Increasing thermal efficiency in cooking pasta Odd question, I know, please don't bash me. Hopefully somebody can help me get a better understanding on this matter.
Pasta is usually cooked by dropping it in boiling water (either salting water to increase its boiling point and salt pasta or salting it later on, but I am not sure if there is any practical difference), keep it in boiling water that's still rolling boiling for some minutes and then draining it out.
Since when draining water you are throwing away water that's still around $90 \  ^\mathrm o$C or close to that, I thought it's not that efficient since that temperature might still allow cooking even if it might take a little bit longer.
Do you know if there are any papers on this subject, as I guess food industry might be interested in increasing efficiency?
Would there be any temperature/time equation I'd used to approximate cooking time and water temperature?
I guess that the components that make up pasta have a temperature range in which they change slightly and hence cook, which probably doesn't go as far down as $40 \  ^\mathrm o$C, however could $5$ minutes $\times$ $100 \  ^\mathrm o$C be equivalent to say $7.1$ minutes at $70 \  ^\mathrm o$C or an amount of time that fits the temperature dropping curve of a boiling pot of water from $90 \  ^\mathrm o$C to $60 \  ^\mathrm o$C?
Thank you
 A: 
Increasing thermal efficiency in cooking pasta

I'll assume you mean 'use less energy to obtain the goal of properly cooked pasta'.
There's a variety of things you can do.


*

*Boil less vigorously. A 'rolling boil' is generally advertised for cooking pasta but boiling less intensely will save quite some energy.

*Use less water. The amount of energy needed to bring the water to the boil is proportional to the amount of water.

*Part-insulate the pan: use the pan's lid and wrap it in a kitchen towel. By reducing the outward flux of heat, energy is being saved.



Pasta is usually cooked by dropping it in boiling water (either
  salting water to increase its boiling point and salt pasta or salting
  it later on, but I am not sure if there is any practical difference),
  [...]

Dissolving  stuff (like table salt) in solvents (like water) does slightly increase the boiling point (BP) but the effect is small. The BP of sea water is only a measly $0.5\text{ Celsius}$ higher than that of fresh water.
A: I'll try to provide an answer which, in addition  to provide information for the original poster could help those thinking that this question should be closed that beyond the practical problem there is some genuine theoretical and experimental physics.
Dried pasta is made by flour, salt and water. For some special pastas also eggs are added. After mixing the ingredients pasta is shaped in the desired form (spaghetti, maccheroni, and many other shapes) and dried in order to remove water until the water content goes below 12.5%.  
The cooking process is an interesting physical processes made by three
steps:


*

*rehydration of the dried pasta. This is a diffusion process which re-introduces water molecules. As any diffusion process is controlled by temperature, the highest is temperature, the fastest is the diffusion;

*gelatinization process of starch where a sol-gel transition is triggered in an interval of temperature starting in a range  from 60 °C to 70 °C;

*denaturation and coagulation of gluten starting in a range  from 70 °C to 80 °C.


Therefore, temperatures lower than the water boiling temperature are possible, but not much below 80 °C. Cooking at 80 °C is perfectly possible, although it requires longer times. Moreover it requires larger amount of water to avoid that the sudden immersion of room temperature pasta would lower water temperature much below 80 °C.
As already noticed, adding salt is mainly for taste, since no significant variation of the boiling point can be reached with reasonable quantities of salt.
As far as I know such limiting thresholds connected to the possibility of cooking pasta are well known in food industry and already exploited to make more economic the production process. 
A: When pasta is cooked the proteins need to be raised to a critical temperature, so that the texture comes out right.  I can't find any information on the correct internal cooked temperature for pasta, but bread is typically considered done at ~$190^\circ\mathrm{F} = 87^\circ\mathrm{C}$.  Lets assume that pasta needs to be cooked to the same temperature.
Dried pasta may be partially cooked by the specific drying process (see discussion of effects of temperature on drying process in this review).  Fresh pasta definitely needs to be cooked.  If we take $87^\circ\mathrm{C}$, as the internal cooked temperature.  The water needs to be at least $87^\circ\mathrm{C}$.  You could save energy by heating the water to this temperature and holding it there, rather than boiling it.  This would be like a sous vide pasta. This is a pain to do in practice, as it requires constantly monitoring a thermometer or specialized equipment.
It turns out the boiling point of water is a very convenient temperature to use for cooking.  There are nice visual cues when the temperature is reached, so you don't need to measure.  It's also stable against overheating.  But the boiling point changes with pressure.  Pressure cookers work by raising the boiling point, allowing food to cook at a higher temperature, and therefore faster.  At altitude where the ambient pressure is lower, water boils at a lower temperature, and food cooks slower.
So how long does it take to cook pasta at $87^\circ\mathrm{C}$ instead of $100^\circ\mathrm{C}$?
The equation for water temperature v. cook time for pasta is probably hiding in a table from a camping cooking guide in the guise of altitude v. cook time. The boiling point of water drops to $87^\circ\mathrm{C}$ at about $3650\,\mathrm{m} \sim 12000\,\mathrm{ft}$.  Since the cook time adjustment will depend on the shape of the pasta, it would probably be easier to experimentally determine how long to cook by tasting the pasta regularly than trying to calculate it.
If you are concerned about wasting water, you could boil the pasta in less.  We often cook dried grains, like rice, in just enough water so that all is absorbed.  You could do the same with pasta, but I imagine sticking will be an issue.
A: The biggest heat loss in boiling pasta is the heat carried off by the steam released during boiling. The biggest thing you can do to improve the efficiency of the boiling process is to put a lid on the pan and then lower the heat setting to that which is sufficient to barely maintain boiling. 
