If the time required to wait between eating meat and milk is based on the scientific definition of digestion, why don't we ask today's experts and set a defined time for everyone instead of different people following different customs?

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    This questioned IMHO would be better expressed as "why don't we change our customs to fit science?" Jul 5 '12 at 13:48
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    Because it's not based on the scientific definition of digestion, if one exists anyway. How would you decide when the food is "totally" digested? When x% of the molecules have been converted to waste? When x% of the waste molecules has been expelled from the body?
    – Seth J
    Jul 5 '12 at 13:49
  • @SethJ I'm guessing a Gastro probably has an accurate definition of this. If it's not based on digestion what is it based on?
    – user1668
    Jul 5 '12 at 14:01
  • @PM good question. It's a bit of a controversy. machonshilo.org/en/eng/list-audio-shiurim/41-audiohalakha/…
    – avi
    Jul 5 '12 at 14:16
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    Re "why don't we ask today's experts and set a defined time for everyone": Suppose we could get a good modern-science definition of digestion. Why do you think everyone would do that in the same amount of time? I doubt it.
    – msh210
    Jul 5 '12 at 16:10

Waiting six hours is not based on the scientific definition of digestion. The Talmud (Chullin 105a) says that one must wait from one meal to the next. There is a disagreement among the Rishonim if that actually means from one meal to the next, or if it means the amount of time between the morning and evening meals, which would mean approximately six hours. See YD 89. The reason for the wait according to these Rishonim is either that fat/grease from the meat that is in one's throat emits a meat flavor into one's mouth for a long time (Rashi) or that for that amount of time we are concerned that small pieces of meat might be stuck between one's teeth (Rambam). Neither of these reasons say that these issues last exactly six hours, but rather that the Sages drew a line at six hours, and neither of them have to do with digestion per se.

  • then how can people have different customs? why would the time change depending on things like 'hard' cheese?
    – user1668
    Jul 5 '12 at 16:09
  • @PM The customs of 5, 5.5, and 6 hours are just technical interpretations of how to apply the six hour rule. The customs less than that have no real basis in halacha - what they are trying to do is make some sort of compromise between the Rishonim who hold its a time thing and those who hold its only about starting the next meal (Maharai quoted by the Rema in Darkei Moshe). Hard cheese is a completely different story - that is a later custom that the Talmud never mentions. The custom to wait is simply based on the fact that it has a strong taste that remains in ones mouth for a while.
    – Dov F
    Jul 5 '12 at 16:16
  • @DovF Customs to wait less or more than 6 hours most certainly DO have their basis in Halacha. Today, we eat 3 meals a day, not 2. So the time between breakfast and lunch can be only 3 hours. The talmud states that you don't have to wait anytime at all, but rather just until you sit at a new table. This gets translated into "1 hour" for the sake of people who demand a time. (It takes about 1 hour to eat and clean up a "proper" meal) And there a myriad of other opinions on the topic as well.
    – avi
    Jul 5 '12 at 16:20
  • @avi You are ignoring the Rema I cited. Learn the Rishonim, look up the Darkei Moshe and then we'll talk.
    – Dov F
    Jul 5 '12 at 16:24
  • @DovF I've learned the Rishonim, and the Achronim, and the Geonim, and the Amorim... and I'm not sure how the opinion of the Rema negates the opinion of Rav Chisda. I'm not ignoring anything, I'm just disagreeing that the Rema is the only valid halachic source on the topic.
    – avi
    Jul 5 '12 at 16:32

For Ashkenazim at least, the halacha is like Tosafot, that once one finishes the meat meal, if he starts a new meal he may consume dairy. However, in the common case, people follow their minhag of how long to wait. See the Rama in Shulchan Aruch Yoreh Deah 89:1, as I've seen it traditionally understood -- that he paskens like the יש אומרים that one needs not wait, but that it is a מנהג הפשוט במדינות אלו to wait, rather than a decided halacha -- such that in cases of great need, this minhag may be relaxed.

If so, the science won't help.

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