„i.d.m.“ is the abbreviation for „in dry matter“
The dry matter is the substance which remains when water is withdrawn from the cheese. The fat content in dry matter is independent from water content or ripening period, while the „absolute fat content“ will vary during the ripening stages due to evaporation.
You may roughly calculate the “absolute fat content” in cheese with this formula:
Hard cheese fat i.d.m. x 0,7
Cheese for slicing fat i.d.m. x 0,6
Soft cheese fat i.d.m. x 0,5
Fresh cheese fat i.d.m. x 0,3
„Coburger Bio-Butterkäse 50%“ (cheese for slicing) for example contains 50 x 0,6 = approximately 30% fat.