Some forbid opening a pop-top can on Shabbat. They are concerned that this action may constitute Boneh, because it creates a neat opening that allows one to drink. They are also concerned that one may be transgressing Meĥatekh, because the tab is pre-scored and produces a very precise opening.
However, many permit this, maintaining that because the can is meant to be disposable, opening the top does not create a receptacle. Rather, it is comparable to breaking a barrel in order to remove the wine inside it. Meĥatekh is also not an issue, because that applies only when material must be cut to an exact size. Since it does not matter where a cut is made on the can, and the only goal is to create an opening for drinking, the can may be opened in the most convenient way possible – by lifting the tab.
One may be lenient if he wishes. If one wishes to be stringent, he should not drink from the opening formed by popping the top, but rather should pour the drink from the can into his cup. This makes it clear that he is not interested in the neat opening of the can. If one wishes to be more stringent, he should be careful to lift the tab only slightly, less than he would on a weekday. This way the act of cutting is not completed, and the opening is not as good as it is usually.
There is another case that is subject to debate. Many dairy products (yogurts, puddings, and the like) come in containers that are loosely connected to each other. May one separate them by applying light pressure to that connection?
Some maintain that breaking the containers apart along score lines that are made for this purpose is a violation of the Torah prohibition of Meĥatekh. They are also concerned that this might be Makeh Be-fatish, since separating the containers makes them usable.
Others are lenient, maintaining that cutting is forbidden only when it is precise, and here the goal is simply to separate the containers from one another. No one cares exactly how precise the cut is. Furthermore, it is not Makeh Be-fatish, since the containers were completely ready for use even beforehand. Separating them simply removes an external impediment.
In practice, one who wishes to be lenient has an opinion to rely upon, and one who chooses to be stringent should be commended. It is proper to separate such containers before Shabbat.
. Orĥot Shabbat 11:43 and 12:5 cite R. Yosef Shalom Elyashiv as forbidding opening a pop-top can in the normal manner and R. Shlomo Zalman Auerbach as permitting this. R. Meir Mazuz and Menuĥat Ahava 3:24:5 permit this on condition that one pours the drink into the cup. This approach is also recorded in Eshmera Shabbat 1:1:17. Or Le-Tziyon 2:27:6 permits this on condition that the pop top is not opened entirely, so that the can will not be easily usable. Accordingly, even those who are stringent would concede that a complete melakha was not performed. Yalkut Yosef 314:23 states in the name of R. Ovadia Yosef that technically one may open a pop top, but it is proper to be stringent and not open it entirely.
. Included among the permissive poskim are: R. Shlomo Zalman Auerbach (Shulĥan Shlomo 314:13:3); Or Le-Tziyon 2:27, n. 7; Halikhot Olam vol. 4, p. 254; and Binyan Shabbat 11:3. Included among the stringent poskim are: R. Yosef Shalom Elyashiv (quoted in Orĥot Shabbat ch. 12 n. 22); Ĥut Shani vol. 1, pp. 128-129; R. Mordechai Eliyahu; and Menuĥat Ahava 3:16:14. Even though some state that this is a Torah prohibition, it seems that Rambam (MT Laws of Yom Tov 4:8) maintains that if there is a prohibition at all, it is only rabbinic. Therefore, I wrote in the main text that one who wishes to be lenient has an opinion to rely upon.
There is a debate about tearing open small sugar packets that are often perforated to facilitate tearing them. According to R. Shlomo Zalman Auerbach, one may tear along the dotted lines, because no one cares exactly where the cut is; the point of the perforation is to make it easier to tear open. R. Yosef Shalom Elyashiv, however, maintains that the prohibition of Meĥatekh applies because one is cutting precisely. Therefore, the packet must be torn at a different place (Orĥot Shabbat 11:41).