The propagation of selected yeast strains

When using selected starter cultures for the fermentation of a must, it is recommended to use cleared must from healthy grapes. For the production of fruit or berry wines the respective fruit or berry must is used. Sweet juices available in trade are also suitable for this purpose.

For 10 liters of must, 2 - 300 ml of the Geisenheim pure yeast culture is needed. The added starter culture is distributed inside the must by good shaking and is then left to ferment at room temperature. 2 or 3 liters of this starter culture are sufficient for the fermentation of 100 liters of must.

If fermentation of larger quantities is required, then the first starter culture must be further propagated. This happens by adding double or triple quantity of must. When this starter culture ferments, it can be directly used or further propagated.

For these purposes, it is recommended to use at least the double quantity of starter cultures, i. e.  4 - 6 %, in difficult cases even up to 10 %. The corresponding volume is grown by in steps addition (doubling the volume). The problem must is added in the last step. Before adding the selected starter culture, the must with stuck fermentation should be filtered first.

When fermenting a wine to a higher alcohol content, the propagation can also be performed in must. The last propagation step must happen with the to be fermented wine. In case this wine has already fermented to dryness, 25 - 30 g/l sugar must be added when adding the yeast. Only when the starter culture ferments, it can be added to the to be fermented wine in the above mentioned concentration. The fermentation of wine is slower than the fermentation of a grape must. Stirring several times accelerates the fermentation process substantially.

5 liters of mash are mixed with the delivered yeast starter culture (100 - 200 ml) and are left for fermentation at room temperature. When  fermentation is noticed the same or double quantity of mash is added and so on. 2 - 3 % of the propagated yeast is sufficient for the fermentation of fruit mash. For better liberation of CO₂ the mash can be stirred during fermentation.