Posted by bruce-bradley on January 30, 2014 at 12:50 AM

People often ask me about yeast and wine and I’m sometimes surprised by how little most people seem to know about yeasts, so I thought I’d write a few words about it.  Of course, knowing me, it’ll be more than a few words, but we’ll start out that way…


First off, without yeast there would be no fermentation and, without fermentation, there would be no wine. Yeasts are microbiological (very small) creatures that consume the sugar in grape juice and convert it into alcohol. We like yeasts. 

There are dozens (probably hundreds, but I haven’t counted all of them) of packaged yeasts out there, their manufacturers all telling you that this yeast is the right one for your wine.  Some are old standards that have been favorites with winemakers for decades, like Red Star or Pris de Mousse, but new ones are being developed each year. Some yeast manufacturers say that their yeast will give the wine a big, bold flavor.  Others will give you a wine that is more delicate and elegant.  There are whole catalogs of wine yeasts—this one for Cabernet, that one for Syrah, and so on.  With the popularity of higher alcohol wines came a need for even more specialized yeasts, for when the alcohol reaches a certain level it will kill off many strains of yeasts, and the last thing any winemaker wants to deal with during harvest is a stuck fermentation (well, actually, there are a number of  “last things” that winemakers want to have to deal with, but this one’s pretty high on my list).


One thing that many people that I speak with seemed to be confused about is the fact that wines don’t really need to be inoculated with yeast at all, because there is already yeast on the grapes when they are brought in.  During Prohibition the late, great Antonio Perelli-Minetti went from making wine to producing a grape juice concentrate.  He sold the concentrate in gallon cans and placed a warning on the side of the can that read, “Do not dilute this concentrate with water and leave it in a warm place, or it will turn into wine, which is illegal.”  Of course, he sold a lot of concentrate. One day a government man showed up at his production facility and said it would have to be shut down, because the facility was infected with yeast.  Perelli-Minetti said to the man, “Really…show me this yeast.”  So, the government man produced a microscope and, sure enough, there was yeast.  Perelli-Minetti then took the man out into the vineyard, where they again found yeast. Then he took the man to a spot miles from any kind of fruit production whatsoever.  Once more, they found yeast.  Perelli-Minetti told the government man, “You people find a place where there is no yeast, and I’ll go there and build a new plant.”—and kept producing his concentrate.


Do yeasts affect the flavor of wine?  Absolutely!  For most of my winemaking career I was taught that the main reason we inoculated with domestic strains of yeast was because wild yeast can give an off-flavor to the wine.  This may be true in some cases, but the opposite is also true.  In 2006 I was making wine for Wm. Harrison winery and we decided to make Pinot Noir.  Since most of the winery’s grapes are estate-grown Bordeaux varietals, we had to buy the grapes, which we got from a vineyard on the Sonoma Coast.  We ended up with three fermenting bins (enough for 150 cases) and I decided to experiment.  Using dry ice, we did a 5-day cold soak (this was cool—the dry ice creates fog, which covers the fermenting must and made punching down seem like something out of a vampire movie), and then I inoculated one bin with yeast and let the other two bins ferment from wild yeast.  The inoculated bin was my security blanket.  I fully expected the bins fermented with wild yeast to have some off and undesirable flavors.


I was wrong.  The two bins that were fermented from wild yeast were amazing and far, far better than the bin I had inoculated.


Live and learn.


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Reply kelly
7:44 PM on January 30, 2014 
I always enjoy reading your blogs Uncle Bruce!
Reply Dianna
8:32 PM on January 29, 2014 
Hey Brother, another well written , enlightening article. Although I worked in the wine industry for many years, the wine making was not my area of expertise. Thanks for the insight. I'm looking forward to future articles!