How can you use the data provided by the histogram of cell size?
The histogram of cell size provides insight into the distribution of cell sizes within a sample. Typically, with wine yeast, you would expect to see a range of sizes between 6 and 10 µm. By monitoring the histogram during the fermentation process, you can observe the evolution of the cells.
Usually, an increase in larger cells indicates an aging yeast population as the cells grow larger with each budding. As outlined in the article on the budding index, cell sizes are expected to be smaller at the start of fermentation, and larger by the end.
Evaluating the cell size of your yeast population can provide valuable information about the duration of the transition from dormancy to fermentation and the yeast’s performance throughout the entire fermentation process. This is because research has demonstrated that the age of the cells can affect the rate at which sugar is utilized during fermentation (with virgin, smaller, cells being slower to begin utilizing sugars), which can have a significant impact on the entire fermentation, but especially on the lag phase*.
It was also observed that older cells, which are typically larger, tend to be more efficient at flocculating. This is particularly relevant when harvesting and reusing or propagating your own yeast, as the distribution of cell sizes within the yeast population can provide an indication of how well the yeast will flocculate.
Additionally, other studies have revealed that larger yeast cells may have a higher concentration of ergosterol in their cell membrane, which increases the yeast’s resistance to ethanol. As yeast cells age, the content of ergosterol and unsaturated lipids increases, providing protection from the increasing alcohol concentration during fermentation. This can be particularly useful when attempting to fix a sluggish or stuck fermentation by adding more yeast. In this case, selecting a population of larger yeast cells increases the chances that the yeast will not be immediately killed off by the ethanol present in the tank.
*The lag phase is the period before yeast is added to the must and the moment fermentation has begun.