Once you know the budding index, how can you use the data?
The budding index represents the proportion of cells that are multiplying within a given cell population. For example, if the budding index is 20, this indicates that 20% of the identified cells were in the process of budding at the time of analysis.
As budding is the primary means of reproduction in S. Cerevisiae, which is the most commonly used yeast for alcoholic fermentation in wine production, monitoring the budding index allows for tracking the yeast multiplication process during fermentation. This is important because a healthy multiplication process is a sign of a healthy fermentation.
According to Tony Balzan (personal communication, December 5th, 2019) from yeast producer AB Biotek,
“The number of budding yeast cells can tell us a lot of what is happening during fermentation. Firstly, during the early stages of fermentation, a high budding percentage is indicative of good start yeast vitality and a healthy fermentation. Early on, we are expecting our cell sizes to be smaller as young daughter cells quickly initiate new cycles of replication. As fermentation progresses and environmental stresses increase (e.g. ethanol concentration and low pH) yeast energetic status deteriorates and the budding percentage will drop. By the end of fermentation, single cells become noticeably larger as yeast move into survival mode, while the budding cell percentage becomes very low.”
The lag phase is the period between yeast pitching and active fermentation and it is when the budding index is most useful. During this phase, yeast adjusts and transitions from dormancy to active fermentation, which typically occurs within 12 hours but can range from 1-24 hours.
During this phase, the budding index provides valuable insight into the fermentation process, including whether enough yeast was pitched, if the must is properly oxygenated, and if the must temperature and nutrient levels are providing yeast what it needs in order to enter the exponential growth phase.
As the budding index is influenced by various factors such as yeast strain, fermentation stage, and time from inoculation, there are no specific reference values. However, by establishing a baseline for successful fermentation, you will be able to predict the expected budding index at various stages of fermentation for future batches.