The Rama on Orach Chaim 494:3 quotes a widespread minhag to eat dairy foods on Shavuos. The Mishnah Berurah (ibid. s.k.12) proffers the famous explanation for this custom: Bnei Yisroel, upon receiving the Torah on Shavuos, were unable to eat meat right after the Torah was given. There was no time to prepare and check shechitah knives, remove blood and cheilev (non- kosher fats) from meat, and kasher utensils needed to cook and prepare hot meat. Thus, it was necessary on that first Shavuos to consume cold dairy foods. We therefore commemorate this event by also partaking of dairy dishes on Shavuos.
The Rama himself offers another rationale for eating dairy food on Shavuos: The Korban Shtei HaLechem is commanded to be brought on Shavuos; we therefore eat both dairy and meat foods on Shavuos, as this will require us to have two different breads (because we cannot eat the same bread with dairy and meat foods); the two breads necessitated by serving dairy and meat dishes, served on the table, which symbolizes the mizbayach commemorate the Korban Sh’tei HaLechem. (MB ibid s.k.14)
There are some other, less-known explanations as to why we eat dairy foods on Shavuos:
• Moshe Rabbeinu was taken out of the Nile on Shavuos and was thereafter brought to be nursed, and he refused to drink milk from non-Jewish women.
• The gematria of chalav is 40, corresponding to the forty days that Moshe was on Har Sinai.
• One of the names of Har Sinai is Gavnunim, similar to the word gevinah – cheese.
• The Chok Yaakov (OC 494:9) quotes the Kol Bo (s. 52) that the minhag is to eat both honey and milk on Shavuos, as the Torah is compared to honey and milk (Shir HaShirim 4:11).
The custom of eating dairy foods on Shavuos, however, remains cryptic and is not mentioned by many halachic sources, and that is why there are so many possible explanations. (Note that the Rama explains the basis for the custom with a partial conjecture, “and it seems to me that the reason is…”, rather than stating a definitive rationale, as this minhag is of unclear background.)
The most common methods whereby people fulfill the custom to eat dairy foods on Shavuos are by having dairy Yom Tov meals or by serving dairy Mezonos foods after making Kiddush on Shavuos morning (and consuming a regular Yom Tov seudah later). This latter method is suggested by the Darchei Teshuva (YD 89, s.k. 19) as the ideal way to fulfill the minhag of eating dairy foods on Shavuos while partaking of a most proper Seudas Yom Tov. Each of these approaches requires a bit of halachic analysis.
DAIRY MEALS ON YOM TOV
When the Beis Hamikdash stood, the mitzvah of Simchas Yom Tov (Rejoicing on Yom Tov) was fulfilled by partaking of the Korban Shelamim. However, when there is no Beis Hamikdash, the mitzvah of Simchas Yom Tov is expressed in alternative forms. (See Pesachim 109a.)
The Rambam (Hil. Yom Tov 6:18) states that – in addition to eating the Korban Shelamim – the mitzvah of Simchas Yom Tov is fulfilled by men partaking of meat and wine, women wearing fine clothing and jewelry, and children partaking of treats. The Tur (OC 529) quotes the Rambam’s requirement to eat meat, but the Beis Yosef and Shulchan Aruch (OC 529:2) have difficulty with the Rambam’s ruling and opine that there is no mitzvah to eat meat on Yom Tov in the absence of the Beis Hamikdash, for the Gemara (Pesachim 109A) states that once the Beis Hamikdash was destroyed, simcha is only with wine. The Beis Yosef explains that since eating meat for Simchas Yom Tov is only mandated when one brings and consumes a Korban Shelamim, and that in the absence of the Beis Hamikdash, the mitzvah of eating meat thus should not pertain. The Bach (ibid. d.h. Kasav HaRambam) and others disagree and maintain that one should eat meat, even though it is not from a Korban Shelamim, as there is nonetheless a secondary concept of simcha that is obtained by eating meat, notwithstanding that it is not from a Korban and that the simcha obtained by eating meat is not the primary Simchas Yom Tov in the absence of a Korban Shelamim.
The Mishnah Berurah concurs with the Bach and advises to eat meat on Yom Tov. (See Biur Halacha ibid. d.h. Keitzad.) The Bach and Mishnah Berurah hold that although one technically fulfills the mitzvah of Simchas Yom Tov even without eating meat, there is an enhancement of the mitzvah when meat is consumed.
When applied to Shavuos, one who follows the Bach and Mishnah Berurah should ideally eat a meat meal rather than a dairy meal on Yom Tov day, despite the fact that he technically fulfills the mitvzah of Simchas Yom Tov with a dairy seudah. One who goes according to Beis Yosef and Shulchan Aruch would be advised to eat whatever type of meal he most prefers. According to the Beis Yosef and Shulchan Aruch, one can lechatchilah eat poultry as his main course, whereas the Bach and Mishnah Berurah seem to hold that beef is preferred, as they note the idea of simcha being identified with basar, meaning “meat” proper.
(There is an alternative interpretation of the Rambam, as submitted by some Torah authorities, including Rav Chaim Brisker zt”l, who explain that the Rambam mandates two levels of Simchas Yom Tov: an objective one, consisting of eating Korban Shelamim, as well as a subjective level, such that all people should experience the simcha of the festival as they personally prefer. This is why the Rambam writes that women should fulfill the mitzvah of Simchas Yom Tov by wearing fine clothing and jewelry, and that children should partake of treats – as this level of the mitzvah of Simchas Yom Tov is subjective according to the individual, and there is no one uniform rule for all people. This approach maintains that eating meat is merely an illustration of that which generally engenders simcha, but that there is no mitzvah to partake of meat per se according to the Rambam. Hence, the mitzvah of Simchas Yom Tov can be fulfilled by engaging in any act that brings one to simcha, according to this interpretation of the Rambam, although one must of course fulfill the mitzvah of Seudas Yom Tov, irrespective of the choice of foods he decides to serve.)
PARTAKING OF “MEZONOS” FOODS AFTER KIDDUSH
There is a fundamental principle of ain Kiddush ‘ela bim’kom seudah – Kiddush may only be made at the site of the meal  . Regardless of the rationale for the axiom of ain Kiddush ‘ela bim’kom seudah, one who makes Kiddush without a meal (i.e. he does not eat a seudah after Kiddush, or he recites Kiddush in a location other than where he eats the meal) does not fulfill the mitzvah of Kiddush and must make Kiddush again when and where he eats.
The Tur and Shulchan Aruch (ibid. s. 5) quote the Geonim that one can fulfill the mitzvah of Kiddush without actually eating a full meal at the time and place that he makes Kiddush. Rather, posit the Geonim, a person can consume a mere kezayis of bread or even drink an additional revi’is of wine as his Kiddush-time “meal”, so that he fulfills the requirement of Kiddush bim’kom seudah. The Magen Avraham (ibid. s.k. 11) and Aruch HaShulchan (ibid. s. 8) explain that, according to the Geonim, one can eat what we refer to as Mezonos foods after Kiddush and satisfy the rule of ain Kiddush ‘ela bim’kom seudah. This interpretation of the Geonim’s opinion has become widely accepted, and many poskim permit partaking of Mezonos foods after Kiddush but advise against satisfying the mitzvah by merely drinking an additional revi’is of wine. (See MB ibid. s.k. 25.)
The overall position of the Geonim is one of dispute, as the simple interpretation of ain Kiddush’ela bim’kom seudah is that one must actually have his seudah – a full meal with bread – upon making Kiddush, and some therefore advise that one is best not relying on the Geonim’s approach  . However, the more prevalent practice is to rely on the Geonim’s view and make Kiddush followed by cake or other Mezonos foods.  If one follows common custom (the opinion of the Geonim), it would seem that he can satisfy the minhag of consuming dairy food on Shavuos by eating cheesecake after Kiddush on Shavuos morning. However, it is not so simple.
The approach of the Geonim only postulates that Mezonos food eaten after Kiddush satisfies the requirement of Kiddush bim’kom seudah when the amount of Mezonos food is at least a kezayis. (See MB 273: 21) The problem is that many types of cheesecake have very little flour, and one does not typically consume a kezayis of the dough or flour part of a slice of such cheesecake in the requisite period of k’dei achilas p’ras, “the time it takes to eat a piece of bread” (which, according to Rav Moshe Feinstein zt”l, would be under 3 minutes – Igros Moshe 4:41). Thus, cheesecake with minimal dough/flour content would not seem to qualify as the Mezonos food to eat after Kiddush.
Additionally, even though the b’racha rishona for cake and pie is Mezonos, even when the majority of the cake or pie consists of filling or fruit rather than flour, there is an exception when the flour or dough part of these desserts serves merely to hold the filling or fruit in place and is not intended to provide flavor (OC 208:2). Some cheesecakes are virtually all cheese, and they have a paper-thin layer of tasteless dough which merely keeps the cheese in place. This situation would warrant reciting a Shehakol and would likely not enable one to consume the cheesecake directly after Kiddush. (See OC 208:9 and MB ibid. s.k.45.)
Should one wish to have cheesecake after morning Kiddush,the solution would be to either purchase a cheesecake that has sufficient dough/flour (a kezayis worth that will be consumed within the shiur of k’dei achilas p’ras), or to also eat a kezayis of another type of Mezonos food (e.g. cookies, pastry or cake), making sure to have a kezayis of the Mezonos food in a period of k’dei achilas p’ras, as above. In case one wishes to consume a Shehakol cheesecake, he should first eat a kezayis of Mezonos item right after Kiddush prior to eating the Shehakol cheesecake.
EATING MEAT AFTER MILK
What is the halacha if one makes Kiddush and eats dairy foods, planning to later eat a meat Seudas Yom Tov? What if one partakes of a dairy Yom Tov seudah at midday and plans to eat a meat seudah shlishis later? How does one transition from milk to meat?
The Gemara in Chullin (105a) quotes Rav Chisda, who states that one need not wait at all after eating cheese before consuming meat. However, if one consumes cheese and then plans to eat meat (as opposed to poultry), one must ascertain that his hands are clean, and he must cleanse and rinse his mouth. The Gemara’s discussion there elaborates on what constitutes proper kinuach (cleaning of the mouth) and hadachah (rinsing of the mouth). The Shulchan Aruch (Yoreh Deah 89:2) invokes the Gemara’s discourse on this topic.
One must cleanse his mouth (kinuach) and rinse it (hadachah); kinuach  involves chewing bread, thereby cleansing the mouth very well. One may perform kinuach with anything that he desires, except for flour, dates and vegetables, since they adhere to the gums and do not cleanse well. And then one must rinse his mouth with water or wine. This is only for basar behemah or chayah, but for poultry, there is no need for any cleaning or washing of hands.
The above procedures appear pretty simple. However, the commentaries of the Shulchan Aruch add a few noteworthy caveats.
The Shach (s.k.9) quotes the Rif’s position that one should always wash his hands after eating cheese before partaking of meat and not rely on visual inspection of the hands, as one cannot really tell if his hands are truly free of residue by merely looking at them; the Shach further quotes the Iturei Zahav, who states that this is the common custom. In practice, one should conduct himself according to this position and always be sure to wash his hands after eating dairy foods before consuming meat.
The Be’er Hetev (s.k.5) notes that the Pri Chodosh maintains that one need not wash his hands before meat if he ate cheese with a fork; it appears that the Be’er Hetev rules this way as a matter of practical halachah. The Aruch HaShulchan (89:8) concurs with the Pri Chodosh in this matter, and this is the accepted halachah.
Although the Shulchan Aruch rules that one must first perform kinuach and then do hadachah, the Shach (s.k.13) and Be’er Hetev (s.k.7) contend that the order does not matter. The Shach invokes the position of the Beis Yosef (Tur 89:11) that one may perform kinuach and hadachah in whichever order he prefers. The halachah is according to the Shach on this point, and one may perform kinuach and hadachah in the order of preference or convenience.
Once one has finished eating dairy food and has performed kinuach and hadachah and has cleansed his hands, may he eat meat right away? The Gemara does not stipulate any waiting period. In fact, the Shulchan Aruch (YD 89:2) notes that one may eat meat miyad – immediately – and the Rif, Rambam and Tur also do not record any requirement for a waiting period. However, the Zohar in Parshas Mishpatim (155a) indicates that one must recite the bracha acharonah after a dairy meal and then wait before being permitted to consume meat. Many conduct themselves as such and wait half an hour or an hour in light of the Zohar’s position, although the bottom-line halachah is not to require any such waiting period.
The above pertains only to one who ate a dairy meal and then wishes to eat ”meat” in the true sense of the word, such as beef, veal or venison. Poultry requires no washing of hands nor cleansing and rinsing of the mouth when eaten after dairy foods.
by Rabbi Avrohom Gordimer
 Pesachim 101a, Rambam Hil. Shabbos 29:8, Shulchan Aruch OC 273:1
 See Aruch Ha-Shulchan and Bi’ur Halacha ibid.; Hag. Rabbi Akiva Eiger on Magen Avraham ibid. s.k. 10.
 Some halachic authorities, including Rav Yosef Dov Soloveitchik, have ruled that if one makes Kiddush and then eats Mezonos foods, he must make Kiddush again later at his actual seudah.
 Although the Gemara and Shulchan Aruch stipulate that kinuach is done with food, may a person fulfill the requirement of kinuach by brushing his teeth instead? This issue is not widely discussed by poskim, although the issue is debatable and should be referred to one’s individual rabbi. There is a view that brushing teeth does not constitute kinuach, as a toothbrush does not rub against the insides of the mouth to cleanse it as does food; others argue that tooth brushing is fully effective.
 Nevertheless, one must be very careful with this exception, as all too often food eaten with utensils somehow ends up on one’s hands. This almost inevitably happens in the course of eating, serving or cleaning up after a meal.