Unicum. Unicum is a Hungarian herbal bitters, drunk as a digestif and aperitif. Apéritif unicum is an herbal digestif. Liqueur the liqueur is today produced By zwack according to a secret formula of more than forty, herbs and the drink is aged in oak. casksnicum. Unicum is a Hungarian herbal bitters, drunk as a digestif and aperitif. Apéritif unicum is an herbal digestif. Liqueur the liqueur is today produced By zwack according to a secret formula of more than forty, herbs and the drink is aged in oak. casks