Problem: Bacteria in the pitching yeast. Acid washing can help to reduce the number of some bacteria, but is not a complete solution. We usually do not recommend acid washing because:
Acid washing only reduces the number of bacteria, but does not completely remove them. After one or two more generations, the bacteria can regenerate up to numbers that affect flavor. Acid washing has different effects on different yeast strains, and usually reduces the quality of their performance and viability. Acid washing is not an effective way to kill wild yeast.

However, if acid washing is done, here is an effective method:

1. Keep the yeast between 36-40oF.
2. Determine how much yeast will be needed to pitch, put in a stainless container and begin the acid washing procedure 90 minutes before the yeast will be pitched.
3. Add food grade phosphoric acid until the pH of the slurry is between 2.0-2.5. Mix thoroughly to get an accurate reading.
4. Let the mixture sit for 1 hour at 70-75oF.
5. Add the entire mixture to the fermentor.

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