Frequently Asked Questions About Wine Yeasts
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Why is rehydrating the dry yeast before pitching important?
Dry yeast needs to be reconstituted in a gentle way. During rehydration the cell membrane undergoes changes which can be lethal to yeast. In order to reconstitute the yeast as gently as possible (and minimize/avoid any damage) yeast producers developed specific rehydration procedures. Although most dry wine yeast will work if pitched directly, it is recommended to follow the rehydration instructions to insure the optimum performance of the yeast.
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Does foam or no foam during rehydration give me an indication of how actively the yeast will ferment?
No! There is no definite explanation why some dry yeasts foam more than others but it has been proven in a series of tests that the occurrence of foam during rehydration is not an indication for more active yeast. Yeast that produced large amounts of foam could have poorer activity than yeast that did not produce any or only small amounts of foam.
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Should I refrigerate or freeze my dry yeast until I use it?
Yes, although dry yeast can be stored at room temperature and performs well for the duration of the shelf life it is preferable to store it at colder temperatures. Dry yeast will always lose some of its viability and activity over time but at colder temperatures these losses are less than at warmer temperatures. If you choose to freeze your dry yeast for storage, let it warm to room temperature in the package before rehydration & pitching.
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What will happen to my wine if I add too much or too little yeast?
The pitching rate influences the lag phase and general fermentation speed as well as the flavour of the finished wine. Too low pitching rates will result in longer lag phase and higher risk of contamination as well as longer overall fermentation time (and sometimes stuck fermentations). Too high pitching rates speed up the fermentation but can lead to early autolysis.
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Do I need to use nutrients when using dry wine yeast?
Like any yeast, dry wine yeast can benefit from additional nutrients.
I have a package of dry yeast that is 6 months past its expiration date. Can I still expect it to work?
Although the yeast might still be viable and active, there is no guarantee that it will perform as well as yeast within its expiration date.
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How does changing the fermentation temperature change the “dry” or “fruity” character of my wine?
At warm fermentation temperatures, more esters and higher alcohols are produced than at colder temperatures, resulting in more fruity, floral flavors.
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Can you mix strains in a fermentation?
It is not a good policy to mix strains since there is too much uncertainty. Each strain has its own lag phase, growth rate, oxygen and nutrient requirements. Each strain reacts slightly different to temperature and pH. It’s very important to know the possible synergies or antagonism between the 2 yeasts as it will influence the dynamic of population .Some strains have the competitive factor or are quicker to take in the nutrients. Some are sensitive to the factor while other strains are immune to the factor. It is possible to make a 50/50 blend inoculation and with in 48 hours find only 100% of one of the strains.
If you are doing this to achieve more "complexity" in the final wine, a better way is to divide your juice into separate fermenters and then ferment each selected strain separately. You can determine the fermentation characteristics and flavor and aroma profile of each strain separately, and then blend the finished wine to your taste. This is a more reliable way to achieve the benefits of a mixed fermentation.
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What does the phrase “competitive factor” refer to?
Wine yeast may contain proteins which allow them to prevent other yeasts from competing during the fermentation. For this reasons these Proteins are called Killer toxins, not as scary as it sounds unless you are yeast that does not contain another factor that can protect the yeast from the killer toxin. Generally speaking wine yeasts can be killer positive (contain the toxin), killer sensitive (no toxin and are killed by the toxin) and killer neutral (no toxin and are not killed by the toxin). These systems are common in biology and the toxins themselves tend to be specifically active against other yeast. Bacteria and humans tend not be affected by yeast killer toxins.
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Can an open package of dry yeast be resealed and used later?
It is possible, but the important factors are air and moisture. If you can vacuum seal the yeast then this would be ideal, otherwise a re-sealed pack should be used quickly as the cells will lose activity in the presence of air and water. Pressing a pack tightly before applying the seal is not really that effective. Use opened yeast within a week to ensure good performance.
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Will SO2 additions affect wine yeast?
Some yeast will be more sensitive to SO2 than other yeasts. In general high SO2 additions may be used to stop the yeast fermentation once the fermentation is complete and the yeast are already in a weakened state.
*This content is adapted from Lalvin/Lallemand’s website for Wine Yeast - For more information and technical data visit Lalvin-Lallemand's website
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