Is the aluminium foil usable in this condition?
That's just aluminium oxide (Al2O3) and it's harmless as:


it's insoluble in water
it's nearly insoluble in alcohol.
is very hard (Basically the same material as a ruby or a sapphire)
it's chemically nearly inert
Is basically the same substance as the non-shiny side of the Aluminium foil


So it's definitely useable for all intents and purposes. (including cooking ;-) )