Halachos of the Cup
38. One must make sure that the Kiddush cup satisfies the requirements of a kos shel brachah (המבוארים באו''ח סי' קפ''ג ס''ב) (see issue 368 at length)
39. Full. Thus, lechatchilah one must make Kiddush on a cup that is filled (שו''ע רע''א ס''י) to the brim (רמ''א קפ''ג ס''ב). If the empty space is noticeable, it is better to pour the wine into a smaller cup, assuming it contains a revi’is. One can also put an ice cube into the cup to make it full (ע''פ מ''ב סי' קפ''ב סקל''ב).
40. As long as there was a revi’is, it is okay bedieved even if the cup was not full (מ"ב סקמ''ב). A revi’is is 150 – gematria כוס הגון – cc [Chazon Ish] or 86 – gematria כוס – cc [Rav Chaim Naeh]. For Friday night Kiddush, which is deoraisa, one should be machmir for the bigger shiur (מ''ב סקס''ח).
41. Even when there is only a revi’is, lechatchilah one does not need to drink more than a cheekful, which for most people is 50-55 cc ( 'ס מדות ושיעורי תורה פט"ז אות י"א) within the amount of time it takes to drink a revi’is (מ''ב שם).
42. Not “pagum.” One must also make sure that the cup is not pagum, i.e., that no one drank even a drop (מ''ב קפ''ב ס''ג) from it (שו"ע רע"א ס"י). Bedieved if there is no way to fix it, one may make Kiddush with it (קפ''ג ס "ז). Some prefer making Kiddush on challos than on a cup that is pagum, at least on Friday night (מ"ב סקמ''ג בשם הפמ''ג )(see 369, para. 13).
43. If one wants to make Kiddush with a cup that someone else made Kiddush with and drank from, he must fix it before making Kiddush. This can be done by pouring a bit of wine into the cup, then pouring all the wine back into the bottle [this is not called reuse of the bottle that would obligate toiveling it as long as there is still wine in the bottle]. He can also rinse the cup inside and out and then fill it again (see issue 93, para 8).
44. Whole cup. Lechatchilah one must also make sure that the cup is whole (מ"ב סקמ''ד), i.e., the cup itself should not be broken, punctured, damaged even slightly on the rim, or cracked even without anything missing. One should make sure that not even the base is broken (מ''ב קפ''ג סקי''א). Nevertheless, bedieved it is muttar (מ''ב שם סק''י).
45. If there is a hole in the bottom or side of the cup and it cannot hold a revi’is, it is unfit even bedieved. If one made Kiddush with it, it is like he didn’t make Kiddush (שע ה"צ קפג סקי"ד). However, if there was a bottle of wine with a revi’is in front of the person when he made Kiddush, the Kiddush took effect on the wine in the bottle (הגר''ש וואזנר, קובץ מבית לוי ח''ג עמ' ע ').
46. Rinsing the cup. The cup must be well-rinsed inside and out (מ''ב סקמ''ד). One can wipe it with a cloth (מ''ב קפ''ג סק''א), but according to the Zohar, it is better to rinse it with water (כ פה"ח שם סק''ד). If it is clean, e.g., it was rinsed after the previous Shabbos, strictly speaking it does not need to be rinsed again (שו''ע קפ''ג ס''א, חוט שני שבת ח''ד פפ''ה סקי''ד). However, some are always careful to rinse it with water, even if it is clean (כ פה"ח שם).
Disposable Cup
47. Lechatchilah one should not use a disposable cup for Kiddush since it does not have the substantiality of a real cup. However, if one has no other cup, he may be meikel (שו"ת אג''מ או''ח ח''ג סי' ל''ט, שו''ת מנח''י ח''י סי' כ''ג).
48. Some people think that using two disposable cups together is better. This is no better; adding a cup does not add substantiality.
