The Gemara of Shabat establishes the prohibition against creating a keli (functional utensil) on Shabat. Concerning a bottle, the bottle itself already has the status of a keli before one removes the cap, but the cap perhaps becomes a keli as a result of its removal. Even though the cap already serves as a utensil in that it covers the bottle, breaking the ring that attaches the cap to the bottle enables one to use this cap to cover a different bottle, and it would thus seem that removing the cap transgresses the prohibition of creating a keli on Shabat.
Ha’Rav Ovadyah Yosef (a”h), however, rules that it is permissible to open a new bottle on Shabat, because people generally do not use the cap from one bottle to cover a different bottle. Therefore, since the cap already functions as a keli with respect to the original bottle, one does not create a keli by removing it. It would be forbidden to remove the cap for the purpose of using it to cover a different bottle. This is the position as well of Rabbi Moshe Halevi, in his sefer “Menuchat Ahavah.”
Other Rabanim however, rule stringently on this issue, claiming that removing a bottle cap transforms it into a keli even with respect to the original bottle. Rabbi Moshe Halevi therefore recommends opening one’s wine bottles before Shabat. With regard to carbonated drinks, however, one may certainly rely on the lenient view and open them on Shabat.
