If Mr. Rea and others give “Mad Men” high marks for nailing its milieu, part of the credit for this achievement goes to Ms. Perello, 43, who prepares every drink seen on the show, using nonalcoholic ingredients. “We’re definitely the alcohol department,” she said. “I can make an old-fashioned in my sleep now.”

To get an idea of the popular cocktails of the time and how they looked, Ms. Perello relies heavily on a volume from 1992 called “The Art of the Cocktail: 100 Classic Cocktail Recipes,” by Philip Collins. Little is left to chance. “We’re very picky about our glassware. Things are bit bigger and bulkier now. For a martini glass, we go a little smaller and thinner.” Period bottle labels and caps (old-style tax stamps, yes; bar codes, no) are recreated by the graphics department, using old ads as guides.

Occasionally, expediency dictates a decision. When an accounts executive was sent a case of gin by some British colleagues last season, Ms. Perello chose Tanqueray, though Beefeater then dominated the London dry gin market in the United States. “Tanqueray has not changed their bottle,” she explained. “With Beefeater, the bottles are completely different than they were. And I needed 12 bottles.”

Liquor is not only an integral part of many plotlines (last season, it played a pivotal role in a car crash, a divorce, a rape and two career implosions), but often a telling sign of character. When it comes to choosing a character’s poison, Ms. Perello said, many people have input, starting with the show’s creator, Matthew Weiner: “Matt will say, ‘I want them to have a brown liquor.’ And I’ll go, ‘Let’s do a nonblended Scotch, because this is a person who would appreciate that.’ ”

The cocktail historian David Wondrich, 48, thinks an old-fashioned is a conservative choice for the young Draper, but considers his preference for Canadian Club “exactly right. We’d had years of destruction of the American whiskey industry up until then. So the Canadian stuff was viewed as being pretty good.”

“The big Scotches were Bell’s, Black & White, Teacher’s, White Horse,” Mr. Rea said. “When you’re drinking Canadian Club, you’re showing people you drink a better brand” of whiskey. He and Mr. Wondrich also said Betty Draper’s taste for Tom Collinses and vodka gimlets was spot on.

Thirsts on “Mad Men” have not slackened in Season 3. Draper will vary his rye intake with Old Overholt, while Roger Sterling, Draper’s boss and the show’s resident booze philosopher, broadens his palate. About Sterling’s beloved vodka (bottles of Smirnoff made frequent cameos in earlier episodes) Mr. Rea said, “Martinis were the big thing in those days. Vodka was just beginning to come on strong.”

This season, Sterling gets his hands on some prized contraband: Soviet-made Stolichnaya (then not available in the United States). His priorities remain solidly in place. “Help yourself,” he tells a colleague. “Not the Stoli.”