interesting idea, but the title of this thread is still misleading.
Theoretically, totally possible. But not in your standard pressure cooker.
Pressure cookers create their pressure using the expanding water vapour.... meaning, the temperature is already extremely high just to achieve a pressure of 2 atm. Mine reaches around 120C at 15 PSI, which is 250F or 393K.
This is very hot. There is no way in hell you can get super critical CO2 with temperatures like that. Satan doesn't decaffeinate his coffee. He has no need for supercritical CO2
What you are describing has nothing to do with supercritical, or 'critical' CO2. The water is doing all the extracting.
like suggested above, it is an interesting idea, since carbonated water has a lower pH. Although, keep in mind, even distilled water has a low pH, usually around 5, due to dissolved CO2 from the atmosphere.
But your not even close to passing the critical point of CO2. Which is why the title is misleading
Your understanding of gas laws is a bit skewed. I myself, use a pressure cooker to extract my MHRB, its fast and effective, I use dilute vinegar cook at 15 PSI. This seems to effectively extract the alkaloids at a much faster rate then just boiling.
Pressure cookers can reach around 2 atm, to use CO2 as a solvent, you need a LOT more then that to pass the critical point, more like 70 atm at 300 Kelvin. You can't do this with a pressure cooker, since the temperature is also increasing proportionally with the pressure.
Unless you had a tank of CO2 feeding gas directly into the system, and a pressure cooker capable of very high pressures, and some way to remove the heat energy being relased. (Just as releasing pressure causes a drop in temperature, pressurizing causes an increase. Its exothermic. You can actually feel this effect if you put your hand on the cynlider of a bicycle pump and start pumping, or the reverse with a can of N2O) Then you could dissolve more and more CO2, and if you were able to reach the critical point in temperature and pressure. Then it might be possible. otherwise you can't extract anything with the CO2 behaving as a solvent.
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Also, pressurizing the sparkling water isn't going to do anything.
For instance, if you bought this product to keep your pop fizzy, your an idiot.
Oh, and here is a graph that might help your understanding on what kind of temperature pressure ratios you would need to get into the supercritical range of CO2, the area past the critical point.
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