the world > physical sensation > taste and flavour > sourness or acidity > [noun] > souring (3)
The process or fact of becoming or making sour.
The action of becoming acid or sour; a tendency to become acid or sour; the process of acetous fermentation. Also: acidity, sourness. In later use…
The state or fact of being acidulated; the action or process of becoming or being made more acidic; an instance of this. Also figurative.