How do we know it is scattering?

In the experiments with diluted milk in a glass, it was stated that blue light was being scattered more than red and that this explained the apparent colour changes in the glass of milk. But how do we know that it is scattering? In the video, natural light was used to illuminate the milk glass, could the apparent blue colour not just be a reflection of the sky?

To check that the diluted milk really does scatter the incoming light rather than just reflect it, we can do two additional experiments.

Experiment 1: Change the light source

Rather than use natural light to view the diluted milk, wait until after dark, close all the curtains and then use a white light source (some resources online even suggest using a torch). What colour is the milk now? How does the colour change as you rotate your viewpoint relative to the light source?

Experiment 2: See if the light from the diluted milk glass is polarised

If the light coming from the diluted milk glass is scattered by Rayleigh scattering, it should be polarised just as the sky is polarised. Look at the sky through a polarising filter (it could be a pair of sunglasses). Rotate the filter. You should see that the sky appears to get darker and lighter as you rotate the filter. This is because light that is scattered by Rayleigh scattering (the type that produces blue skies) is strongly polarised. If the light from the diluted milk glass is truly being scattered you should be able to discern some level of polarisation from the milk glass (though that polarisation may be very weak owing to the additional scattering by the fat globules that will act to even-out the polarisation of the light that is emitted from the glass). Can you detect any polarisation effect?