|Syrah yeast. There are hundreds of different types of yeast that can be used|
to ferment must into wine. We used about a dozen varieties this year.
The liquid yeast is poured into the tanks and bins, and this procedure is called "inoculation". The yeast cells then process the sugars in the must into CO2 and alcohol. And herein lies the difficulty in making wine: As the level of alcohol rises, it kills the yeast. As the sugar gets depleted, the yeast cells run out of food. If the temperature rises too much, the yeast dies. If the temperature is not high enough, the yeast doesn't process the sugar. If the pH isn't just right, the fermentation can be affected. And so on... It's a pretty delicate process, and getting it right isn't so easy.
The amount of alcohol that is produced by the yeast is directly proportional to the sugar content of the must, and since we crushed very ripe grapes we often had to add water to dilute the must. Too much sugar will create too much alcohol, which will kill the yeast before the fermentation is complete (but we have a secret weapon to fix this problem). Sometimes, the fermentation can be re-started once the wine has been transferred to barrels:
I'll post a few more things about yeast, most notably a little something about some very special yeast that we use in desperate cases. Stay tuned...