Stolen foods:[1]

The robber: It is forbidden for one to eat a stolen food. It goes without saying that it is forbidden for him to recite a blessing over it, whether a before blessing or an after blessing. This however only applies so long as the food has not changed ownership from the owner to the robber, however if ownership has changed and the food is now considered owned by the robber who is eating it, then although it is still forbidden for him to recite a before blessing[2], nonetheless an after blessing is required to be recited.[3] This applies whether the owner has given up hope of retrieving the food, or the food has gone through a change.[4]

Another person:[5] If the stolen food was given or sold to another person, it remains forbidden for him to eat the food or recite a blessing over it, so long as it remains in the ownership of the original owner from whom the food was stolen. However, if ownership of the food has changed and the food is now considered owned by the person eating it who is not the original robber, then both a before and after blessing is required to be recited.

How does the food change ownership: Food can change ownership from the original owner from whom it was stolen to the possession of the robber, or other individual to whom the robber sold or gave it to, through one of two ways: 1) The owner giving up hope of retrieving the food. 2) The food going through a change. If the owner after discovering that his food was stolen gives up hope of ever retrieving the food, then the food changes ownership from him and enters the possession of whoever now has the food, whether the original robber or a second individual. Likewise, if the food went through a physical change, such as it was ground or cooked or baked, then it changes ownership from him and enters the possession of whoever now has the food, whether the original robber or a second individual.[6] Despite this, the robber himself may never say a before blessing upon eating the stolen food, even if ownership has changed and has now entered his possession, being that he is obligated to return it, or being that it came into his possession through sin. However, once the food is eaten by him, since the food can no longer be returned he is therefore obligated to say an after blessing.

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[1] See Admur 196:2-4 regarding stolen bread and the same applies to any other stolen food; 11:12; Kutzur Achron 11:4; 649:6; Hilchos Geneiva Ugezeila Halacha 6; M”A 196:1; Bach 196 and Shut 1; Beis Yosef 196; Olas Tamid 196:1; Rabbeinu Yona on Yerushalmi Chalah 1:5; Rabbeinu Manoach Brachos 1:19; Tehila Ledavid 196:1

[2] The reason: The robber himself may never say a before blessing upon eating the stolen food, even if ownership has changed and has now entered his possession as a result of Yiush, being that he is obligated to return it to the original owner as part of his mitzvah to return the stolen object and he cannot exempt himself with giving money to the owner. Accordingly, it is found that when he eats the food he’s transgressing a prohibition and therefore may not recite the blessing, as a blessing over a prohibition is not a blessing but a blasphemy. [Admur ibid]

[3] The reason: As once the food is eaten by him it now fully belongs to him in a way that it can no longer be returned and rather he must now pay money to the other in exchange for the food. He is therefore obligated to say an after blessing over the food being that the food was considered his. Now, although the original eating of the food was done in prohibition nonetheless, since after the eating he can exempt himself with money, hence making the food be considered his, therefore his blessing is not considered a blasphemy. [Admur ibid]

[4] 2^nd opinion in Admur 196:3 and conclusion there in parentheses that Safek Brachos Lihakel; Beis Yosef 196, brought in M”A ibid

The reason: As it is considered blasphemy to recite a blessing over a food that one retrieved through a sin.

Other opinions: Some Poskim rule that if the food has gone through a change, then the robber is obligated to recite also a before blessing upon eating it. The reason for this is because once the food has gone through a change, it now enters the robbers possession and is no longer than required to returned to the original owner, as the robber can choose to compensate him with money in exchange. Accordingly, his eating is not considered sinful. Now, although we rule regarding mitzvah’s that a blessing may never be said over a stolen object even if it has gone through a change, nonetheless, one cannot compare the laws of blessings over pleasures to the laws of blessings over Mitzvahs. [1^st and Stam opinion in Admur ibid; Maggid Mishneh Chametz 6; Bach ibid; Olas Tamid ibid; M”A ibid; Nehar Shalom 196:1]

[5] Admur 196:4

[6] Admur 196:3 regarding baking stolen wheat or grain into bread