In the previous Halachot, we have explained the fundamental laws of Kiddush on Shabbat night. Let us now discuss some of the laws of Kiddush on Shabbat morning.
The Gemara (Pesachim 106a) states, “Our Sages taught: ‘Remember the day of Shabbat to sanctify it,’ remember it upon wine at its entrance (at night). How do we know that Kiddush must be recited on Shabbat day as well? The verse states, ‘The day of Shabbat.’” We derive from this Gemara that it is a Mitzvah to recite Kiddush on both the night and day of Shabbat. Nevertheless, on Shabbat morning, we do not recite the “Mekadesh Ha’Shabbat” blessing; rather, we recite only the “Boreh Peri Ha’Gefen” blessing as the Gemara (ibid.) states. The Shabbat morning Kiddush is called the “Grand Kiddush”.
Most Rishonim are of the opinion that the Mitzvah of Kiddush on Shabbat morning is not a Torah obligation and is only rabbinic. When the Gemara states the Mitzvah of Kiddush on Shabbat morning is derived from the verse of “The day of Shabbat”, this is merely a rabbinic law whose source is hinted in the Torah but is not actually a Torah commandment. On the other hand, according to the Maharam of Rottenberg, Kiddush on Shabbat morning is a Torah obligation as it is on Shabbat night. Thus, although the Maharam would customarily fast on Rosh Hashanah, he would nevertheless recite Kiddush on wine, for he maintained that this was a Torah obligation. However, as we have established, the vast majority of Poskim maintain that Kiddush on Shabbat morning is merely a rabbinic enactment.
The Rambam writes that one may not taste any food or beverage before reciting Kiddush on Shabbat morning. This means that one who returns home from the Shabbat morning prayers of Shacharit and Mussaf may not taste anything until one recites Kiddush. Nevertheless, one may have some tea or coffee before morning prayers on Shabbat as one would during the rest of the week since the obligation to recite Kiddush only takes effect after one has prayed.
Although some Poskim disagree with the Rambam on this issue and write that the only prohibition to eat or drink before Kiddush only applies on Shabbat not and not on Shabbat day (which is indeed the opinion of the Ra’avad), nevertheless, we follow the opinion of the Rambam on this matter, for this is indeed the opinion of Maran Ha’Shulchan Aruch as well, whose rulings we have accepted. Only after reciting Kiddush may one partake of cakes, cookies, and the like and drink whatever one wishes or to wash one’s hands and partake of the Shabbat day meal.
Summary: One must recite Kiddush on Shabbat morning. This is a rabbinic enactment and is not a Torah obligation. Once one becomes obligated to recite Kiddush, i.e. after Shacharit and Mussaf prayers, one may not taste any food or beverage until one recites Kiddush. Nevertheless, one may drink either tea, coffee, or water before prayers as one would on any other weekday.