I did a little Googling (and admit it’s something I should’ve done in the first place) but I found that the pepper trick is from Moonraker. It’s summarized on Moonraker page in the Make Mine a 007 site as follows:

When the vodka arrives in a frosted carafe, M pours three fingers of the liquor for 007. Bond then takes a pinch of pepper and drops it in the vodka. Most of it settles to the bottom, but 007 uses his fingertip to dab up the remaining grains on the surface, and then knocks back the vodka. M gives him a look of �ironical inquiry.� Bond explains it�s a trick he learned while he was attached to the embassy in Moscow. The dash of pepper sends poisonous fusel oil from badly distilled vodka to the bottom of the glass. He adds that he got to like the taste, �But I shouldn�t have insulted the club Wolfschmidt.� M remarks, �So long as you don�t put pepper in Basildon�s favourite champagne.�