Hi there,
Hope you are doing good.
Yes, there is an acid named "Lactic acid" which is responsible for the sourness of the milk. The same acid is produced in muscles during exercise.
- If there is a lack of oxygen in our muscle cells, pyruvate breaks in a different pathway. Glucose (a 6-carbon molecule) breaks into pyruvate (a 3-carbon molecule) and pyruvate is then converted to lactic acid (a 3-carbon molecule) along with the release of energy.
Glucose -->pyruvate + energy --> lactic acid + energy.
Regards