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Yeast – Nature’s Wine Maker
As much pride as our world-famous wineries claim to have in their century-old establishments, the majority of the burden of wine making actually falls to a single-celled organism: yeast. In fact, much of the art of wine making is actually the art of feeding and nurturing the yeast. A famous quote from Dr. Roger Boulton from the University of California illustrates: “Ninety percent of wine making has nothing to do with the winemaker. All a winemaker is doing is preventing spoilage, introducing some unique style to the wine and bottling it.”
So what is yeast, and what is it doing? Yeast is a single-celled organism, a strain of fungus. It moves freely in the environment and when it finds nutrition it replicates quickly to form a colony. The earliest known usage of yeast was in ancient Egypt, where it was often used for bread making. In fact, anyone who has ever had to culture yeast for bread making will understand much of what it takes to be a winemaker.
There are many different kinds of yeast, and the ones generally helpful for wine making are of the genus Saccharomyces (Sakchar meaning sugar and Myces meaning fungus), of which there are over a dozen to pick from, each which adds different characteristics to wine. The yeasts of this genus consume the natural sugar found in fruit juice and transform it into almost equal parts of carbon dioxide and alcohol.And there’s the rub: without yeast, it’s just grape juice.
So then, if wine making is an art, then its primary tool is the ability to control yeast. Fresh pressed grape juice will typically already have dozens of different kinds of yeasts, as well as a number of other microbial invaders. If you left the juice as is, it would develop into wine on its own, though it would likely be over-alcoholic and undrinkable. To create a truly great wine, the winemaker must have a specific yeast in mind, introduce it at the right time, feed it and nurture it, and allowing it to die and be cleaned whilst preserving the fruits of its labor. This involves a rigorous control over temperature, humidity, and quality of fruit.
Over the many centuries since wine makers have bottled their products, they have been returning the old skins and seeds of crushed grapes (the pomace) to the vineyards to be used in fertilization. The grape skins are breeding grounds for yeast, and by returning yeast-rich pomace to the vines, vineyards have managed to subtly alter the natural yeasts that occur in their fields. Over time, the selected strain of yeast begins to dominate so rigidly that a winemaker can simply encourage spontaneous fermentation. Those making homemade wines don’t have this luxury, and even established vineyards may be centuries away from such a yeast domination.
So despite the vigilant claims of expert wine makers across the world, it’s obvious that the real master winemaker is yeast.
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Wine Making Yeast Bits
What separates wine from simple juice is the fermentation process in wine making. Fermentation involves wine making yeast, not any other type of yeast like your bread yeast.
Importance
Wine yeast is the most important ingredient in wine making. Not only as an ingredient but the process of mixing it with the must will make or break the whole batch of wine. It is said that the real winemaker is not the person making the wine but the yeast itself. The yeast works to absorb the sugar from the fruit and creating alcohol and carbon dioxide in equal portions.
Timing
The timing of mixing in the yeast is crucial as well. One can neither put the yeast too early nor too late, in the whole wine process. At best, wine making yeast is mixed in at least twenty four hours after the fruit is crushed. And it is left to stand interacting with the must for at least five to seven days, with only a few stirring twice to thrice a day.
Activation
For better results, wine making yeast must be activated first before mixing it into the fruit must. How? Mix the yeast into a cup of juice squeezed from the must and set aside for at least twelve hours before mixing it into the must. Or a cup of warm water will suffice. Do not use hot water as the temperature will kill the yeast rather than activating it. You know the yeast is active when the mixture looks like it is boiling.
Buying
Buying yeast is extremely easy. Just make sure that the label reads wine making yeast or something to that fashion. Any generic brand will make do for the amateurs. But if you are the brave type or already an aficionado, those specialty types are great choices. The amount you buy is also noteworthy, a ten milligram packet of yeast is sufficient to work on ten gallons of grape must.
So you see, even the hardest part of the wine process, which is the part involving wine yeast, is relatively easy once you know why it is crucial, what to buy and how and when to use it.
Yeast in Homemade Wine Making
Yeast kicks off the fermentation process in wine making. After adding it to your must, it begins to consume the sugar, producing equal amounts of ethanol and carbon dioxide.
There are wild yeasts everywhere around us, including on the skins of grapes if you’re making wine from fresh fruits. Generally, winemakers discourage these yeasts from fermenting by adding sulfites to kill them off before they can get started. This is done so the winemaker has more control over the fermentation and can produce a consistent wine from batch to batch.
There are basically two types of wine available to home winemakers; liquid and dry.
Most homemade winemakers prefer to use dry yeast. It’s easier to store and to work with.
A subject of debate among homemade winemakers is whether or not to re-hydrate the dry yeast you’re working with. I’ve found that re-hydrating is really not necessary and in fact can lead to problems if the process is not done exactly right.
Two things that can adversely affect the performance of your yeast are the temperature and also the oxygen level. In order to achieve a proper, vigorous fermentation the temperature needs to be maintained between 70 -75 degrees. There are exceptions and variations to this. Some white wines are fermented at lower temperatures to enhance certain flavors, but special yeast is used to do this.
Oxygen is needed during primary fermentation because the yeast are multiplying rapidly during this stage and without air this multiplying can be severely restricted. During primary fermentation the use of an airlock is discouraged so the wine can get all the oxygen it needs. Primary fermentation lasts approximately 7 days and 70 percent of the fermentation is complete at this point.
During secondary fermentation the wine is usually placed in another vessel with an airlock attached. The airlock is to allow carbon dioxide to escape while preventing bacteria and other micro-organisms. The reduced exposure to air also gets the yeast to stop multiplying and put its energy into making alcohol.
Yeast is a crucial part of homemade wine making. The more you learn about yeast and the fermentation process, the more you’ll be rewarded wine batch after batch of consistent, delicious homemade wine.