Question: We forgot to check our eggs while baking a cake, and found a blood spot in the mixture. We removed the blood and baked the cake. Can we eat it? Do we need to kasher our dish?
Answer: The Gemara (Chulin 64b) writes that one mustn’t eat an egg with a blood spot as we are concerned that it is the beginning of an embryo. The Rema (YD 66:8) writes that as the majority of eggs don’t have blood spots, one doesn’t need to check them. Nonetheless, he writes, it is the minhag to check them. One may eat them if they weren’t checked, however (Aruch Hashulchan YD 66:32).
As modern commercial eggs are produced through artificially stimulated hormones, they cannot develop into chickens. Thus, the poskim write that any blood found in them isn’t proper blood. While the Shach (YD 66:14) allows one to eat such eggs even with blood spots, R’ Moshe Feinstein (Igros Moshe YD 1:36; OC 3:61) writes that we should still abide by this minhag and throw out any eggs with blood spots particularly as eggs are so cheap. R’ Ovadia Yosef (Yechave Daas 3:57), writes, however, that in Israel where eggs are more valued, one only needs to dispose of the actual blood spot (See Teshuvos Vehanhagos 1:821; 2:384).R’ Moshe Feinstein writes that if one did bake with eggs which had blood spots, the food would still be considered kosher and the dishes would not require kashering.