Gemara

(Mishnah): If barley (for the Omer) became wormy, it is Pasul.

(Beraisa): If Soles was mostly wormy, or wheat was mostly wormy, it is Pasul (for Menachos).

Question (R. Yirmeyah): Does this mean that most of each wheat kernel was wormy, or most of the kernels were (at least partially) wormy?

This question is not resolved.

Chulin 67a (Beraisa): "You may eat anything in water" permits bending down to drink from pits.

We are not concerned lest one ingest worms that alighted on the wall of the pit. Since they never left the pit, they are permitted.

Questions (Rav Yosef): If a worm separated and died immediately, or if it entered the air (but never landed on the ground), what is the law?

Questions (Rav Ashi): What is the law if a worm separated to the outside of the date; or to the outside of the date pit, or from one date to another?

These questions are unresolved.

Rishonim

Teshuvas ha'Rosh (20:3): Surely, worms found in salt or flour are forbidden. Who can say that they did not separate, swarm on the ground, and return?!

Terumas ha'Deshen (171): A case occurred in which worms were found in wheat. Even grains that looked whole from the outside, when they were broken, worms were found in many of them. There is no clear solution. However, in pressed circumstances one may select a pile without any grains with holes from the worms. One may not use those with holes, for we must be concerned lest the worms left and returned. Ra'avan, and Avi ha'Ezri citing R. Yo'el, say that we are concerned for this regarding Peros, legumes, beans and lentils. Presumably, the same applies to wheat. Even though some Ge'onim were not concerned for this and permitted, for Torah laws we follow the stringent opinion. Do not say that the stringent opinion is concerned only when the worms are in front of us, but if not, we are not concerned lest there are worms, and they separated and returned. Since there is a problem in front of us, i.e. we saw many, and there were worms in the wheat kernels we broke, surely there are worms here. There is only a single Safek (perhaps they separated and returned). We must be stringent even if we select (and remove the ones with holes). It is very hard to select from a big stack without error. I heard that people are lenient, and rely on a Rav who permitted. He holds that it is not normal for worms to be ground into the flour, for when the wheat is poured into the mill, any worms in wheat with a hole flee and leave through the walls of the Afarcheses (the funnel from which grain descends to the mill), due to the noise and shaking of the Afarcheses. All Nochri grinders say that if flies or mosquitoes fall on the millstone, they are not ground at all; they flee. Even if this is not a sure matter, we need not be stringent, for even if the worms are ground, they are Batel in 60 parts of flour. This is not being Mevatel an Isur l'Chatchilah, since it is a Safek if any Isur will be mixed, and he does not intend for Bitul. Orchos Chayim says similarly. However, one must sift the flour in daylight to see well if any worms, that died from the heat and flour dust of the mill, fell in.

Poskim

Shulchan Aruch (YD 84:5): Worm found in flour or similar things are forbidden. Perhaps they separated, swarmed on the ground, and returned.

Beis Yosef (DH Kasav ha'Rosh): The Agudah (Elu Treifos 72) permits worms found in flour or grain. Menachos 85b connotes like this. If flour or grain is mostly wormy, it is Pasul for Menachos. This implies that it is permitted to people! However, one could reject this. Perhaps it is Pasul for Menachos even if the worms are no longer inside. If they were in the sifter, and returned to the flour, they are forbidden (even to people). Hagahos Sha'arei Dura (52:1) says that he heard from Rivam (Bach - Or Zaru'a) that if flour became wormy in the barrel, even if the worms separated to the wall of the barrel and returned to the flour, they are permitted, just like liquids that became wormy and the worms separated to the walls of the barrel. I say that it is a mistake. Regarding liquids, extra words "mi'Kol Asher ba'Mayim" permit drinking from pits and caves. The Gemara never resolved the law of gnats in chickpeas and mites in lentils that partially separated to the air and returned. Therefore, it is totally forbidden. I heard that a case occurred in which wheat became wormy, and my father commanded to cast it in the river. He did not permit selling to a Nochri, lest the Nochri bake bread and sell it to a Yisrael.

Bach (12): I say that we are concerned only when the mites grew a little, and we see them moving in the barrel, and swarming back and forth. If they are small, and one sees them only through scrutiny in the sun or near a fire, surely they did not separate. There is no concern lest they separated and returned, for this is not common. The Agudah and Sha'arei Dura permit mites that grow in flour when they are small. The Roke'ach (461) distinguishes like this.

Shach (14): The Rosh forbids only small mites, which cannot be sifted out. If big mites are in flour or other foods, the food is permitted, for one can sift out the mites. The Rema (Sa'if 9) says so.

Shach (15): The concern is not only lest they separated and swarmed on the ground. Even if they separated to the inner wall of the Kli and returned, it is forbidden (Sa'if 1). Only regarding liquids, we are lenient when it separated to the inner wall (Sa'if 1), for we learn from "mi'Kol Asher ba'Mayim." This is why the Rema says 'the same applies to other matters that are not liquids.'

Rema: The same applies to salt, or other matters that are not liquids. One may not sell it to a Nochri, lest he sell it to a Yisrael.

Bach (12): One may not sell flour to a Nochri, lest he bake it and sell the bread to a Yisrael, but one may sell wormy salt, legumes or Peros. These often become wormy, so even if the Nochri will sell them to a Yisrael, the Yisrael will check them, and no Isur will result. The Ran says so.

Rebuttal (Taz 9): The Bach learns from Teshuvas ha'Ran (57:8), who concludes 'since they are recognized, and it is known in the city, one may sell them to a Nochri.' Really, the Ran refutes the Bach! He discusses wheat that sprouted, regarding Pesach. There, all can see this, and it was known in the city, therefore he permitted selling to Nochrim. Here, it is common to buy salt, legumes or dry Peros from Nochrim without checking them at all, unless one notices a problem. Therefore, one may sell them to a Nochri only little by little, like we say about wheat that got wet (OC 467:1).

Taz (7): The Yam Shel Shlomo (Chulin 3:125) permits feeding (wormy flour) to one's (Nochri) slave, just one may not keep it a long time, lest one stumble (and a Yisrael eat it). This is like we say about Safek eggs. I disagree. There is concerned for Takalah (stumbling) even in a short time! In YD 86:9, we are not concerned for Takalah in a short time. (If a hen is Safek Tereifah, we wait to see if it will lay all its eggs and become pregnant again, which would show that it is Kosher.) There is different, for the owner refrains, and has nothing to do with it. Therefore, we are not concerned for Takalah. Here, he will make bread. Perhaps it will be mixed with other bread. Since it is eaten in his house, one cannot be careful that it not get mixed.

Taz (9): May one make whiskey from wormy flour? One takes only a Zei'ah (secretion) from the wheat, and it becomes whiskey. There is only taste, but not intact wheat. I say that this is not being Mevatel an Isur, for he intends only to take Zei'ah. However, I forbid for a different reason. We permit selling to a Nochri only a little at a time, lest he sell to a Yisrael. If the Yisrael has any Heter (to use the wormy flour), he might come to eat it intact.

Shulchan Aruch (14): One may grind wormy wheat. He must sift the flour in daylight.

Shach (39): Hagahos Sha'arei Dura says that a case occurred in which wheat became wormy, and his father commanded to cast it in the river. This is brought also in (or in the name of) R. Chaim Kohen, Teshuvas Maimoni, Maharam, Isur v'Heter, Beis Yosef and Torah Chatas. It is difficult to say that Terumas ha'Deshen argues with all of them, and that we rely on him to permit! Rather, the Poskim forbid when most is wormy, and one cannot select the wormy ones. Then surely we do not rely on Terumas ha'Deshen's reasons to be lenient. Even he permitted only when one selects before grinding. Then, it is a mere concern lest worms remain, so we rely on the other reasons. Also the Yam Shel Shlomo (3:125) says that we are lenient only in such a case.

Rema: He discards every worm that he finds, and the rest is permitted.

Taz (20): We permit the rest due to a Sefek-Sefeka (two doubts). Perhaps no worms remained, and even if some remained, perhaps they dissolved at the time of baking. This is not Mevatel Isur l'Chatchilah, for he intends only to bake, and not for Bitul.

Shach (40): Terumas ha'Deshen says that any worms in wheat with a hole flee due to the noise and shaking of the Afarcheses. If so, if a mill has no Afarcheses, e.g. a hand mill, it is forbidden. However, Terumas ha'Deshen permitted also because any worms will be Batel after grinding. IF so, it is permitted in any mill. The Shulchan Aruch connotes like this. However, if one can use a big mill with an Afarcheses, he should do so.

Gra: Orlah (1:6) says that if a tree of Orlah or Kil'ai ha'Kerem was mixed with permitted trees, one may not pick the fruits. If he did, if there are 200 times as much Heter, they are permitted. R. Yosi permits picking with intent for Bitul. Terumos 5:9 says that if Terumah fell into less than 100 parts of Chulin, but the Chulin was superior and after grinding it is more than 100 times the volume of the Terumah, it is permitted. The Yerushalmi brings a Beraisa that permits to grind. It suggested that the Beraisa is like R. Yosi. It concludes that it is even like Chachamim (who argue with him), for it is normal for Kohanim to grind a mixture of Terumah in their house (it is not evident that he intends for Bitul).