I would not reuse that oil. The frying-oil reuse that occurs in fast food chains is reuse for the same day or over just a few days. They also store it properly and not just sitting exposed in the fryer.
justkt is correct that more saturated fats are less sensitive to breakdown, this is why bacon grease can be kept for a rather long time.
Three factors play a significant role in oil degradation:
Oxidation
Any contact with air causes oxidation in oil. High temperatures, metal alloys, surface exposure, and even UV light act as catalysts to this reaction.
Hydrolysis
When water interacts with oil it causes it to taste tainted or acidic. This is exacerbated by high temperatures, heating/cooling cycles, and oxidation products.
Polymerizaton
When frying oil deteriorates, the resulting products form both volatile (or reactive) and non-volatile compounds. Non-volatile compounds remain within the frying oil, and can produce polymerization at frying oil temperatures above 200°C (390 F) or in isolated hot spots within the frying system. These molecules bond together to form large, different-sized clusters that accumulate on the oil’s surface. Since they don’t dissolve, they cause foaming; trapping air under the oil, and increase the possibility of hydrolysis.
Given all these, the best environment for any oil is an cold, dark, airtight place. Cold temperatures may cause clouding, but this is not a cause for worry.
Source:
http://www.heatandcontrol.com/technical%20articles/Maximizing%20Cooking%20Oil%20Life.pdf
Unless you are prepared to build some industrial strength equipment of your own design and then move everyone in the neighborhood away while you experiment with this, I fear you are taking your life in your hands.
Normal pressure cookers add a maximum 15 PSI to achieve a water boiling point of 121 C or 250 F. Autoclaves, used for surgical sterilization, go to 30 PSI. You are talking about going more than twice that.
There is no reason, based on the science of Maillard reaction, to believe that it would not occur at a high enough temperature. The presence of excess water would normally inhibit the process because of temperature reduction, but your "super duper pressure cooker" would keep the temperature at a high enough level to allow the chemical breakdown to occur. You might, in fact, discover that it occurs a bit earlier, as water tends to facilitate many reactions. Caramel making comes to mind as an indicator of what might be achieved, as sugar syrup (OK, most of the water is gone, but in principal) browns when you get in the above 330F-165C degree range.
As to crisping based on quick pressure reduction (perhaps when your device explodes?) That seems less likely as most crisping comes at the loss of water, and you are, in effect, keeping water in contact with your food both in liquid and superheated steam form. It would, most likely, be similar to a braised food surface, than a fried one.
Interesting thought. Please don't try this.
Best Answer
If there is one statement that you will read here over and over again it is:
Use a thermometer to determine the doneness of your meat.
There are many "formulas" depending on bird weight, cooking method and - frankly - gut feeling of many cooks, but for a formula to reliably work you would have to factor not only the weight of the bird, but also starting temperature of the bird, build (lean? chubby?) of the bird, temperature of your oven or frying oil, the heating ability of your oven or fryer or, beware, the coals you are roasting the bird over and almost everything else except the lunar phase.
Is this possible? Sure, and I guess some weird physicist1 has developed and possibly even posted it somewhere. Do you want to do the calculation when you are preparing side dishes or isn't it easier to poke a thermometer in the bird's breast and thigh and be done with it?
The formulas serve to give you an estimate of how much time you should need for a bird - give and take a bit.
So to get a ballpark number according to Paula Deen:
Start meassuring a bit before that and remove your turkey when it has reached 150-155 F, carry-over cooking during the subsequent thirty minutes resting time should let the bird comfortably reach the target temperature of 165 F.
1 No offense to hard-working physicists - I picked just the first cliché that seemed to fit.