In photoshop generate some clouds. Up the contrast with levels.
The more white areas the more lumps of powder you will have.
Add a gradient ontop to create the 'full' part of the bottle.
Depending on how defined you want the edges you can apply gaussian blur.
Create a second glass material, set the diffuse to white/whatever colour your powder is and plug the map you created into the refraction colour slot.
Duplicate the inside faces of your bottle and scale them to 0.99 as mentioned above.
Apply the masked glass material to the inside faces and the normal glass to everything else.
Ive attached the map i made for reference and a render to show what it does.
Good luck!