This article presents a multi-resonant sensor (double band) that uses open ring resonators (SRR) to detect milk adulteration with water. The sensor has a dual resonant frequency of 2.5GHz and 3.5GHz using an industrial, scientific and medical (ISM) band. This sensor was implemented on Rogers substrate using a single port. The process of detecting milk adulteration (i.e. milk with water) was performed by immersing the sensor in different samples. With the displacement in resonance frequency a numerical model was developed that allows relating the physical characteristics of the milk, which were mass density and viscosity with the dielectric characteristics of the milk. The proposed sensor is of low cost, easy implementation and manipulation.