Process for reducing the activity of microbial contamination in a yeast medium

A process for making a medium for a yeast, the process comprising:

• (i) adjusting the pH of a raw medium with a strong acid to provide a first acidified medium having a pH below 4.5;
• (ii) maintaining the first acidified medium at the adjusted pH for a period of time to provide a second acidified medium, wherein the period of time is at least 10 minutes;
• and
• (iii) adjusting the pH of the second acidified medium with a base to provide the medium for the yeast having a pH above 4.5;
• wherein
• the process comprises adding an antimicrobial composition to the:
• raw medium prior to or during step (i), and/or
• acidified medium prior to or during step (ii);
• wherein the antimicrobial composition comprises at least one weak acid, optionally, in combination with an acid stable bacteriocin and/or an antibiotic;
• wherein step (i) comprises adjusting the pH of the raw medium below or equal to the pKa of the at least one weak acid of the antimicrobial composition;
• and
• wherein step (ii) comprises maintaining the first acidified medium so as to decrease the contaminating microbial activity in the second acidified medium, when compared to a corresponding control medium not previously treated with the antimicrobial composition;
• and
• wherein the raw medium comprises a fermentable material.