The problem is that when you release pressure on anything but water, as the CO2 starts to come out of solution it bubbles up and tends to spill out of the bottl

The problem is that when you release pressure on anything but water, as the CO2 starts to come out of solution it bubbles up and tends to spill out of the bottle. I'm sure there is science on this but my naive guess is that this is partly because theres more nucleation sites to bubble more, and then the non-water fluid will "soap" up a bit for lack of a better description (form bubles) causing it to then spill up and out. You can get around this by releasing the pressure slowly. Some models of SodaStream (e.g. the Source) let you do this and others do not (e.g. the electric model). As a secondary concern if the fluids do spill up out of the top into the valve area, it gets stuff on the seals etc and it doesn't seal as well later. Lower pressure = less carboned. And it's very easy to do this even releasing the pressure slowly. So; yes.. but.. no. If you want to do that regularly, you're better off making some other kind of solution I think. It's pretty easy to make your own rudimentary sodastream. (and as others stated, they specifically tell you not to do this)