The Appropriate Time for Birkas Hamazon
After finishing the meal, a person should bentch as soon as possible.120 If he did not bentch right away, he may bentch until the food he ate is digested. Shulchan Aruch121 states that digestion occurs when a person begins to feel hungry and is no longer fully satiated from the meal. This point is well before full digestion, which takes at least six hours.122
The Poskim raise two issues with this ruling. 1) It is difficult for the average person to determine whether he has reached the point of “beginning to feel hungry” to ascertain that digestion has begun.123 2) If a person only ate a small amount, how can he determine when digestion begins, given that he felt hungry immediately after eating and would have continued eating if more food were available?124
As a solution to these issues, the Poskim125 cite an opinion126 in the Gemara127 that rules that if a person eats a small meal, he can be certain that digestion has not begun until seventy-two minutes128 have passed from the end of the meal. In their opinion, this view is incorporated into halachah.129 Accordingly, a person who has not eaten his fill or is unsure if digestion has begun can definitely bentch within seventy-two minutes from the end of the meal. With this in mind, the Poskim provide the following guidelines for the timeframe of bentching.
Lechatchilah, a person should bentch when he finishes his meal130 and certainly within seventy-two minutes from the completion of his meal. By adhering to this deadline, one avoids any uncertainties.131 Some Acharonim, however, maintain that even within this timeframe, a person who has not eaten his fill will have a safeik regarding whether he is obligated to bentch.132 To satisfy this opinion, one should eat an additional kezayis of bread before bentching. However, if he does not have any more bread available, he should still bentch, as per the former opinion, since seventy-two minutes have not yet passed.133
After seventy-two minutes have passed from the completion of the meal, one should bentch if he still feels full from the meal.134 But if he no longer feels full, he forfeits his opportunity to bentch.135
If, after seventy-two minutes have elapsed, a person is unsure if he is still full, it would depend on how much he ate at the meal. If he ate until he was satiated, his obligation to bentch is Biblical, and therefore, he must recite Birkas Hamazon out of doubt, following the rule of סָפֵק דְּאוֹרַיְיתָא לְחוּמְרָא – a doubt concerning Biblical law is treated stringently. However, if he did not eat until he was satiated, he does not bentch out of doubt, since one who did not eat until the point of satiation is only obligated to bentch by rabbinic decree,136 so the general rule of not saying berachos when in doubt applies. Nevertheless, in this case, it is appropriate for a yerei shamayim to wash his hands, recite Homotzi, and eat another kezayis of bread. This allows him to bentch and thus resolve any doubt.137
If a person still feels full only because he ate other foods after eating the bread, it depends on the following: If those foods were not eaten at the same meal as the bread, he can only bentch if he is still full from the bread itself. However, if they were eaten during the same meal as the bread, then it is as if his bread meal continued, and he can bentch even if there was a significant break between eating the bread itself and bentching.138
120 Aruch Hashulchan 184:1; Sha’ar Hatziyun 606:2. This also seems to be implied by Mishnah Berurah 184, note 16.
121 184:5.
122 Magen Avraham 184:9.
123 Aruch Hashulchan 184:7.
124 Taz 184:2; Magen Avraham ibid.
125 Taz ibid; Avudraham cited in Darkei Moshe 184:1.
126 This is the opinion of Reish Lakish as explained by Tosafos, s.v. Be’achilah.
127 Berachos 53b.
128 The Gemara says that the time is the equivalent it takes to walk four mil. It takes eighteen minutes to walk a mil and seventy-two minutes to walk four mil (Mishnah Berurah 184:20).
129 See Beiur Halachah 184:5, ד"ה אם for an elaboration on this opinion. However, see Magen Avraham 184:9, who maintains that this opinion is not incorporated into the final halachah.
130 See footnote 25.
131 Based on Aruch Hashulchan 184:7-8; Kovetz Teshuvos 1:21.
132 Mishnah Berurah 184, note 20, citing the opinion of Magen Avraham. See above, footnote 33.
133 Mishnah Berurah 184, note 20.
134 See however Kaf Hachaim (184:28) who maintains that one who delays bentching until after seventy-two minutes should eat an additional kezayis even if he still feels full from his meal. This is also the opinion of Rav Y.S. Elyashiv, cited in Vezos Haberachah 5, p. 49.
135 Shulchan Aruch 184:5.
136 Likewise, someone who has this uncertainty after consuming foods whose berachah acharonah is only of rabbinic origin, such as after eating fruits or vegetables, should not recite the berachah acharonah out of doubt; see Shulchan Aruch 209:3. However, see Mishnah Berurah 209, note 10, regarding the berachah acharonah recited after eating the Shivas Haminim.
137 See Shulchan Aruch 184:4 and Mishnah Berurah, note 15; Shulchan Aruch 209:3; Vezos Haberachah 5, p. 49, based on Aruch Hashulchan 184:8. See also Vezos Haberachah ibid., where he writes that even someone who ate until he was satisfied should eat another kezayis of bread to create a definite obligation.
138 Mishnah Berurah 184:18. Kaf Hachaim 184:31, however, writes that in the latter case, lechatchilah, one should eat another kezayis of bread before bentching.