According to Nora's own words in Act III of A Doll's House, during the party Torvald enjoyed tremendously the excellent champagne that was given to them. As a result, Nora explains to Dr. Rank
Torvald drank a great deal of champagne to-night tooand he is always in such good spirits afterwards.
As with any type of alcoholic beverage, which are natural depressants, Torvald's mood changes to calm, mellow, and flirtatious toward his wife. This is an irony because, shortly thereafter, there will be the ultimate clash between Nora and Torvald which will result in the unthinkable act of Nora leaving the family home forever. Hence, it is arguable that Ibsen used the champagne as a catalyst that will make the scene all the more dynamic when Torvald goes from mellow, loving husband to a name-calling, senseless, and mean man after learning Nora's truth. Granted, it is NOT the champagne what switches Torvald's mood after learning the truth; it is the fact that he has taken Nora for granted for so long that this mistake on her part, in his eyes, cannot be forgiven. Of course, after Nora threatens to leave and is serious about it Torvald changes yet again and eases his attitude. But it is too late now; Nora has finally grown up.