Tips for Avoiding Fermentation Lags
The incidences of unexplained and undesired fermentation initiation problems can be reduced by:
- Use of a microscope to monitor populations: microscopic examination of the fermenting must or juice can determine if high populations of bacteria or apiculate yeasts are present. If they are, then fermentation conditions should be selected to minimize the inhibitory impacts of these populations.
- Knowledge of nutrient levels: severe nutrient limitation can lead to a slow or protracted start of the fermentation. However if the limitation is severe enough to impact initiation it will also likely lead to an arrested fermentation. Measuring juice nitrogen levels is important and then adjusting those levels to match the requirements needed to attain dryness at the starting Brix level is important. At 21 Brix a yeast assimilable nitrogen concentration of 200 mg N equivalents/L is sufficient with 120 being absolutely required for completion even by low-N requiring strains. At higher Brix values more nitrogen is needed. At 25 Brix 300 ng N/L is needed and above 28 Brix, as much as 400 ng N/L may be required, depending upon the strain. Even higher nitrogen levels may be needed if the nitrogen is added late in the fermentation after the step of nitrogen transport becomes inhibited by ethanol.
- Care in sulfite addition: a major cause of long lags under commercial conditions is error in sulfite addition levels. This is an important step and care needs to be taken in how the solutions are prepared and added.
- Avoid extremes of temperature: super cooled or heated juices should be equilibrated to the desired fermentation temperature before inoculation. A temperature shock early on, if severe enough, may impact the ethanol tolerance of the culture later on in fermentation even if arrest did not occur.
- Use proper rehydration techniques: the rehydration of yeast is not a step at which to take short-cuts. Manufacturer’s instructions should be followed as some yeast require special conditions for optimal rehydration. Poorly rehydrated yeast may have appeared to historically conduct fermentations without difficulty but these fermentations may have been conducted by the native winery flora, by cross contamination with other tanks or by the survivors of the packet used. But there are times when poor rehydration is the cause of a sluggish start of the fermentation.