De-aerated fuel
JammedStab
...Jet fuel contains dissolved air and the amount depends on the temperature of the fuel and the altitude. As the airplane climbs to cruising altitude, and the ambient pressure decreases, air is liberated from the fuel as bubbles that rise to the surface..
On one past passenger aircraft with a high climb rate, those tanks where the fuel remained relatively static during the climb required the fuel to be de-aerated to ensure the air in solution in the fuel did not become a hazard as the ambient air pressure in the fuel tanks decreased during the climb.
There were two principal areas of concern. Firstly, that as the air in solution in the fuel expanded, the likelihood of fuel pump cavitation increased, and secondly, the possibility that transient spike increases in fuel tank pressure might lead to fuel transfer and loss via the vent system.
De-air pumps were used, which circulated fuel through spray nozzles within the tanks, and, at higher altitudes, the tanks were partly pressurised to counteract these concerns and also to counteract the effects of kinetic heating on the fuel and so prevent the lighter elements of the fuel boiling off.
noflymore
... the more volatile elements (benzene, naptha, toluenes etc) in an oil based fuel are stripped from it ... by heat ... leaving the heavier fractions behind...
Our ground engineers had another word for the “heavier fractions” you mention that could be left behind in our very thin tip tanks, due to kinetic heating and low ambient air pressure boiling off the lighter elements, if the poor F/E forgot to use that fuel as soon as practicable!