Making a Starter Culture
Liquid yeast cultures can be expanded to inoculate larger volumes of must. A small volume of liquid culture from Wyeast Laboratories can be added to a small volume of must and allowed to ferment for 24 to 72 hours. This must can then be used to inoculate a larger volume of must.
- To create a starter culture one must first determine the final volume of must that will be inoculated. The initial inoculum should be 0.5% of the total volume of the starter. For example: 1 liter of liquid yeast from Wyeast would inoculate 200 liters of must. This will result in a cell count of about 6.0 x 106 cells per ml.
- Determine a propagation schedule to achieve the desired final volume. Subsequent increases in volume should be in the range of 10 to 20 fold. For example: 1 liter of liquid yeast from Wyeast inoculates 200 liters of must, incubates for 72 hours, and then in turn inoculates 2000 liters of must.
- Create initial starter culture. Incubate for 24 to 72 hours at 65° to 75°F (18° to 24°C).
- Inoculate next or final volume of must. Incubate for 24 to 72 hours at 65° to 75°F (18° to 24°C) if increasing in volume again or set to desired fermentation temperature if at final volume.
- Aeration or oxygenation of the starter is essential for the production of healthy yeast. Oxygen is used by the yeast to produce sterols which are necessary for yeast growth. Oxygenation of must increases the final cell density and improves the long term health of the yeast culture.
It is important to understand that creating a starter can increase the risk of infection by undesirable organisms. If non-sterile must is used, then there are other organisms present that could multiply to unacceptable levels. Use of either heat sterilized or sterile filtered must or juice is recommended. Use of a broad spectrum yeast nutrient is recommended for best results.