479. When Not to Recite a Bracha

Brachos 1:19

If a person eats forbidden food, he should not recite a bracha, neither before nor after. Therefore, if one eats tevel (untithed produce) - even food that is only considered tevel under rabbinic law - first tithe from which terumah was not taken, or second tithe or sanctified foods that were not redeemed, one should not recite a bracha. It goes without saying that one should not recite a bracha if he ate meat from an animal that was not properly slaughtered or that died, or if he drank wine that had been used in the service of idolatry.

Brachos 1:20

If a person ate demai (food that was doubtfully tithed) - even though it is only fit for the needy - first tithe from which terumas maaser was taken even though the proper volume of terumah was not, or second tithe or sanctified food that was redeemed but the additional fifth was not added to it, one should recite a bracha both before and after. The same is true in comparable situations.