The Sages ordained that a number of berakhot be recited over a kos (goblet) of wine, such as the berakha over betrothal, marriage, Birkat Ha-mazon (Grace after Meals), kiddush, and havdala. Since these berakhot are made over a kos to glorify God, it is proper that the kos be pretty and elegant. The Sages established the following rules about it.
The kos must be whole, without defects or breaks on the rim or the base. If the kos is not whole, but no other kos is available, one may still use it be-di’avad. However, if it is cracked to the point that the wine leaks out, leaving less than a revi’it, it may not be used.
If there are several available cups, one should pick out the nicest one to use for the berakha. Many use a silver goblet for kiddush. If the only kos available is a plastic disposable one, it may be used be-di’avad.
The kos must be totally clean. If it was drunk from or otherwise got dirty, it must be washed inside and out (SA 183:1). Be-di’avad, if it is difficult to wash the kos, one may wipe it out and clean it using a napkin (MB ad loc. 1).
Although a kos that holds a revi’it is sufficient, if a larger cup is used, there is a mitzva to fill it up all the way since it is more dignified for the berakha to be made over a full cup. Some are accustomed to fill the kos to overflowing, to the point that whoever is making kiddush will probably spill wine on his hand. It would seem preferable to fill the kos close to the top but not to overflowing, so that the wine does not spill. This is what the Sages meant when they spoke of a full kos (Taz 183:4; SAH 4; MB 183:9; proof of this is the explanation given of Beit Hillel’s opinion in Berakhot 52b).
If one drank from the wine while it was in the kos or directly from the wine bottle, the wine remaining in the kos or bottle is called pagum (defective) and considered unfit for sacramental purposes. When necessary, one can fix pagum wine by adding non-defective wine to it. Once the additional wine is added, all the wine is considered new. If the wine is strong, one can fix it by adding water instead. Be-di’avad, if there is no way to fix the wine, one may make kiddush on pagum wine (SA 182:3-7).
The Sages stated that one should first take the kos in both hands in order to show how dear it is. Then, when making kiddush, one should hold the kos in the right hand, which is the more important one. He should hold the kos with all his fingers so that they cradle the cup. He should lift the kos a tefaĥ above the table, so that it is visible to all. He should look at the kos so that he is not distracted. If he needs to, he should look in a prayer book, but it is best to place it adjacent to the kos so that he sees both. After he drinks from the wine he should give some to his wife so that the blessing spreads to both of them (SA 183:4).
. “There are ten things said about a kos shel berakha: it must be rinsed and washed, undiluted and full; it requires crowning and wrapping; it must be taken up with both hands and placed in the right hand; it must be raised a tefaĥ from the surface; and he lays his eyes upon it. Some add that he must send it around to the members of his household (i.e., his wife). R. Yoĥanan said: ‘We only know of four: rinsing, washing, undiluted, and full’” (Berakhot 51a). Rambam quotes only the four rules mentioned by R. Yoĥanan. However, this is problematic since R. Yoĥanan himself raises the question as to whether the left hand can assist the right, which evidently means that he considers it a relevant issue as well, even though it is not one of the four things explicitly attributed to him. The Ge’onim record all ten criteria as law, while Rosh leaves out only crowning and wrapping. Talmidei Rabbeinu Yona record five as binding – the first four in the list, plus taking the kos in the right hand. The rest are not obligatory. The Vilna Ga’on explains that the four things mentioned by R. Yoĥanan are mandatory while the rest of the list are a non-obligatory mitzva (183:7). This is also the ruling of MB 183:20. Therefore, if one holds the cup in his left hand, he fulfills his obligation. It would seem that be-di’avad, even if he does not hold the cup at all, but simply has it in front of him while he makes kiddush, he fulfills his obligation (MB 182:15). There are varying customs for left-handed individuals. The mainstream poskim maintain that he should take the cup in his left hand, which is his stronger hand (MB 183:20). However, according to Kabbala, he should use his right hand; many follow this opinion (Kaf Ha-ĥayim 183:29, Piskei Teshuvot 183:10).
There is further debate about the ideal way to hold the cup. Shlah, quoted by MB 183:15, states that based on Kabbala one should rest the cup in the palm of the right hand, with the fingers standing erect around the cup. Kaf Ha-ĥayim states that he should first straighten his fingers and then place the cup at the middle of their length. MA 183:6 states that it is possible to understand the kabbalists as saying that one should place his fingers around the cup the way he normally does. See Peninei Halakha: Berakhot ch. 5 n. 22 and Harĥavot here.