Gemara

53b (Mishnah): If a Terumah apple was minced and put into a dough and fermented it, it is forbidden.

It does not become proper Chametz, but it does become Chametz Nuksheh.

Pesachim 35a (Reish Lakish): One is not Chayav Kares for a dough kneaded with wine, oil or honey.

(Rav Idi bar Avin) This is because Mei Peiros do not ferment.

36a (Beraisa): During Pesach, one may not knead a dough with wine, oil or honey;

R. Shimon ben Gamliel says, if one did so, one must burn it immediately.

Chachamim say, it may be eaten (if it was baked promptly).

R. Akiva says, I once made a dough for R. Eliezer and R. Yehoshua (during Pesach) with wine, oil and honey, and they did not comment.

Even though one may not knead with them, one may smear the dough after it is arranged into loaves;

This is according to the first Tana

Chachamim say, one may smear only with things with which one may knead.

39b (dVei R. Shila): Vatika (a tart) is permitted.

Question (Beraisa): It is forbidden.

Answer: If it is made with oil and salt it is permitted. If it is made with water and salt it is forbidden.

40a (Abaye): One may not roast two ears of grain together, lest juice leave one and be absorbed in the other, and it will become Chametz.

Objection (Rava): If so, even one should be forbidden, lest juice leave one end and be absorbed in the other end, and it will become Chametz! Rather, both of these are permitted, because Mei Peiros do not ferment.

(Abaye): If grain was parched in a jug in an oven, if the mouth faces down (so juice that exudes will fall out), it is permitted. If the mouth faces up, it is forbidden.

(Rava): In both cases it is permitted. Mei Peiros do not ferment.

40b (Mishnah): One may not put flour into Charoses (a dip containing vinegar - this is not the dip used at the Seder) or mustard. If one did so, he eats it immediately (before it will become Chametz);

R. Meir forbids eating it.

42a (Mishnah): During Pesach, one transgresses for the following: beer of Madai, vinegar of Edom...

Rishonim

Rambam (Hilchos Chametz 5:9): Chachamim said that one must be careful that water not come on grain that he will eat during Pesach, from the time it is harvested.

Hagahos Maimoniyos (8): Rashi says that a Yisrael must supervise the grinding. This is a stringency. One may buy flour and dough of Nochrim! In many places the custom is to remove grains of wheat from which mice ate. Some permit, because it (the saliva of the mice) is like Mei Peros. This is difficult, for a Beraisa (Pesachim 39a) forbids to chew wheat and put on a wound, for it ferments! This shows that saliva is unlike Mei Peros. Presumably, saliva of mice is the same. One cannot be lenient to distinguish without a proof. Also, when later it is kneaded with water, the mice's saliva ferments like Mei Peros mixed with water. The Tur says that one need not be concerned for this at all. It is a remote concern lest a small amount of saliva in a mouse's mouth can ferment hard wheat. The Gemara permits even Lesisa (mixing the grain with water before grinding it), just Ge'onim were stringent about it. Even if there are bitten grains, they are only one in a thousand. They are Batel when the wheat is ground. This is not called Mevatel Isur l'Chatchilah, for he does not intend for Bitul.

Rosh (Pesachim 3:1): The Mishnah forbids beer of Madai and vinegar of Edom when it has water. If not, we hold that Mei Peiros do not ferment. Also the Yerushalmi says so. The Rif rules like R. Akiva that Mei Peiros do not ferment even with water, i.e. if the dough was kneaded with Mei Peros it does not ferment quickly, and one can guard it from Chimutz like a regular dough. If one puts barley in beer or vinegar for a long time, it becomes Chametz if there is water.

Rosh (2:13): R. Tam explains that Mei Peros without water do not ferment. When there is also water, it becomes Chametz quickly. If one kneaded with Mei Peros and water, the Ritz Gei'us rules like Chachamim, that one bakes it immediately. Bahag says that Rabanan at the end of the Beraisa, who forbid smearing with things with which one may not knead, hold like R. Gamliel, that it must be burned immediately. I do not understand. They discuss only l'Chatchilah! R. Gamliel and Chachamim argue about b'Di'eved, and the Halachah follows Chachamim.

Teshuvas ha'Rashba (488): Presumably, we are not concerned for Chimutz of wheat from which mice ate. The Gemara was stringent only about what a person chewed. If not, no wheat is permitted for Pesach, for mice eat from every stack! Even if mice's saliva ferments like human saliva, we see that it does not crack (like Chametz). Even if a person bit a kernel with his teeth, it does not ferment. All the more so we are not concerned for a small amount (that mice ate from) amidst a lot. It cannot come to a Torah Isur. At most it is a Safek mid'Rabanan.

Teshuvas ha'Ran (59): One year, it rained at the time of the harvest. Wheat that cleaved is surely Asur. It is difficult to say that it cleaved due to moisture of the grain itself, which is Mei Peiros, which do not ferment. Experts say that this never happens. Even if it did, it is forbidden according to Rashi and many Meforshim who say that Mei Peros make Chametz Nuksheh. If water mixed in, all agree that it ferments. Therefore, even if they cleaved due to themselves, they will become Chametz immediately when kneaded with water. There is no difference if the water was added before or after the Mei Peros. There is no source to distinguish.

Poskim

Shulchan Aruch (OC 462:2): Mei Peiros with water ferment more quickly than a regular dough. Therefore, one should not knead with them. If he did, he bakes it immediately.

Beis Yosef (DH u'Mah she'Chasav v'Im): This is like Chachamim of R. Gamliel. The Rosh concluded like the Ritz Gei'us, who rules like Chachamim.

Beis Yosef (DH Mei): Rashi explains that Mei Peros are wine and oil, without water. On 36a Rashi says that R. Gamliel holds that wine, oil or honey ferment quickly, and one cannot be careful with them to guard from Chametz. Chachamim permit eating it. They hold that one can guard them from Chametz. The text does not say '(he must eat it) immediately', for once it is baked, it will not become Chametz. In the Rif's text, Chachamim say 'it must be baked immediately.'

Gra (DH Mei): Even Chachamim forbid l'Chatchilah.

Magen Avraham (1): If a little water fell into the dough and it was not baked immediately, it is not clear whether it is forbidden b'Di'eved. The Rosh connotes that a small amount does not forbid. He explains that this is why Kituf does not ferment.

Mishnah Berurah (6): This is whether the water or Mei Peros is the majority. We do not distinguish between whether the water was put first or last.

Mishnah Berurah (7): It can become Chametz in less than the time to walk a Mil (18 minutes).

Mishnah Berurah (8): If one did not bake it immediately, one may not eat it, even if he did not delay 18 minutes. If this will cause a big loss, Eliyahu Rabah is lenient if it was within 18 minutes and we do not see any signs of Chimutz. If this happened b'Shogeg, surely one may rely on this in pressed circumstances, like we say about kneading with warm water (455:3).

Bi'ur Halachah (DH Ein): If the majority is Mei Peros, R. Tam holds that it is only Chametz Nuksheh. The Rambam holds that it is proper Chametz. If the majority is water, all agree that it is proper Chametz.

Bi'ur Halachah (DH Ein): If Mei Peros fell on wheat or flour and dried, some Acharonim forbid to bake it for Matzah, for the water arouses the power of Mei Peros, and it becomes Chametz quickly. Some are lenient. Once they dried, it is not aroused. In pressed circumstances, one may be lenient, for the Mechaber's law is not according to everyone. The Rif and Rambam hold that it does not ferment faster than a regular dough. The Magid Mishneh and R. Mano'ach agreed. Therefore, one may be lenient if it dried.

Kaf ha'Chayim (17): Some permit if Mei Peros fell on wheat and dried, but not if it fell on flour and dried. In pressed circumstances, one may be lenient to bake it immediately, like one who kneaded with Mei Peiros with water.

Bi'ur Halachah (DH Bahem): In the Beraisa, Chachamim forbid Kituf with Mei Peros. R. Chananel and the Rashba rule like them. The Mechaber omitted this, for the Tur says that some permit Kituf after the first night (and the Shulchan Aruch permits even kneading with Mei Peros - PF). Our custom is to be stringent, like the Rema in Sa'if 4.

Shulchan Aruch (3): One may knead with wine, even though it is impossible that a drop of water did not fall in (with the grapes) at the time of harvesting.

Gra (DH v'Af): We permit Vatika with oil and salt, even though salt is from water and ferments (Sa'if 7). Tosfos (54a DH Ein Machmitzin) explains that in Edomi vinegar, barley is soaked in water beforehand. This is unlike the simple reading of the Yerushalmi, which connotes that there is water in the vinegar.

Bi'ur Halachah (DH Ho'il): The Gra holds unlike the Ran, who permits because the water changed form (to salt. It is not due to Bitul.) The Gra does not hold that wine turns the water to wine, for this does not apply to salt in oil. Rather, it is due to Bitul. The Beis Meir agreed.

Rema (4): In these lands, our custom is not to knead with Mei Peros. Even to smear the Matzah with Mei Peros we do only after baking, while they are still warm.