Acid Washing Yeast - Lievito Madre?
In professional brewing, there is a yeast handling technique used that is known as acid washing. The procedure is to subject the yeast to a low pH (2.1) for a period of time, typically 1-2 hours, at a temperature of 4C. The pH is normally lowered with food grade phosphoric acid. The yeast is then pitched into the wort.
The reason for doing this is to kill off bacterial contamination, but leave the yeast relatively unharmed. Mainly it is to kill off the aerobic bacteria, eg Hafnia, which are implicated in the production of potentially carcinogenic nitroso compounds. But there is also a reduction in other bacterial numbers, eg Lactobacillus.
So I got to thinking: could this be be a fast track route to a Lievito Madre? Ie acid wash some starter and do a couple of refreshes and it might be good to go! Who knows?
Of course phosphoric acid is rather nasty stuff, and appropriate PPE is required, but I believe that citric acid can also be used.
Just some food for thought!