aspects of wine. Many of the compounds that give wine its flavor, aroma, color and mouth-feel are released or modified by the yeast during fermentation.
Wine makers choose yeast based a variety of attributes. The first thing a winemaker does is determine which yeasts are suitable for the wines that she is making. Yeast strains have been isolated to compliment different grape varietals, because of the different volatile metabolites that they create, and their ability to ferment in varying levels of alcohol and temperatures. Next a winemaker needs to determine what qualities should be enhanced or reduced in the wine. For example, a winemaker making Cabernet Sauvignon may choose BDX (Bordeaux Red) if she is worried about color loss or to enhance aromas. If the Cab had to be picked a little earlier than optimal, or if it has nice spicy aromas, she might pick CSM instead. Personally, I like to break up the fruit into two or more lots and use different yeasts in each tank. This way I can develop more complexity in the finished wine when the tanks are blended together. I get most of my yeast from Vinquiry as they have a nice selection. Here’s the link if you want to know more about available yeasts http://www.vinquiry.com/pdf/YeastDescription0607.pdf .
I would be remiss if I didn’t also mention the natural, or native yeast, fermentation method. Many wineries are using this method for fermentation, and while it may seem Nouveau, it has been used for several millennia. For a natural fermentation the wine is not inoculated with a commercial yeast, hence the name natural. The winemaker allows the yeasts that are present on the fruit to carry out the fermentation. On the surface this sounds like a very straightforward and simple way to make wine. It’s very inexpensive and after all isn’t this the way wine has been made for thousands of years? Well yes, BUT… When wine is inoculated with a commercial yeast, that yeast dominates the fermentation from the very beginning to the very end. They have been isolated because they are hardy in very inhospitable environments, when the must is at low temperatures and high in sugar and when the must is at high temperatures and high in alcohol, and also because they produce flavors and aromas that are pleasing. During a natural fermentation yeasts of several different genera are active with different types of yeasts dominating during different stages of the fermentation process. The hope is that in this mix of yeasts there are those that hardy both at the start, in high sugar, and at the end, in high alcohol, and that they produce a wine that is pleasing. But, there is no guarantee that this will be the case. And, there are few things more terrifying than a fermentation that stops before the wine is dry. This is where the winemaker earns her keep.
So there you have it, a very brief introduction to yeast. Please remember them when next you have a glass of wine, or a slice of pizza.