noun. A state of or tendency toward being acidulous or somewhat sour or acid.

noun. the taste experience when something acidic is taken into the mouth

"When boiled in milk, it gives off its acidulousness to the whey; and either this whey, or the expressed juice of the plant, much diluted with water, may be used as a good refrigerant drink in fevers."

acidulously  

sour  sourness  tartness