Measuring Conductivity of a Liquid

I am trying to design a circuit which will measure the conductivity of a liquid(milk). I am using a microcontroller ATMega128 to perform the calculations. I can create a PWM output and read the input on an ADC. The circuit runs on 5vDC.

I have no idea how to go about designing a circuit which will accurately measure the resistance. The probe is stainless steel and 1cm in distance from each other.

Can someone please help me design a simple circuit that will measure the resistance?

Sources that may help
Electrical Conductivity of Milk:
Ability to Predict Mastitis Status

and

Electrical conductivity - Wikipedia, the free encyclopedia

3v0

Conductivity is 1/R. Just measure the resistance and use it to calculate for conductivity.

Boncuk