After getting everything organized (equipment, staff, etc.), yeast propagation can began. As mentioned previously, timing is one of the most difficult parts of yeast propagation. This guide is written in regards to yeast propagation for white juice, but the primary difference when dealing with red juice is that yeast starter creation uses saignee.
If possible, I like to have a stock of juice designated solely to creating yeast cultures. This can pose several different issues depending on how the winery operates. Larger wineries will be more successful including this in their yeast propagation program, which will in turn help streamline the production process significantly:
Since most wineries won't be able to commit to the above, I will discuss propagation on a batch-to-batch level. Feel free to contact me to discuss propagation for larger wineries.
My experience with yeast propagation shows an average inoculum volume of 1-2%. This means the volume of inoculum is 1-2% of the total volume of juice to be inoculated. In smaller scale propagation procedures, this will likely not be achievable for several reasons, Aiming for a 5-10% inoculum volume may be advisable.
Once the juice to be inoculated is clarified, it will arrive in its fermenting tank. A small portion of this juice should be transferred to a yeast propagation tank, ideally via heat exchanger to arrive around 25° C (77° F).
The yeast starter juice should be prepared for fermentation in a similar fashion as any juice to be inoculated.
Once prepared and inoculated, the culture can then be left for several hours. Depending on time constraints at the winery, 6-12 hours is a good period of time before the first round of analysis. Determining the analysis schedule moving forward can be based on the progress during this first time frame.
Cell count is the most essential measurement, but I also like to have brix, pH, and VA checked to ensure everything is going well. Sensory evaluation is also a must.
This is when experience with yeast propagation becomes increasingly important. Knowing how to balance all the variables involved to reach the end goal of inoculating the juice to be inoculated at the correct temperature and inoculating rate is a lot easier said than done. The balancing act becomes exponentially more difficult once you begin talking about multiple inoculations from a single culture on top of the timing of everything.
Here are a couple situational examples assuming that the culture is not sufficient for inoculation:
Determining when the culture is ready to be used for inoculation depends on several variables.
Inoculation is rather simple. The yeast starter needs to be transferred into the juice to be inoculated tank and mixed through. Just keep in mind that yeast populations are constantly changing within the yeast starter, so all processes are time sensitive. After inoculation, the fermentation can be tracked as per usual.