I have a real concern about using the pressure cooker as described in Slope-soarer's post. As long as youhave liquid water in the pressure cooker, at the relief pressure the temperature is limited to about 250 deg F. However if you vaporize all of the liquid water then you no longer have the temperture limitation of a water/steam system. As soon as the liquid water is vaporized the temperature will start to increase and the pop off valve will no longer be venting until you start to replace the water vapor with organic vapor from the oil. Since most of these type of oils have boiling points in excess of 300 deg F the temperature can get very high. The yield strength of aluminum ( which most pressure cookers are made from) begins to decrease rapidly at temperatures above 300 deg F. I am quite concerned that this has the potential for a catastropic failure of the pressure cooker.

What I would suggest is that you continue to use an open pot, however when the frothing has stopped(which means the liquid water has vaportzed) then use a candy thermometer to take the temp of the mix up to about 350 deg F and hold it there for about a half hour.