By Bryan Calandrelli, Niagara Escarpment Editor

Yeast has to be one of the most underrated, underappreciated and misunderstood elements of wine making. It has so much influence on the final outcome of any wine, that when people ask me how a grape can ultimately show such a wide spectrum of flavors, I respond, “It’s the magic of yeast fermentation.” Well I’m going to try to shed some light on why some yeasts are chosen over others and what factors are considered when inoculating grape juice.

Now I haven’t been formally educated in any way regarding winemaking or viticulture, so I don’t want you to think that I am presenting myself as the Alton Brown of winemaking. The knowledge I’ve collected has been through discussions with real winemakers and two vintages of making wine myself.

At its simplest, yeast is what converts all that natural sugar in the grapes into alcohol. When considering a yeast culture, the main concern is that it will be able to finish this process. On the other hand, when trying to make a wine that keeps some natural sweetness, like a late harvest riesling, one might choose a yeast that dies out at lower alcohol levels.

Another serious concern for winemakers is choosing yeast that will not produce sulfides at excessive levels. This really comes down to how readily available nutrients are in the must (grape juice, pulp, seeds, skins) and the nutrient requirement for a particular strain of yeast. Ultimately nutrients can be added to a must to feed the yeast, but if you’re going for “natural” winemaking, this may be a bit too much intervention to keep that classification.

When you start reading the descriptions of various yeast strains, there are certain attributes that show up over and over. Some indicate good color stabilization or extraction. Many indicate whether they will provide a fast or slow fermentation. Others may specifically claim to give “spicy” aromas or stress varietally correct aromas.

Mouthfeel tends to be another major consideration. Some strains boast of producing a big or full mouthfeel while some say they provide a softer one. 

Others claim to preserve acidity and reduce jammy qualities while some even say that can reduce vegetative flavors in wines like cabernet sauvignon. This is where I think we start flirting with the idea of designer wines. Several of these yeasts, including most of the newer strains, claim to bring out specific flavors in wines, and in my opinion, this doesn’t help to increase diversity in wine.

Ultimately most wines are made from a combination of yeast strains from separate batches. It’s this method that allows winemakers to craft wines that benefit from the best qualities of multiple yeasts. 

There is one type of yeast I forgot to mention, that is wild yeast, the one that naturally occurs in nature in a given vineyard. That’s a whole post on its own, but these cultured yeasts are a good place to start when familiarizing yourself with the unsung hero of winemaking.