Why does this milk take a long time to set as curd?

Explanation

1) Curd form from the milk by the action of Lactic acid produced by bacteria in the milk.
2) If milk man add Baking soda `(N/AHCO_3)` to the milk it neutralise acid, which is produced by the bacteria.
3) Excess acid is required to change the milk as curd.
4) It takes long time