The Wine Blokes

If you don’t know how grape juice is turned into wine, you’re probably in the wrong place. On the off chance you made it to this site accidently, grape juice is converted into wine by a little critter called yeast. Yeast of course is used in many food and beverage processes, including cheese, breadmaking & brewing. In simple terms, yeast convert the sugar in the grape juice into alcohol. So what’s so special about the process? Nothing really, it naturally occurs everyday, everywhere. However, in making wine, it’s how you use yeast that is the trick.

In ancient times, natural yeast in the atmoshpere would have initiated fermentation. Today there are two main ways of innocualting wine juice with yeast to initiate fermentation. However a much more intensive third method is used by very few wineries aorund the world, but can have dramatic beneficial effects on quality.

The most common method these days of innoculating grape juice or must, is by rehydrating freeze dryed “packet” yeast that you purchase from your local winery supplier. Essentially it looks and smells similar to the yeast you would buy in a packet at the supermarket to bake bread, with the exception that the overwhelming majority of yeast used in winemaking is a strain called “Saccharomyces cerevisiae”. The benefit of this method is that winemakers can be relatively confident that the packet yeast has undergone strict quality control, is uniform, and extremely easy to use.

The other widely used method is still the natural or “wild ferment”. The grape juice or must is allowed to undergo fermentation by the natural yeast population in the winery. Generally, a dominant form of yeast will be present in the atmoshpere, and through experience, many winemakers will decide to allow natural fermentation under these conditions. Wines made this way can have exotic and complex characters that may be beneficial, however the danger is that the winemaker is never entirely sure what strain of yeast is dominant. The dominant yeast population may develop undesirbale flavours and characters in the wine and hence the risk is much higher than packet yeast. It doesn’t get much easier to implement though. You just crush the grapes, and let it go.

The third, and less common method, and much more intense, is growing a known population from agar slopes isolated in the laboratory. It is a much more scientific and labour intensive approach but can have great benefits if done properly. Very few wineries use this method in it’s entirety.  Essentially,  a desirable strain of yeast is isolated from the winery. It may have been found in a tank, a wine barrel, a grape bin, or even in the vineyard.  Generally the yeast are isolated as the dominant yeast in a wild fermentation that created complex flavours or a very desirable character.  Under sterile conditions, the yeast are allowed to grow on agar slopes (below), until thay are needed.

When needed for fermentation, the yeast are transferred from the agar slopes under sterile conditions to a small vessel such as a 20 Litre stainless steel cannister, where they are allowed to reproduce and populate in a sterile grape juice environment. As the population develops and becomes stronger, the yeast culture is progressively grown up in larger vessels until it is suffucient and strong enough to be introduced into raw grape juice for ferment. The entire process may take between 5 and 20 days, depending on the conditions.

However the benefits of this process are that the winemaker can be confident in the purity of the culture, and also may be able to produce wine with a distinct point of difference due to the indigenous yeast population. It does however take highly developed scientific and laboratory skills to implement correctly.

Great examples of wines made using this method in Australia are many Petaluma wines, and some of the Mountadam range from the Eden Valley. Both wineries have developed a reputation for distinctive, high quality wines, not least due to the fact that they culture their own yeast.