If one simply observes the ways that people conduct themselves in the matter of Kiddush on Shabbos morning, there could be some confusion as to what is the proper manner for Kiddush. 

In following the guidelines established in the Shulchan Aruch (Orach Chaim, 272) the most preferred beverage is wine in a cup that contains a required “shiur” of a “reviis” (displacement of an egg and a half.)  The one making the Kiddush must drink a “rov” or the majority of the wine in the cup.  For further details concerning the drinking or distribution of the Kiddush wine one should refer to the Shulchan Aruch (ibid.)  However, one cannot help notice that there are many individuals who, when they are joining in any Kiddush procedure, will use a small glass with whiskey for this purpose.  This seems to contradict the above-mentioned sources quoted regarding the use of wine and in a required shiur. 

Even when one wants to use some other beverage, which is accepted as “Chamar d’medina” or popular drink used by most people, it still seems necessary to have the proper shiur (ibid, Mishna Brura).  What then is the basis of using the small “shot” glass of whiskey for Kiddush on Shabbos morning?   

This matter is discussed by the eminent posek Maharsham in his responsa (Sheila v’Tshuvos Maharsham Vol. I, 175).  He cites the minhag of several Chasidic geonim who recited Kiddush on the small glass of liquor on Shabbos morning when the entire law of Kiddush is “midarabonon”, a rabbinic obligation (rather than ordained by Torah law).