Is Dahi Thermophilic or Mesophilic?
Traditional Foods: General and Consumer Aspects page 103:

As specified under the Food Adulteration act of 1955 (India):


  Mild dahi is made from mesophillic lacto cocci such as...
  ...Sour dahi contains additional cultures belonging to the thermophilic group.


Looks like there's a lot more info in the link, including typical prep methods.