In our image, we think that something with a low pH (acidic) is sour. Example: lemon vinegar However, although sourness is greatly affected by hydrogen ions, the strength of sourness does not necessarily correlate with the strength of pH. Example: Carbonated water has a pH of 5 or less but is not sour That said, humans tend to perceive foods with a low pH (acidic) to be palatable, and foods with a high pH (alkaline) to be unpalatable. It is generally felt that pH is between 4 and 6. Conversely, when the pH becomes high (alkaline), the taste becomes dull and unappetizing. Adding lemon juice (pH 2.1), vinegar (pH 3.0), soy sauce (pH 5.0), etc. to lower the pH is described as ``tightening the taste''. Also, there is a characteristic that the sourness is felt as a taste in the same way in any temperature range.
From here on it's subjective. When I go to an izakaya, I often order lemon shochu high. Especially when you drink it while eating greasy food, it makes your mouth feel clean and delicious. This is because sourness is a taste that does not leave an aftertaste in saliva, but when it disappears, it has the effect of erasing the aftertaste of other flavors as well.