PHOSPHORIC ACID

PHOSPHORIC ACID 75% is a clear solution made from food grade phosphoric acid and is used in the brewing industry for acid washing yeast.

Principle
Acid washing is a tool that brewers use to eliminate contamination bacteria from pitching yeast. Acid washing kills bacteria with minimal harm to the brewing yeast, providing that the process is carried out correctly. The effectiveness of the process relates to the time and temperature it is carried out, at and the pH achieved.
NOTE: Acid Washing will not remove wild yeast.

Method of use
Preparation is essential. Ensure that you have the yeast and the acid fully chilled as the wort nears the end of boil, and start the washing process at this time. The washed yeast will then be ready for pitching when the wort is cooled.
Do not be attempted to wash yeast on a quiet day when you are not brewing. Viability of washed yeast will fall markedly as storage time increases.

DO’s of acid washing:

Use food grade phosphoric acid, diluted about 1 in 10.
Chill the acid and yeast below 5 °C before use.
Ensure that the liquids are stirred together well so that there are no areas of higher acid concentration.
Ensure pH lies between 2.0-2.2
Pitch yeast after set time of 1 hour

DON’TS of acid washing:

Don’t deviate from temperature, time and pH limits indicated above
Don’t store washed yeast
Don’t wash “unhealthy” yeast (yeast which has been stored for long periods, heavily contaminated yeast, yeast from slow fermentations.) If it is essential that such yeast is washed, use a high pH value for the wash (pH 2.3 - 2.5) and or shorter contact times 30-60 minutes) until the yeast has been used to pitch one or more fermentations and recovers full activity.
Don’t (or at least try to avoid) washing yeast from very high gravity fermentation (>8% v/v ethanol).