Shiur # 47: Berakha Acharona Ke-Zayit – Volume or Weight

  • Rav David Brofsky


In memory of our parents, Helen and Benjamin Pearlman z”l and Jack Stone z”l,
and in honor of my mother, Esther Stone, Yibadel Le-Chayim Tovim
by Gary and Ilene Stone





As we have noted, one only says a berakha acharona after eating the equivalent of a ke-zayit (see Berakhot 37b, Shulchan Arukh 210:1).


Last week, we discussed the size of a ke-zayit. We learned that some Ashkenazic Rishonim (Tosafot, Eiruvin 80b, s.v. agav; Ra’avia 525; Terumat Ha-Deshen 139; and the Maharil, Seder Ha-Haggada 31), based upon an apparent contradiction between two passages (Yoma 80a and Keritut 14a), rule that a ke-zayit is the size of half of an egg (ke-beitza). Most Rishonim, however, do not accept this large measurement. The Rambam (Hilkhot Eiruvin 1:9), for example, implies that a ke-zayit is less than 1/3 of an egg. Some Acharonim took this to mean that one should assume that a ke-zayit is approximately 1/3 of an egg.


The Shulchan Arukh (Hilkhot Eiruvin 378:3, 409:7) rules in accordance with the Rambam, implying that a ke-zayit must be smaller than a third of an egg. However, regarding the laws of matza (486), he writes: “Regarding the size of a ke-zayit, some say (yesh omrim) that it is half of an egg.” The Acharonim discuss this apparent contradiction, as well as the phrase “some say” in the context of matza. Some (see, for example, Mishna Berura 486:1 and R. Chaim Naeh, Shiurei Torah, p. 190, n. 24) suggest that the Rambam is strict regarding mitzvot de-oraita (Biblical mitzvot), such as matza, and most probably a berakha acharona as well, due to the principle of safek berakhot le-hakel. Others (see R. Chaim Benish, “Shiur Ke-ZayitBi’ur Da’at Rishonim Ve-Acharonim,” who cites numerous Acharonim) suggest that the Shulchan Arukh did not intend to rule against the Rambam and the prevalent custom, but rather merely to cite the only explicit shiur that appears in the Rishonim.


Assuming that one says a berakha acharona only upon eating 1/3 or 1/2 of a ke-beitza, the Acahronim offer different estimates as to the size of a ke-zayit in relation to a ke-beitza. Based upon traditional measurements of a ke-zayit and the Rambam’s mention of a ke-beitza relative to an amount of Arabic coins known as drahms, R. Chaim Naeh (1890–1954), in his “Shi’urei Torah,” half of a ke-beitza without its shell (54.7 cc) is 27 cc, and that is therefore the size of a ke-zayit according to Tosafot. According to the Rambam, a ke-zayit is a third of an egg, with or without its shell – 19.2 cc or 17.3 cc accordingly.


We also noted that R. Yechezkel Landau (1713 –1793), author of the Noda Be-Yehuda, questioned the commonly accepted size of an egg based upon another method of measuring that appears in the Talmud (Pesachim 109a-b). He suggested that olives and eggs have “become smaller” over time. R. Avraham Yeshayahu Karelitz (1878–1953), known as the Chazon Ish, adopted the position of the Noda Be-Yehuda. In his Kuntras Ha-Shiurim (OC 39), he concludes that since the volume of a ke-beitza is 100 cc, according to Tosafot, a ke-zayit is 47.5 cc (1/2 of an egg without its shell) and according to the Rambam, it is 33 ml (1/3 of an egg with its shell). Although some Acharonim recommend adopting this view when fulfilling a Biblical mitzva, such as eating matza, most assume that it is customary to follow the opinion of R. Chaim Naeh – 27 cc (1/2 of a ke-beitza) or 17 cc (1/3 of a ke-beitza). Many halakhic compendiums write that one should measure a portion of food against a standard match box, approximately 25-30 cc (5X3.5X1.5); a plastic bottle-cap is approximately 10 cc.


Interesting, most Rishonim do not believe that the ke-zayit should be measured in comparison to the egg, and they assume that one simply measures against a contemporary, mid-sized olive.


This week, we will discuss whether one measures a ke-zayit by volume (nefach) for weight (mishkal), and question whether one measures the entire food or only the relevant ingredients (i.e. flour in a cake). We will also note that the ke-zayit of food must be eaten within an amount of time known as kedei akhilat peras, which we will attempt to define.


Volume or Weight


The Talmud in numerous places implies that the volume (nefach), and not the weight (mishkal), is the determining factor in measuring shiurim. For example, the gemara (Pesachim 109a-b) defines the liquid measure of a revi’it, which is equivalent to an egg and a half, as 2 fingerbreadths X 2 fingerbreadths X 2.7 fingerbreadths. Similarly, the mishna (Uktzin 2:8), which we will return to shortly, teaches: “An airy loaf is evaluated as it is. If there is a hollow inside, it is compressed.” Finally, the Tosefta (Nazir 4:1) describes how one places a ke-zayit aguri in wine and drinks the displaced wine, clearly indicating that a ke-zayit is measured by volume and not weight (see Rashi, Chullin 108b, s.v. chalav).


The Geonim also clearly believed that a ke-zayit was measured by volume. They write (Teshuvot Ha-Geonim, Harkavy 268):


And if you were to suggest [that they be measured by] weight, the Rabbis did not specify weight and Ha-Kadosh Barukh Hu did not exact with us in weight; [rather,] every person who estimates according to his evaluation has fulfilled his obligation


The Geonim note that it is virtually impossible for every person to know the measurement of every food. Rather, a person is to estimate according to size.


The Rambam (Commentary to the Mishna, Challah 2:6; Hilkhot Chametz U-Matza 5:12) also clearly rejects measuring shiurim by weight. The Maggid Mishna (ibid.) explains that the weight is not always similar to the volume, and therefore the shiurim clearly refer to volume and not weight.


The Shulchan Arukh (456:1) cites the Tur, who describes determining the shiur of challa thought the displacement of water. Furthermore, the Rema (486:1) implies regarding the shiur of maror that one estimates the proper shiur based upon volume. 


Interestingly, R. Yaakov Chaim Sofer (1870–1939), in his Kaf Ha-Chaim (Orach Chayim 168:45-46), asserts that “it is unlikely that it is dependent upon the evaluation of each person, as he sees it.” After citing a number of Sephardic authorities, he concludes: “It is not the common custom among halakhic authorities to estimate all measurements, such as a ke-zayit of matza on Pesach, and a ke-zayit of maror, and a ke-zayit for the measurement of a berakha acharona … by weight… and this should not be changed.” Numerous Sephardic authorities rule that a ke-zayit is measured by weight, such as the equivalent of 27 grams, although they assume that weight is only used as a means of properly determining the volume equivalent of a ke-zayit, as weight and volume are generally similar. Other Sephardic authorities (Ohr Le-Tzion, vol. 2 ch. 14, n. 17; Yalkut Shemesh 137; see also Machzikei Berakha 486:2) disagree and insist that one measure the size of a ke-zayit based upon nefach.


Assuming that one measures a ke-zayit according to a food’s volume, does it matter if a food is light or dense?  Does one include air pockets in the measurement of a ke-zayit


As mentioned above, the mishna (Uktzin 2:8) teaches: “An airy loaf is evaluated as it is. If there is a hollow inside, it is compressed.” This mishna implies that while the food should be compressed if there is an air pocket,, generally speaking, we do not take the density of a food into consideration.


Most Acharonim assume that if a food is naturally light or fluffy (bread, popcorn, etc.), one still measures by its volume (see Mishna Berura 186:3). R. Ben Zion Abba Shaul, in his Ohr Le-Tzion (ibid.), rules that airy or fluffy foods should always be condensed.


What if a food absorbed water after it was prepared, and then expanded? Does it matter if the food was originally that large and subsequently shrunk (i.e. raisins) and became enlarged again or if it was always small and simply expanded?


The Rambam (Hilkhot Ma’akhalot Asurot 14:5) writes:


When an olive-sized portion of forbidden fat, a nevela, piggul, notar, or the like was left in the sun and was reduced in volume, one who eats it is not liable.


The Rambam clearly believes that a ke-zayit is determined by its current size. However, he adds:


If afterwards one left it in the rain and it expanded, one is liable for either karet or lashes. If originally it was smaller than an olive-sized portion and then expanded to the size of an olive, it is forbidden to partake of it, but one is not liable for lashes for it.


Here, he indicates that if a food returns to its original size (i.e. such as raisins soaked in water), then we follow the current volume. If, however, the food absorbed water and grew to a larger, unnatural volume, we follow the original size.


Indeed, this appears to be the ruling of R. Yishmael ben Avraham Yitzchak Ha-Kohen (Italy, d. 1811) in his Zera Ha-Emet (29). Similarly, the Mishna Berura (210:1) rules:


If there is an airy loaf that expanded until the air pocket are no longer noticeable, one who eats a ke-zayit of it does not say a berakha acharona, because in truth, he did not eat a ke-zayit. Similarly, if there was a ke-zayit and it depressed and became smaller, one does not say a berakha [acharona] over it unless it becomes bigger again.


The Mishna Berura refers here to bread that after baking expanded even more. Elsewhere (486:3 and Sha’ar Ha-Tziun 7), he rules that regarding matza, if its air pockets are not noticeable, there is no need to compress them.




The mishna, Rishonim, and most Acharonim clearly rule that one should estimate the size of a ke-zayit based upon volume (nefach). Volume includes natural pockets of air, which are not noticeable. If they are noticeable, the food should be condensed in order to determine its volume. Some Sephardic authorities maintain that one should measure according to weight, as it is often difficult to assess the size of a piece of food.


R. Eliezer Melamed writes in his Peninei Halakha (Berakhot, pg. 217):


Every person should learn to evaluate the volume of foods in relation to half an egg… And we already learned that a person does not have to be overly concerned, as the Rabbis assigned each person the authority to estimate the measurement itself, despite the probability that a person may err a bit above or below.


Although we noted above that many assume that the measurement is less than a third of an egg and others even measure against an olive itself (4 -6 cc), his sentiment is still worth considering.



            Next week, we will continue our study of the berakha acharona