Question: Is it permitted to speak after washing mayim acharonim?
Discussion: The Gemara and Rishonim do not directly address this question. Although the Gemara63 states that Birkas Hamazon must follow immediately after washing, this may only preclude eating between washing and bentching. Talking, on the other hand, might not be considered a hefsek. However, some Acharonim write that talking is also forbidden.64
Mishnah Berurah65 rules that lechatchilah, one should not speak after washing, even if he wishes to speak about divrei Torah.66 If an important matter arises, though, it is permitted to speak.67 Therefore, if one plans to say pesukim before bentching, such as Al Naharos Bavel or Shir Hama’alos, he should do so before washing mayim acharonim.68 However, if a need arises to go to the bathroom, one may recite the berachah of Asher Yatzar after washing mayim acharonim.69 Similarly, someone who sees lightning or hears thunder after mayim acharonim may also recite the appropriate berachos.70
Question: If a person spoke between mayim acharonim and bentching, is there a reason for him to wash a second time?
Discussion: Since it is appropriate for mayim acharonim to be immediately before bentching, it would seem that someone who spoke should wash again so that the washing is performed before bentching without any interruption. However, it can be argued that once a person has already cleaned his hands from any residue of food or salt, washing again is meaningless and does reconnect mayim acharonim with Birkas Hamazon.71
Many Poskim72 rule that one should indeed wash a second time. This is because, aside from the halachic reasons for mayim acharonim, there are also reasons based on Kabbalah that apply even if a person’s hands are clean. Therefore, one should wash again because that washing will fulfill the kabbalistic reasons for mayim acharonim and be performed immediately before bentching.73 Some suggest that a person should deliberately make his hands dirty, such as by scratching his head. This will create an obligation to wash again, even according to basic halachic reasons for mayim acharonim.74
The above ruling that one should rewash after speaking is applicable regardless of whether speaking was permitted (e.g., he had to recite Asher Yatzar) or forbidden.
Question: How much water is necessary for mayim acharonim?
Discussion: According to the basic halachah, any amount of water is sufficient for mayim acharonim, provided that it is enough to wash until the second segment of the fingers, and the first segment of the thumb.75
However, it is recorded that the practice of the Vilna Gaon was to use a revi’is of water for mayim acharonim.76 Later Poskim, though, debate the veracity of this recording.77
On the other hand, according to the teachings of Kabbalah, a person should use a minimal amount of water for mayim acharonim. In a situation where a person’s hands are very dirty, he should wash them with the intention of eating more afterward. This initial washing will not be considered mayim acharonim since he is not finished eating. Afterward, he should eat a piece of bread and then wash mayim acharonim using a minimal amount of water.78
63 Berachos 42a, according to the explanation of Rashi, s.v. Lenetilas.
64 Beis Yosef 179, ד"ה ויש infers this ruling from Rosh’s practice cited in Tur 166; Magen Avraham 179:1. However, Kesef Mishneh, Berachos 6:20, maintains that both Rashi and Rambam allow speaking after mayim acharonim. Aruch Hashulchan 181:1 concurs with this opinion, but in 181:9 writes that it is best to refrain from speaking after mayim acharonim.
65 179:1. In his view, one should not speak even one word (165, note 7, with Sha’ar Hatziyun 13). However, see Shulchan Aruch Harav 181:6 who rules that speaking “two or three words” is permitted.
66 Mishnah Berurah 181:24.
67 Mishnah Berurah 179:1.
68 Aruch Hashulchan 181:9.
69 Eishel Avraham (Buczacz), Tinyana, 181:6 (Machon Yerushalayim ed.).
70 Eishel Avraham (Buczacz), 179:1.
71 Mishnah Berurah seems to offer contradictory rulings on this question. See 179:1 and Sha’ar Hatziyun 179:7. For a possible resolution to this contradiction, see Chiddushei Basra 179.
72 Mishnah Berurah ibid.; Eishel Avraham (Buczacz), 179:1 and 181:6; R’ C. Kanievsky cited in Vezos Haberachah 14, p. 139.
73 Eishel Avraham 181:6.
74 Eishel Avraham (Buczacz), 179:1.
75 Beis Yosef cited in Mishnah Berurah 181:19.
76 Ma’aseh Rav 84. See Teshuvos Vehanhagos I:173, who explains that this view maintains that mayim acharonim is similar to netilas yadayim, where a revi’is is required. [Some understand that according to the Vilna Gaon, one must also wash until the wrist; see Teshuvos Vehanhagos ibid. Others understand even according to the Vilna Gaon, it is sufficient to wash until the knuckles; see Beiur Halachah 181:4 and Hilchos Yom Beyom II:2, footnote 27.] Similarly, according to this opinion, the water should be poured using koach gavra – human force; see Hilchos Yom Beyom (II, 2:22). The primary halachah, though, does not follow this view; see Mishnah Berurah 181, notes 19 and 21.
77 See Orchos Rabbeinu (p. 162) who cites R’ Y. Y. Kanievsky quoting the Chazon Ish, stating that this recording is unreliable. However, it is cited in Mishnah Berurah 181:19. See also Teshuvos Vehanhagos (ibid.), who writes that it is well known that this was the practice of the Vilna Gaon and is adhered to by all his students.
78 Ben Ish Chai cited in Kaf Hachaim 181:6.