In fact, I was thinking of this passage in DeVoto when I asked the question in the first place. In particular, DeVoto quite clearly envisions making pitchers of martinis for your guests; the proportion of vermouth and the choice of gin, then, are fixed for the crowd. He assumes that you have good taste and that your friends will share it. If not, he is quite ready to suggest that they are not really worth knowing. And yet he is quite clear in asserting that you must serve the entire pitcher promptly, and that any remainder should be discarded before mixing a fresh round. "The fragile tie of ectasy is broken in a few minutes." Where else in cooking would we say this? I can think of a few obvious cases: - thermally unstable preparations (souffles; Alinea's truffle explosion) - air-sensitive wines (some very old wines may be drinkable for a few minutes but oxidize almost immediately on being served) - physically-unstable suspensions (emulsions that break, sausages that dry out if held too long; unrested meats) - slow reactions (chopped vs mashed garlic; bruised fruit; oxidized avocado; coriander/anise/licorice conversion) I would have assumed, like slkinsey above, that we're chiefly concerned about protecting volatiles in vermouth. But while fresh vermouth is doubtless better than stale vermouth, people like DeVoto go to great lengths to emphasize that martinis must be FRESH but never tell you to purchase fresh vermouth. Julia Child recommends cooking with vermouth because it remains fresh longer than white wine. Certainly, you can open a bottle of vermouth, enjoy some now, enjoy it again week later, and think nothing of the matter. You probably wouldn't do this to a Chablis. I notice, too, that one of the aromatics associated with vermouth is coriander, and coriander does have tricky decomposition properties -- for example, stale coriander leaves develop licorice aromas. I'd be interested in opinions from people with better palates than mine as to whether a freshly-made martini does taste differently from one mixed, say, an hour previously and held (with *external* ice -- not diluted!).