Shiurim for a K’Zayis

At Shule on Friday night, I read most of the pamphlet put out by Rav Moshe Donenbaum, a Talmid Chacham of note. At the back of the pamphlet there are a series of charts which are meant to simplify the determination of how much Matzah one should consume: related to the size of a Zayis—olive. Expectedly, and it is his right, Rav Donenbaum focusses on the Shiur of the Chazon Ish (the largest) and notes that this is the “best, or most mehudar”. That may well be the case, we aren’t in a position to argue with the great Chazon Ish, let alone any of the other well-known shiurim of R’ Chaim Naeh or the Igros Moshe etc

What does strike me about these pamphlets though is that they seem to completely ignore newer insights into what a Zayis is, based on evidence. There are some incredibly compelling arguments of late which suggest that a Zayis was a lot smaller than what Ashkenazi Poskim (who likely never saw an olive) surmised.

As R’ Bar Chaim put it

Rashi almost certainly never saw an olive. The same goes for other medieval authorities in Ashk’naz (Germany-Northern France). This little-known but indisputable fact should matter to you. It has everything to do with the following question: Is Halakhic Judaism rational and rooted in reality, or is it a hypothetical construct unconducive to engaging the real world?

It is a simple matter to ascertain, or describe to another, the volume of an average olive, a ‘k’zayit’…provided you have olives. But what if you have never seen an olive? How would you understand the concept? How would you describe it to someone unfamiliar with olives?

This was the reality in Ashk’naz in the Middle Ages, and there is no mystery as to why. The olive tree is native to the Mediterranean basin, from Israel in the East to Spain in the west; it does not naturally grow elsewhere. In Roman times, due to the trade routes which crisscrossed the Empire, olives may have made their way to Germany and beyond. The collapse of Rome, however, led to a breakdown of law and order, and therefore trade.

Medieval Ashk’nazim were unfamiliar with olives, a fact confirmed by R. Eliezer b. Yoel’s (d. circa 1225) discussion of the minimal amount required for a b’rakha aharona: “Wherever a k’zayith is required, one needs a sizeable amount of food, because we are unfamiliar with the size of an olive…” (Ra’avya, B’rakhoth 107).

Some Ashk’nazi authorities concluded that an olive was half the volume of an egg, while others demonstrated, based on Talmudic sources, that it must be less than one third of an egg. How much less they could not say. The truth, of course, is different, as was clearly perceived by one 14th century authority who actually made it to Eretz Yisrael. Responding to the proposition that a person could swallow three k’zaytim at once (which is quite impossible if one assumes a k’zayit to be half of an egg in volume) he wrote: “As for me, the matter is plain, for I saw olives in Eretz Yisrael and Yerushalayim, and even six were not equal to an egg.” S’pharadi authorities, on the other hand, had no such difficulties. One wrote that an olive is “much less” than a quarter of an egg (Rashba), while another mentions in passing that a dried fig is equal to “several olives” (Rittba). The last three statements, made by sages who saw olives, are entirely accurate.

In present day Halakhic practice, predicated on opinions rooted in the aforementioned lack of knowledge and experience, a k’zayit is often said to be 30 cc, while others say 60 cc. These figures bear no relation to the real world olives of Eretz Yisrael which average 3-5 cc. It is claimed by some that once upon a time olives were much larger. This claim is false. Olives and olive trees have not changed, as evidenced by the fact that there are over 70 olive trees in Israel ranging between 1,700-2000 years old, and 7 are approximately 3000 years old. These trees continue to produce fruit identical to the olives of younger trees. Halakhic responsa from the G’onic period echo these facts, stating plainly that olives do not change. Some would have you believe that there are two kinds of olives: real olives and ‘Halakhic’ olives. In their view, Halakha need not reflect reality; it exists in an alternate reality of its own. This is a tragedy because it paints Judaism as divorced from reality and irrelevant to a rational person. This is a lie because Torah was intended by Hashem as our handbook for operating in the real world.

An even better analysis, is provided by the unnecessarily derided R’ Natan Slifkin in his excellent article here. I recommend you read it.

Now, I’m aware of the hierarchy of Poskim, and I am aware that one has to have “Breite Pleytzes” but when we are dealing with facts on the ground, we need to re-examine things according the clear scientific knowledge unearthed in our time. This isn’t evolution and a challenge to Ma’aseh B’reishis. It is simply about the humble olive. Was it bigger and did it shrink of late?

Is this any different from the Gemaros in Horayos quoted in Shmiras HaGuf VeHanefesh and Kitzur Shulchan Aruch, which list foods that are claimed to make one forget things, as well as foods which harm other parts of one’s body. If not for the Ari Zal, we wouldn’t even be permitted to eat Chopped Liver! What are the Tannoim telling is in these Gemoras? Are they telling us that this is Halacha L’Moshe MiSinai and avoiding these foods is immutable? No! Perhaps they are actually doing us a great service by informing us what the best medical knowledge of that time was, and it’s our duty to ignore the parts which are discredited and follow the best medical practice of our time? This is certainly R’ Schachter’s strong view. Do we follow the Rambam’s medicine? Decidedly not. If it contradicts evidence-based current medical advice, it might even be forbidden to do so!

So, in our age of the somewhat cryogenic halachic process, where disagreement might be seen tosignal that someone doesn’t have Emunas Chachomim, I wouldn’t expect the types of publications put out by certain institutions to even bother to examine and respond to the cogent arguments suggesting that an olive is an olive is an olive and they simply haven’t changed, given the archeological evidence. We owe it to the pursuit of Emes, though, to be part of our world and also interact with Poskim who are brave enough to put their views on paper for open scrutiny. By all means, disagree, but bring proofs. Simply putting up only a  traditional view derived from sefekos and chumros on the matter without even spilling one ounce of ink on refuting the powerful contrary views, frustrates me. Some would even call it a style of indoctrination which creates a new Mesorah based on Safek cum Chumrah.

On the contrary, perhaps those who follow the approach to sizing an olive based on what we can see, are the ones who follow the original Mesorah, while the others are working in a vaccum of Safek and being Machmir accordingly, given it is D’Orayso?

PS. I was baffled to find a quote attributed to R’ Elyashiv that we don’t need to check the inside of our pockets using a candle during bedikas chametz. Is there a Hava Amina that Chazal would want us to potentially cause fires in our houses, or am I missing something?

Author: pitputim

I've enjoyed being a computer science professor in Melbourne, Australia, as well as band leader/singer for the Schnapps Band. My high schooling was in Chabad and I continued at Yeshivat Kerem B'Yavneh in Israel and later in life at Machon L'Hora'ah, Yeshivas Halichos Olam.

12 thoughts on “Shiurim for a K’Zayis”

  1. Interestingly if we are to go L’Chumra to the measure of a K’Zayis for the Karpas we should make sure that we eat less then the size of an average olive to remove us from the problem of Safek Brocho Acharonah which if you’re eating potatoes it may be easy to go over this shiur’


  2. The problem with R Mandel’s argument is that our sources for the shiurim (leaving aside the Tzlach/Chazon Ish) are many and pretty much unanimous, and almost all of them were familiar with olives. Our sources are not Rashi and the baalei Tosfos.

    As for the Tzlach, whose shiurim the Chazon Ish championed, he probably had no olives, but he certainly had eggs. He decided to double the traditional shiurim because he found a contradiction between the shiurim for length and for volume, and decided that this meant eggs had shrunk over the years. Presumably he’d say the same for olives.

    RACN was not mechadesh anything, he just rallied all the sources for the traditional measurements, and said the Tzlach had just got the lengths wrong by measuring people of unusual size. I’ve even seen a theory that manages to reconcile the Tzlach’s shiurim for length with the Rambam’s shiurim for volume.


    1. There are queen olives(you can see them on the Coles shelves) which are about 3 times the size of the usual olive. If they are around these days, I can’t see why they shouldn’t have been around in “the olden days”


      1. What is your source for stam olives being the largest olive variety? Would one not expect that Chazal would then specify the large variety as opposed to standard variety? We could also breed olives which were huge. What then? Would we have to now increase the size of the Chazon Ish’s Becher, and not just the Chafetz Chaim’s?

        Also, is it your contention that Chazal’s olives were ones which were NOT suitable for producing oil? Seems that’s the case for these Spanish Queen Olives?


    2. The Tzitz Eliezer is irrelevant to this discussion, because he’s merely rejecting the Tzlach’s chiddush of giant shiurim, and upholding the traditional shiurim (as championed by RACN). He is absolutely not supporting Mandel’s chidush to reduce the size of a kezayis. And he certainly knew how big olives are!


  3. For what it’s worth, I find it had to believe that Rashi (who lived in France) never saw an olive. Was he devoid of curiosity? Were they never traded as far north as Troyes? Did he never look at a pickled olive?


  4. Milhouse – – Whilst I don’t disagree with you on the halocho le’maaseh, you are wrong in the theory. The Rishonim who were familiar with the size of olives do not refer to eggs when describing kezeisim, and this is recognized by two of the leading Charedi mumchim on shiurim of our times, Rav Benish (who published this view in Beis Aharon V’yisroel) and Rav Hadar Margolin. This theory was also advocated by the great Rav Akiva Yosef Schlesinger. See my comment here:


Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: