Mori Yusef Qafih z”l compiled a sefer entitled Ra`avad Teshuvot Ufesakim (ראב”ד תשובות ופסקים). While reading through it, I found the following – very interesting – passage:
נ”ב: כרי חטים שנפל עליו דלף מעט בשאר ימות השנה במקומות מועטין ואותן החטים שנפלו עליו מעורבין בתוך הכרי בטלין הן ברוב ואין צורך לבערן בפסח וביטול בעלמא סגי להו ואפילו לכתחילה ואף על פי שחמץ אוסר בכל שהו הני מילי כשהו בעין לענין לאכלו בפסח ולא נתבטל קודם זמן איסורו אבל מאחר שנתבטל קודם הפסח ברוב אינו חוזר וניעור ואפילו לכתחילה מותר
“52: A pile of wheat [kernels] that a small trickle has fallen upon during the rest of the days of the year [i.e. not during Pesah] in a few small areas, when that wheat becomes mixed in the pile it is nullified in a majority [batelin hen ba-rov] and there is no need to destroy such [kernels] on Pesah, and general nullification is sufficient for it, even le-khatehilah. And although hametz is said to forbid an entire mixture in any amount, these words only apply to an amount which can be seen, and is related to whether one can eat such a mixture on Pesah itself. It is not discussing a mixture in which hametz was nullified before such a time as it becomes forbidden, but after it becomes nullified in a majority [bitul be-rov] before Pesah it does not return and ‘awaken’ [hozer ve-nei`or] – even le-khatehilah such a mixture is permitted.”
The practical implications of this are astounding. What the Ra`avad is saying is:
[i] Grain that got a little wet due to dripping before Pesah [i.e. the kernels did not soak until they cracked open] may be mixed with other grain to nullify it in a simple majority (and apparently a 1/60 ratio is not required).
[ii] An amount of forbidden hametz that would forbid an entire mixture of food on Pesah is ONLY regarding a perceptible amount (i.e. that can be seen). The invisible “blios” of hametz apparently do not count! This means that worrying about supposed “traces” of hametz – not visible to the eye – is not necessary according to the Ra`avad, and it would explain the ruling of the Beit Yosef that cooking on Pesah using a hametz pot that is eino ben yomo does not cause the food to become forbidden bedi`avad (OH 447).
When I read this approach, I was so impressed by how reasonable it was in comparison to the contemporary approach that is something similar to a compulsive disorder.
I also thought that perhaps when the Rambam mentions that hametz forbids a mixture in any amount (i.e. his afilu ba-elef, etc.), they are also speaking about perceptible amounts of hametz like the Ra`avad. This may very well have been the way that the Ra`avad read the Rambam as well since in his hasaghot he makes no comment on this point in the Mishneh Torah nor does he argue with the codification of the Rambam – a fact that usually indicates agreement.
THE SHEILTOT, RABBENU TAM, AND THE RI’AZ
Another interesting and very important statement that I came across recently is that according to the Sheiltot De-Rav Ahai Gaon (Parashat Tzav 3:80) – and subsequently Rabbenu Tam (cf. b.Pesahim 30a) and the Ri’az – hold that even during Pesah hametz may be nullified in 1/60th like all other forbidden substances.