MISHNA: This mishna discusses the blessings recited over various foods. How does one recite a blessing over fruits?... GEMARA: Concerning the fundamental basis for blessings, the Gemara asks: From where are these matters, the obligation to recite a blessing before eating, derived? The Gemara answers: As the Sages taught in the Sifra: With regard to saplings, it is stated that in their fourth year their fruit will be: “sanctified for praises before the Lord” (Leviticus 19:24). This verse teaches that they require praise of God in the form of a blessing both beforehand and thereafter, as the verse says praises in the plural. (Rashi: This is referring to the prohibition of eating produce until the fourth year of its planting, and from the plural of "praises" we learn that he requires two praises of the food when he is allowed to eat the produce in the fourth year) From here, Rabbi Akiva said: A person is forbidden to taste anything before he recites a blessing, as without reciting praise over food, it has the status of a consecrated item, from which one is forbidden to derive pleasure... (Brings disproof of the source being the verse) The Gemara answers this: This is not difficult, as it may be derived by means of an a fortiori inference: If when he is satiated, after eating, he is obligated to recite a blessing over food, when he is hungry, before eating, all the more so that he is obligated to recite a blessing over food ... (Brings disproof of source being an a fortiori inference) Rather, all previous attempts at deriving this halakha are rejected. The fundamental obligation to recite a blessing over food is founded on reason: One is forbidden to derive benefit from this world without a blessing. The Sages taught in a Tosefta: One is forbidden to derive benefit from this world, which is the property of God, without reciting a blessing beforehand. And anyone who derives benefit from this world without a blessing, it is as if he is guilty of misuse of a consecrated object... Rabbi Levi expressed this concept differently. Rabbi Levi raised a contradiction: It is written: “The earth and all it contains is the Lord’s,” and it is written elsewhere: “The heavens are the Lord’s and the earth He has given over to mankind” (Psalms 115:16). There is clearly a contradiction with regard to whom the earth belongs. He himself resolves the contradiction: This is not difficult. Here, the verse that says that the earth is the Lord’s refers to the situation before a blessing is recited, and here, where it says that He gave the earth to mankind refers to after a blessing is recited.

The Sages taught in a Tosefta: From where is it derived that Grace after Meals is from the Torah? As it is stated: “And you shall eat and be satisfied, and you shall bless the Lord, your God, for the good land that He has given you” (Deuteronomy 8:10). I only have a Torah source for blessings after eating, i.e., Grace after Meals. From where is it derived that one is obligated to recite blessings before eating? You said that it can be derived through an a fortiori inference: When one is satisfied, he is obligated to recite a blessing and thank God for food; when he is hungry, all the more so that he should recite a blessing to offer thanks for the food he will eat. Rabbi Yehuda HaNasi says: It is not necessary to interpret the verse this way; rather, it should be understood in a slightly different manner, as follows: “And you shall eat and be satisfied, and you shall bless,” that is the blessing of: Who feeds all;... However, I only have a Torah source for blessings after eating, i.e., Grace after Meals. From where is it derived that one is obligated to recite blessings before eating? The verse states: That he gave you. A blessing must be recited over food from the moment that God gave it to you, not only afterward. Rabbi Yitzḥak says: That source for the obligation to recite a blessing beforehand is not necessary, as it says: “And He will bless your bread and your water” (Exodus 23:25); do not read: And He will bless [uveirakh], rather: And you will bless [uvareikh]. And when is it called bread? Before it is eaten. Rabbi Natan says: That source for the obligation to recite a blessing beforehand is not necessary, as it says when the maidens told Saul: “As soon you come into the city, find him right away, before he goes up to the high place to eat; for the people will not eat until he comes, because he will bless the sacrifice; and afterwards all those who are invited will eat; now go, for you shall find him at this time of day” (I Samuel 9:13). A blessing recited prior to eating is explicitly mentioned in that verse.

MISHNA: Ezra the Scribe decreed that one who is ritually impure because of a seminal emission may not engage in matters of Torah until he has immersed in a ritual bath and purified himself. Regarding this, the mishna says: If the time for the recitation of Shema arrived and one is impure due to a seminal emission, he may contemplate Shema in his heart, but neither recites the blessings preceding Shema, nor the blessings following it. Over food which, after partaking, one is obligated by Torah law to recite a blessing, one recites a blessing afterward, but one does not recite a blessing beforehand, because the blessing recited prior to eating is a requirement by rabbinic law. And in all of these instances Rabbi Yehuda says: He recites a blessing beforehand and thereafter in both the case of Shema and in the case of food.

But don't make a Bracha beforehand- because it is not of biblical origin

Rav Yehuda said: From where is the mitzva by Torah law to recite Grace after Meals, derived? As it is stated: “And you shall eat and be satisfied and bless the Lord your God” (Deuteronomy 8:10). And from where is the mitzva by Torah law to recite the blessing over the Torah before it is read, derived? As it is stated: “When I proclaim the Lord’s name, give glory to our God” (Deuteronomy 32:3), meaning that before one proclaims the Lord’s name by reading the Torah, he must give glory to God... And: The blessing before partaking of food from the blessing over the Torah by means of an a fortiori inference: Torah, which requires no blessing afterward by Torah law, requires a blessing beforehand; food, which requires a blessing afterward, is it not right that it requires a blessing beforehand? The Gemara notes: The logic of this a fortiori inference can be refuted: What is true with regard to food, where one derives pleasure from eating, is not true with regard to matters which offer no bodily pleasure. Therefore, the blessing over the Torah cannot be derived from the blessing over food. And similarly: What is true with regard to Torah, that provides eternal life to those who engage in its study, is not true with regard to matters that do not provide eternal life. Therefore, the blessing before partaking of food cannot be derived from the blessing over the Torah. Furthermore, we learned in the mishna: Over food, one who is impure due to a seminal emission recites a blessing afterward, but does not recite a blessing beforehand because it is of rabbinic origin. The mishna does not derive the blessing recited before a meal from the blessing recited over Torah. Consequently, this is a conclusive refutation of Rabbi Yoḥanan’s statement.

When the gemara on 35a claims that the source for the bracha is an a fortiori, this is not a genuine a fortiori, because if it was, the Bracha before eating would be a Torah obligation. Yet in the Gemara pertaining to one who experiences a seminal emission of Brachot 20, it is clear that it is not.

There is a Tanaitic argument here regarding the blessing before eating bread. In Brachot 48b, all the rabbis there hold that it is a Torah obligation, and the law is like none of them. Rather, the law is like the rabbis in the conclusion of 21a: blessings before food are Rabbanically mandated as we see regarding an individual who had a seminal emission, we make a blessing after but not before, that is to say, that the one after is a Torah obligation and the blessing before is of rabbinic origin

All Brachot if you are unsure whether you already recited them or not, you should not repeat the Bracha except for the blessing on bread of eating because it is of Torah origin

[The following rules apply to] a person who ate and forgot to recite grace (after eating):
If a person forgets and is unsure whether he recited grace or not, he must return and recite grace, provided his food has not become digested.

With regard to all these blessings (before eating), if a doubt arises whether one recited the blessing or not, one should not repeat the blessing,

Rav Alfas rules that now that the Gemara does not resolve the question (of what happens when you begin a Bracha intending to consume one food and then finish it intending to eat another), we are lenient, and even if one began thinking he would consume wine, and concluded the Brachah over beer, he fulfilled his obligation. The Ri however, rules stringently, and one has to recite the Bracha all over again.

Rav Yehuda said: If one forgot and put food items in his mouth without reciting a blessing, he moves them to one side of his mouth and recites the blessing.

They raised a dilemma before Rav Ḥisda: One who ate and drank and did not recite a blessing, what is the ruling? Does he return and recite the blessing that he should have recited beforehand before he continues eating or not? In response, Rav Ḥisda said to them an analogy: Should one who ate garlic and the odor on his breath smells return and eat another garlic so that the odor on his breath will smell? That is to say, one must recite a blessing. Should one who committed a transgression and failed to recite a blessing before eating, remedy his situation by continuing to eat without reciting a blessing (Talmidei Rabbeinu Yona)? Ravina said: Therefore, even if one finished his meal, he must return and recite a blessing. He cites a proof, as it was taught in a baraita with regard to the laws of immersion: One who was ritually impure who immersed himself in a ritual bath and emerged, as he emerges he recites: Blessed…Who has made us holy through His mitzvot and has commanded us about ritual immersion. Evidently, in certain cases, one may recite the blessing after completing the act. The Gemara rejects the parallel between the cases: That is not so, as there, in the case of immersion, initially, before he immersed himself, the man was unfit to recite the blessing because he was ritually impure; here, in the case where one did not recite a blessing before eating, initially he was fit to recite the blessing, and since he did not recite the blessing before he ate and he concluded his meal and is, therefore, excluded from reciting the blessing, he is completely excluded and has no way to remedy the situation.

The Raivid holds that the Halacha is according to Ravina (that you make a bracha even after)