I mentioned several factors to consider when selecting yeast for fermentation in the previous article. Let's look at some of them in more detail.
Grape variety and wine style are often the most important factor to consider.
- One may want to avoid a vigorous, high-alcohol tolerant yeast like Lalvin EC-1118 (prise de mousse) when residual sugar (RS) is desired after fermentation. Why? The ferment will be far easier to control and stop with a weaker yeast such as EnoFerm M1.
- If fermenting lower quality red varieties, one may want to choose a yeast such as RC-212 that will provide enhanced color extraction and stability.
Fruit quality and price-point are two other major considerations. Poorer fruit quality requires more attention due to several factors, including decreased nutrients and presence of undesirable microorganisms. In contrast, grapes and juice destined for low price-point wines typically receive far less attention and monetary input.
- A winemaker doesn't want to use expensive specialty yeast like Zymaflore Alpha to ferment fruit destined for the bulk market or cask wine. Why? It's not cost-effective.
- Poor quality fruit destined for a higher price-point product shouldn't be fermented with indigenous yeast and should probably be inoculated at a higher rate. Why? The winemaker should try to reduce the risk of a poor fermentation.
Different yeasts require different conditions during fermentation to perform with optimal kinetics. Selecting the right yeast requires determining and considering all conditions it will need to perform under.
- Brix (sugar level) - When higher brix grapes are required to ferment to dryness (less than 2 g/L residual sugar), then a yeast with a higher alcohol tolerance is suggested.
- Ferment temperature - Most yeast strains have specific temperature ranges in which they will work best. If a winemaker is aiming to ferment a wine at low temperature, maybe with the aim of maintaining volatile compounds of an aromatic white variety, choosing the right yeast can make a big difference.
- Tank vs. barrel fermentation - When fermenting wine in barrel, a low-foaming yeast will help avoid spillovers.
- Compound production - yeast with a high flocculation rate and high glycerol and polysaccharide production is often desired as well to bolster body in these wines and with reds like Cabernet Sauvignon.
- Nutrient availability - Some yeasts have higher nitrogen requirements than others. Choosing one of these strains in a low nutrient situation can lead to an easily avoidable unsuccessful ferment.
- Malolactic fermentation - If a wine is destined to undergo malolactic fermentation, a yeast may be chosen that will not produce high levels of sulfur dioxide, and maybe chose one that either increases or decrease titratable acidity.
Yeast manufacturers typically provide extensive recommendations for each of their yeast strains. Make sure and do a little research before deciding on a yeast. Manufacturers usually recommend grape varieties that will ferment well with the strain, along with basic fermentation kinetics, condition requirements, and expected aromas/flavors. Just keep in mind that these recommendations are based off their research; there is still a lot of unknown variables in fermentation that can lead to significantly different outcomes.