When it comes to determining the appropriate amount of active dry yeast for a one-gallon batch of wine, there are a few factors to consider. While most yeast manufacturers recommend using a 5 gram packet for 1 to 5 gallons of must, it is possible to use the entire packet for a one-gallon batch with successful results.
In my personal experience as a brewer, I have found that using the entire 5 gram packet of dry yeast for a one-gallon batch yields excellent fermentation. The yeast is able to fully ferment the sugars in the must and produce a clean and balanced wine. However, it is important to note that each yeast strain may have different recommended usage rates, so it is advisable to consult the specific instructions provided by the yeast manufacturer.
Dividing a 5 gram packet of yeast into smaller portions for multiple one-gallon batches can also be successful, as you have mentioned. This method can be particularly useful if you want to experiment with different yeast strains or if you have limited access to yeast packets. By using a quarter of the packet for each batch, you can still achieve a healthy fermentation and produce four distinct wines.
It is worth mentioning that the yeast population and fermentation kinetics may vary slightly between using a full packet versus smaller portions. When using a smaller portion of yeast, the initial yeast cell count may be slightly lower, which can result in a longer lag phase before fermentation starts. However, once fermentation begins, the yeast should multiply and ferment the must just as effectively as when using the full packet.
Ultimately, the decision of whether to use the entire 5 gram packet or divide it for multiple one-gallon batches depends on personal preference and the specific yeast strain being used. It is always a good idea to follow the instructions provided by the yeast manufacturer, but don't be afraid to experiment and find what works best for you.