Washing and Al Netilas Yadayim on less than a Kebeitza of bread:^[1]
If one will not be consuming a shiur Kibeitza without its shell[2] [53.8 grams^[3]] of bread within two times Kdei Acilas Peras [i.e. within 8 minutes^[4]], each Kezayis within Kdei Achilas Peras[5] [i.e. 4 minutes[6]], then one is to wash without a blessing prior to eating this bread.[7] This is despite the fact that he will say Hamotzi [on any amount he eats] and Birchas Hamazon [if he eats a Kezayis of the bread within 4 minutes]. One must be particularly careful in this matter by the third Shabbos meal.[8] This applies even if one will be holding in his hand a piece of bread that is larger than a Kibeitza, nevertheless if he eats less than a Kibeitza he is to wash his hands without a blessing.[9] This applies no matter how much bread he eats that is less than a Kibeitza, even if it is a very small amount, in all cases he is to wash without a blessing.[10] If one will be consuming a total of a Kibeitza [within Achilas Peras[11]] then he is to wash with a blessing even if he will be eating a small amount at a time, even if he eats small crumbs that total of a Kibeitza.[12] [Due to the above ruling, it is important that when one begins his meal, to focus on eating a Kibeitza of bread within the first eight minutes rather than eat the bread slowly and partake in other foods at the same time.[13]]

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[1] Admur 158/2 “It is questionable…therefore one is to wash without a blessing”; Seder Netilas Yadayim 18 “If wash but will not eat Kibeitza, dont say a blessing”; Michaber 158/2; Rokeiach 328; Ketzos Hashulcahn 36/2; Piskeiy Teshuvos 158/7

Other opinions: Some Poskim rule one may wash with a blessing on a Kezayis of bread. [Shaar Hatziyon 158/9 in name of Gr”a in Biur Hagr”a 158; Igros Moshe 4/41 regarding time of need based on Gr”a; See Vezos Haberacha p. 15 and 347; See Ritva on Sukkah 25a]

[2] Admur 158/2; Omitted in Seder; Degul Merivava 158; M”B 158/9; Kaf Hachaim 158/8; See Rambam Tumas Ochlin 4/1; Eiruvin 83a

[3] Shiureiy Torah 3/9; This is opposed to a Kibeitza with its Kelipa which is a Shiur of 57.6 grams; See Shevet Halevi 6/60; Pisckeiy Teshuvos 158/7 who writes 57 grams

[4] See Seder Netilas Yadayim 18 that each Kezayis must be eaten within Achilas Peras, [4 minutes] and see Ketzos Hashulchan 36 footnote 5 and Shiureiy Torah 3/9 in name Reb Yisarel Noach that the second Kezayis must be eaten immediately after the first Kezayis.

[5] Seder Netilas Yadayim 18; Omitted in 158/2 that one must eat the Kebitza within 8 minutes [See Seder Netilas Yadayim of Rav Alyashvili footnote 230 who learns according to Admur in the SHU”A there is no need to eat it within Peras.]; Tehila Ledavid 158/1; Ketzos Hashulchan ibid; Shenos Chaim 239; Kaf Hachaim 158/9; Piskeiy Teshuvos 158/7; See Kerisus 13; See Siddur Raskin Miluim p. 720 and footnote 230 in new Seder Netilas Yadayim of Rav Alyashvili

[6]  This follows the Shiur that each Peras is 4 minutes:

Four minutes: Shiurei Torah 3/15 [p. 303]; Aruch Hashulchan 202/8; Kaf Hachaim 210/5; Piskeiy Teshuvos 210/1 that so is the widespread custom

Opinion of 6-7 minutes: The Tzemach Tzedek [Shaar Hamiluim 1/8-10] records 6-7 minutes regarding the Shiur of Achilas Peras. [Ketzos Hashulchan 36 footnote 5; 59 footnote 4; Shiureiy Torah ibid footnote 35; Sefer Haminhaghim [English] p. 93 regarding Tishe Beav] In Shiureiy Torah ibid footnote 35 he concludes that if one ate 17 grams in the first 4 minutes and completed 28 grams in 8 minutes, he may say Birchas Hamazon.

Three minutes-Chabad custom: See Sefer Haminhagim ibid and footnotes 342-344 for a quote of various opinions of Achilas Peras, and for a tradition from the Tzemach Tzedek, in name of Rav Hillel Miparitch, that differs from the response of the Tzemach Tzedek which placed Achilas Peras as 6-7 minutes and rather places Achilas Peras as minimum 3 minutes and maximum 7 minutes. The Rebbe concludes there in the footnote that one is required to suspect for the above tradition. So also rules Igros Moshe 4/41 that Achilas Peras is 3 minutes regarding Bracha Achrona. Accordingly, one should try to eat the Kezayis within three minutes. However if one ate it within four minutes, and perhaps even within 6-7 minutes, one can rely on the Tzemach Tzedek’s other rulings. Vetzaruch Iyun, as perhaps Safek Brachos Lihakel. In any event one is to be very careful in the above.

Other opinions: See Shiurei Torah 3/15; Sefer Haminhagim ibid and footnotes 342-344; Piskeiy Teshuvos 158/7 and 210/1

[7] The reason: It is questionable as to whether one who eats less than a Kebeitza of bread is required to wash his hands due to the following reason: Less than a Kibeitza is not considered food with regards to Tumas Ochlin and due to this if an impure person touches food or liquid that is less than a Kibeitza he does not make it impure. [Yuma 80a] This is learned from the verse [Vayikra 11/34] “Mekol Haochel Asher Yochel”, which teaches us that the food must be an amount that is called food [that satiates, which is a Kibeitza]. [Now, perhaps the Rabbinical obligation to wash for bread follows similar rules as] the Sages only required washing hands for Chulin due to Serach Teruma, and this obligation was only made intact when one eats the food and not when one touches it. [We thus see that the entire obligation was on food and] less than a Kibeitza, since it is not considered food regarding Tuma, it is also not considered food regarding washing hands. [However, one can also argue that once the Sages made their decree, they did not differentiate in this matter. Practically, due to this doubt that perhaps the definition of food regarding washing follows the same definition regarding Tuma] therefore one is to wash without a blessing. [Admur ibid; Taz 158/3; Olas Tamid 158/3; Mateh Yehuda 158/3; Beis Yosef 158; See Ketzos Hashulchan 36 footnote 4 and 6 who differentiates between the reason given by the Bies Yosef and that of Admur, and explains how Admur’s explanation answers two strong questions applicable in the explanation of the Beis Yosef; See also Machatzis Hashekel 158/3 and PP”M 158 A”A ]

[8] Seder ibid

[9] Admur 158/2

The reason: As he is not eating an amount of bread that is considered food with regards to Tumas Ochlin. [Admur ibid] The novelty here is that the Sages did not make their decree on the amount of bread one is holding but rather on the amount that one is eating [Ketzos Hashulchan 36 footnote 6]

[10] Admur 158/2; M”A 158/4; Elya Raba 158/3; Divrei Chamudos Chulin 8/72; M”B 158/10

Other opinions: Some Poskim rule that one is not required to wahs hands at all when eating less than a Kezayis of bread. [Shulchan Hatahor 158/12]

[11] Seder ibid; Poskim ibid; Omitted in 158/2 that one must eat the Kebitza within 8 minutes [See Seder Netilas Yadayim of Rav Alyashvili footnote 230 who learns according to Admur in the SHU”A there is no need to eat it within Peras.]

[12] Admur 158/2; Kaf Hachaim 158/9

The reason: As although the crumbs do not join for a size of a Kibeitza in regards to impurifying food, nevertheless, since he is entering into his abdomen an amount that is considered food regarding Tuma of food, therefore his eating is considered food also regarding washing hands. [Admur ibid] This ruling applies only according to the reason offered by Admur, however according to the reason written by the Bies Yosef, one can argue that a blessing is not said unless one enters a full Kibeitza into his mouth at a time. [Ketzos Hashulchan 36 footnote 6]

[13] See Piskeiy Teshuvos 158/7; Shaar Hatziyon 210/10; Maharsham 8/31; Birchas Shamayim 1/17

[14] Ketzos Hashulchan 36 footnote 7; Machazik Bracha Kuntrus Achron 1; Shaareiy Teshuvah 158/1; Ritva Chulin 106, brought in Kaf Hachaim ibid regarding one who washed with a blessing and then decided not to eat bread; Chazon Ish 25/8; See Piskeiy Teshuvos 158/6 footnote 23

[15] The reason: As when the blessing was recited it was njot in vain, since one planned on eating, and whetehr or not one eats in the end does not affect the blessing. [Poskim ibid]

[16] See Sdei Chemed Mareches Brachos  29, brought in Kaf Hachaim 158/6, regarding one who washed with a blessing and then decided not to eat any bread, and that the rules one is not to do so.

[17] The reason: As one may not enter himself into a doubt. One cannot say that such a case is a Sfek Sfeika, as a) some Poskim rule that even by Sfek Sfeika we rule Lihakel and b) One may never initially enter himself into a Sfek Sfeika [see Taz Y.D. 122/8] See however Shevet Hakehasi 5/39