Waiting six hours between eating meat and milk:
It is a Rabbinical obligation to separate one’s meat and dairy meals from each other. It is disputed amongst Poskim as to how the two meals are to be separated. Some Poskim rule one is Rabbinically required to wait six hours between eating meat and then dairy [and so is the ruling of Sephardic Jewry]. Other Poskim however rule one is not required to wait any time between eating meat and then dairy, and rather is to simply clean and wash his mouth and hands, and recite Birchas Hamazon, and he may then eat dairy. Based on this, the Ashkenazi custom [in previous times] was to wait [only] one hour between meat and dairy. Nevertheless, the meticulous [even amongst Ashkenazi Jewry] were particular to wait six hours between eating meat and dairy and so is the proper custom. Practically, today, every person who has a spirit of Torah is to wait six hours [and so is the widespread custom today amongst all Jewry, with exception to Ashkenazim of certain European regions, such as the Deutsch, who only wait three hours]. One who does not wait six hours is to be protested, especially if he is a Ben Torah. One who does not wait six hours is considered a Poretz Geder, in all its severity.
Q&A on from when to wait 6 hours
From when does one begin to count the six hours-from the time he finished eating the meat or from after saying the after blessing for the meal?
The six hours is counted starting from the time he finished eating the meat, even if the meal itself concluded at a much later time. However, some Poskim rule one is to wait six hours from the end of the meal, from when the after blessing was said and onwards, even if he finished eating the meat much time earlier. Practically, the custom is like the first opinion.
May one begin eating a dairy meal within the 6 hours, if he will abstain from eating actual dairy products until 6 hours have passed?
If one is eating a very long meal [i.e. wedding feast, all-nighter Farbrengen] and six hours have passed since last eating meat, may he now eat dairy during this meal prior to reciting Birchas Hamazon?
No. One must always say an after blessing for the meat prior to eating milk products even if 6 hours have already passed from the time that he ate the meat. This applies even if he did not eat bread in the meat meal. [If, however, too much time has passed, and he is no longer Halachically able to say the after blessing, then he is to eat dairy without saying it so long as he has removed himself from the meat meal.]
Q&A on calculating the 6 hours
Must one wait 6 full hours, or does it suffice to wait “into” the 6th hour, which is after 5 hours have passed?
One must wait six full hours. However, there are Poskim who permit waiting into the start of the 6th hour which is as soon as five hours have passed. The final ruling and custom is like the former opinion.
Are the six hours calculated as 60 minutes each or as Zmaniyos hours?
The hours are not Zmaniyos and contain 60 minutes each during all times of the year.
Must one wait six hours between meat and dairy even in the winter months?
Yes. One is required to wait six hours both in winter and summer. However, some Poskim are lenient to allow waiting 4 hours in the winter. We do not rule like this opinion.
If one slept after eating meat may he wait less than six hours prior to eating dairy?
No. However, there are Poskim who are lenient and allow waiting 1-2 hours less.
If one is unsure how much time has passed since he ate meat, what is he to do?
Some Poskim rule that if one is in doubt as to whether six hours have passed then he must wait until he is certain the time has passed. Other Poskim, however, rule that one may be lenient. Practically one who chooses to be lenient has upon whom to rely.
 Rav Chisda in Chulin 105a
 Michaber 89/1; Rambam Machalos Assuros 9/28; Ran Chulin 37b that so is opinion of Rif; Rabbeinu Chananel; Baal Haitur 2/13Tur O.C. 173 in name of Rosh; Tur Y.D. 89; Rosh Chulin 5 that so is custom; Shut Min Hashamayim 55 that so is opinion of majority of Poskim, and in Heaven there is no dispute in this, as everyone now agrees its forbidden; Taz 89/2 in name of Shaareiy Dura that custom is like Rambam and not like Tosfos; Rashal Kol Habasar 70 wonders why Ashkenazi Jewry became accustomed to be lenient against the Rambam and Rif
Custom of Arizal and father of Mar Ukva: The father of Mar Ukva would not eat dairy until the next day. [Chulin ibid]The Arizal was accustomed to wait until the night [next Halachic day] until he would eat meat/dairy. [Shaar Hamitzvos Parshas Mishpatim; Kaf Hachaim 89/10]
 Opinion in Rama ibid; Tosfos Chulin 104b and 105a [however does not mention the need to clean mouth and hands]; Ravaya; Bahag Brachos 6/9; Rosh Chulin 5 in name of Rabbeinu Tam
 The reason: The basis of this dispute is in the words of the Talmud which requires one to wait from meal to meal between eating meat and milk. The first opinion rules “from meal to meal” refers to from the morning meal to the evening meal, which is 6 hours. The second opinion rules it simply refers to two different meals separated by an after blessing. [Shach 89/5]
 So was the custom in Holland. In many other European countries, the custom was to wait three hours between meat and milk.
 Rama ibid
The reason: This hour wait is not required from the letter of the law according to any Posek, as it does not suffice for the first opinion who requires a six hour wait and is not required by the second opinion. Nonetheless, it became widespread as a form of compromise between the two opinions. [Taz 89/2 in name of Mahariy]
 Rama ibid
 Shach 89/8 in name of Rashal; Taz 89/2 in name of Terumos Hadeshen and Shaareiy Dura; Rashal Kol Habasar 70 wonders why Ashkenazi Jewry became accustomed to be lenient against the Rambam and Rif
 P”M 89 S.D. 5 and 8; Chochmas Adam 40/13; Aruch Hashulchan 89/7; Kaf Hachaim 89/20; See Shut Min Hashamayim 55 in Heaven there is no dispute in this, as everyone now agrees one must wait six hours
 Taz ibid in name of Shaarei Dura
 Aruch Hashulchan ibid
 Rama 89:1:” It does not make a difference if one waits the hour before or after he bentches”; Degul Merivava on Shach 89:3; Darkei Teshuvah 89:4; Kaf Hachaim 89:9
 Aruch Hashulchan 89:4
 The reason: As the Gemara ibid emphasizes a wait between meals, and hence so long as the meal has not concluded, the six hours cannot begin. [Aruch Hashulchan ibid]
 Hakashrus 10 footnote 69 based on Poskim ibid that we follow the end of eating the actual meat
 Aruch Hashulchan 89:4; See also wording in Degul Mirivava ibid “From the end of eating the meat until the start of the dairy meal”
 The reason: As the Gemara ibid emphasizes a wait between meals, and hence so long as the six hours have not concluded a meal in which one eats dairy may not be eaten. [Aruch Hashulchan ibid]
 Shach 87:5; Rashal, brought in Shach 89:5, “Many people are lenient in this and it is a mistake in their hands”; Rashal Kol Habasar 9; Kneses Hagedola 89:3; Peri Chadash 89:5; Beis Lechem Yehuda 89:3; ; Halacha Pesuka 89:1; P”M 89 S.D. 5; Birkeiy Yosef Shiyurei Bracha 89:9; Erech Hashulchan 89:3; Chochmas Adam 40:13; Beis Yitzchak 89:8; Mikdash Me’at 89:5; Kaf Hachaim 89:15
 Shach 89:6; Peri Chadash 89:3; Lechem Hapanim 89:6; Beis Lechem Yehuda 89:4; Kreisi 89:5; P”M 89 S.D. 6; Chochmas Adam 40:13; Beis Yitzchak 89:9; Zivcheiy Tzedek 89:10; Kaf Hachaim 89:23
 One may not recite any after blessing [after eating a food or drinking a liquid] unless the food/liquid has yet to be digested by the abdomen. One who ate bread or meat [or other food] to the point of satiation [i.e. to the point that he no longer desires to eat anymore] may recite an after blessing so long as he has not yet begun to become hungry due to eating that food. This applies even if many hours have passed, as there is no 72-minute limitation applicable to a meal that one ate to satiation. However, from the moment that he has begun to become hungry, he may no longer say the after blessing. [See Seder 5:9; Admur 184:3] If, however, he did not eat a satiating meal, then an after blessing is to be said within 10 minutes from finishing the food, and if one did not do so then if 96 minutes have not yet passed he is to eat another food and say an after blessing. If 96 minutes have passed, he may no longer say an after blessing. [See Admur ibid; Ketzos Hashulchan 60 footnote 20]
 Kaf Hachaim 89:19
 Yabia Omer 1:4; 3:3; Mishneh Halachos 5:97
 Rav Elyashiv, brought in Hakashrus 10 footnote 76, based on wording of Meiri 5-6 hours.
 Kneses Hagedola 89:6; P”M 89 M”Z 1; Beis Lechem Yehuda 3; Kreisy 89:6; Perech Shushan 89:1; Gan Hamelech 154; Shulchan Gavoa 89:3; Birkeiy Yosef 89:4 [Shiyurei Bracha]; Erech Hashulchan 89:2; Chochmas Adam 40:12; Pischeiy Teshuvah 89:3; Mikdash Me’at 89:1; Zivcheiy Tzedek 89:2; Kaf Hachaim 89:5
 See Kaf Hachaim 89:5
 Peri Chadash
 Daas Kedoshim Butchach 89:2; It is told of the Chasam Sofer that he ruled this way as well and after twice having tried to drink milk after awakening to only have the milk spill, he retracted his ruling. [Hakashrus 10 footnote 77]
 Darkei Teshuvah 89:5
 Yad Yehuda 89
 The reason: As this is consider a Davar Sheyeish Lo Matirin. [ibid]
 Darkei Teshuvah 89 based on that we do not say the concept of Davar Sheyeish Lo Matirin regarding a matter that one can do both today and tomorrow.
 Mishneh Halachos 5:97; Hakashrus 10:33