Does opening a new bottle create a new Keli, such that it would be prohibited on Shabbath?
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The possible problem with opening bottles and cans is, by creating a new vessel (kli), one would be performing the melachos (creative actions) of boneh (building) and makeh b'patish (striking the final hammer blow / completing a creative act)
There is a difference between opening bottles and cans on shabbos.
A bottle is made as a complete vessel. The cap on both plastic and glass bottles is manufactured separately from the bottle itself, and then affixed to the top of the bottle after the bottle has been filled with liquid. Removing the cap from this kind of container is not making a new vessel, because the bottle itself was already fully made beforehand.
Contrast this with an aluminum soda can. Since the tab of the can is part of the top seal itself, the can has never been a functioning vessel (i.e. one that can be accessed to fill and empty).
By pressing in the tab of the aluminum soda can, one actually completes the "manufacture" of a new vessel. This is forbidden on shabbos for the reasons stated above.
Watch soda cans being made here: http://www.youtube.com/watch?v=CPFzr50TkP0
When it comes to other metal cans, such as canned tuna, beans, etc. a similar problem exists. The can itself is completely sealed, and opening it would create a new vessel.
(This is only permissible if one does not want to keep the can. If one has a desire to reuse the can, even with a hole, the problem of creating a usable vessel still applies).
It is unclear to me if this method would also remove the problem of opening a soda can on shabbos - because the pushing in of the tab is still a positive / creative act. I suppose one could access the soda by cutting off the back end of the can, but that would be very messy, especially when dealing with a carbonated beverage.
HaRav Mutzafi (Question 91,196 on Doresh-Tzion.co.il) says