Pesachim 40A

תרי חיטי בהדי הדדי, דילמא אזלא חדא ויתבה בציריא דחברתה, ולא סליק להו דיקולא דמיא מארבע רוחתא, ואתי לידי חימוץ.

two wheat grains in boiling water at the same time, lest one move and rest in the slit [tzirya] of the other, thereby preventing the column [dikkula] of boiling water from entering all 4 sides of the grain, and the grain will come to a state of leavening.

ואמר אביי: לא ליחרוך איניש תרי שבלי בהדי הדדי, דילמא נפקי מיא מהאי ובלע אידך, ואתיא לידי חימוץ. אמר ליה רבא: אי הכי, אפילו חדא נמי, דילמא נפיק מהאי רישא ובלע אידך רישא! אלא אמר רבא: מי פירות נינהו, ומי פירות אינן מחמיצין.

And Abaye said: A person may not roast two stalks together, lest water leave one and be absorbed by the other, and it come to be leavened. Rava said to him: If so, one should not even roast one stalk, lest the liquid leave one end of the stalk and be absorbed by its other end. Rather, Rava said: One need not be concerned about this possibility, as it is considered fruit juice, and fruit juice does not leaven grain.

והדר ביה אביי מההיא, דכל אגב מדלייהו לא מחמצי. דאמר אביי: האי חצבא דאבישנא, סחיפא ⁠— שרי, זקיפא ⁠— אסור. רבא אמר: אפילו זקיפא ⁠— נמי שרי, מי פירות נינהו, ומי פירות אינן מחמיצין.

The Talmud adds: And Abaye retracted his opinion with regard to that halakha of stalks, as he maintains that anything that is absorbing liquid will not become leavened unless it is fully soaked in water. As Abaye said: With regard to this jug used for drying the stalks by means of roasting, if it is inverted it is permitted, as the liquid that is discharged from one stalk will not be absorbed by the other stalks. However, if the vessel is upright it is prohibited, as the liquid retained in the vessel might be absorbed by the other stalks and leaven them. Rava said: Even if the jug is upright, it is also permitted. This liquid is considered fruit juice, and fruit juice does not leaven grain.