Among cider geeks, there's a stated preference for 316 over 304 due to it's higher corrosion resistance. Corrosion pits = bacteria hiding places.
(I ingnore the advice, btw - 316 is too expensive for me)
I was curious, so I asked the metallurgist down the hall. (I'm a chemist during the week - my office is in front of one of the metallurgy labs.)
I described the types of contacts for beverage use as citric acid solutions (about pH 3), sodium carbonate caustics (about pH 9), SO2 at up to hundreds of ppm, possibly Cl at a few hundred ppm, steam, alcohol, light (low carbon number) acid and aldehydes.
He noted that 316 is more corrosion resistant over all - but especially more resistant to attack by SO2 and SO3. The Mo in the alloy does that trick. Neither handle Cl well, but 316 is slightly better - up to about 400ppm. Apparantly the important thing with Cl is to not let it dry on the steel. The green color is most likely from Chromium being leached from spots where corrosion pits have started (may be microscopic).
He noted that citric washes are good for stainless. It removes a lot of metal oxides and leaves chromium oxide - which is the fundamental protective 'scale' on stainless steel.