One who is a Rebbi in a Yeshiva and needs to make Kiddush for the Bachurim but the only bottle of grape juice is closed, should he hint to the Bachurim to open it, or simply sit there until someone will open it? To make Kiddush on the challas will be extremely strange, as the grape juice and Becher (cup) were already on the Rebbi’s table and the Bachurim are expecting to hear Kiddush in the traditional way.

When opening the common grape juice bottles of our days, one may be turning the cap into a usable utensil, since after the ring that attaches it to the bottle is broken and separated from the cap, it can be reused many times and should be considered as having created a new ‘Keli” or utensil which is prohibited on Shabbos. Therefore, Horav Shlomo Miller’s Shlit’a opinion is that the best way to open the bottle of juice is by first making a hole with a pointed knife on the cap of the bottle, (carefully avoiding to destroy or obliterate any letters), thus destroying its value as a utensil. (see also Shmiras Shabbos K. 9: 61). After, having done that you may be stringent and have two people open the bottle with a ‘Shinui’ or a different way of doing it normally. One may just hold on to the cap firmly without turning it, while another would turn the bottle itself and thus detach it from the cap. On small bottles, when the bottle will be emptied immediately after opening, many Poskim permit. (see sources above).