Consider using ultrasonic flow meter. This way there will be no contact between milk or other fluids and the measuring gear. More than that you can replace the faulty unit without dismantling the equipment since it is placed outside of duct.

try a glass rotameter, is simple, shiper and precise enough for liquid with bubles, just the right density need to be used.

You can use different mesh size in order to break bubbles. You just have to focus on right velocity and density.

try this link. https://www.alibaba.com/showroom/milk-flow-meter.html.

Mr. Bishwajit Sharma is on target to focus on the bulk fluid density, and doing so by breaking up the bubbles with the goal of having a more-or-less homogeneous fluid. Venturi meters with sanitary seals is a good direction to go.

Milk analysis is very complex, and not for the reasons most engineers think.

I've actually designed and sold dairy milk analyzers and systems.

I used Doppler for the velocity of the milk. (if the flow is too fast then the milk fat droplets breaks into smaller droplets and the milk tastes flat; too slow and the fat agglomerates and the milk tastes greasy.)

Also, you want to determine the density (from the speed of sound in the milk) and measure the scattering to make sure that the droplets of milk fat are in spec., homogenized properly not separating.

As for bubbles, they will help with the Doppler measurement and although they contribute to the attenuation, you won't really see much effect unless it's a foam.