DaasYochid – Even if the food wan’t nivla until afterwards, the food itself became pagum from the soap.
Sam – Because we can judge pagum by our own eyes. I can’t tell you I know exactly what kind of soap the Rema referred to or what the people his his place and time were okay with tasting, but I can tell you for certain that any food that acquired dishwashing soap flavor is one that normal people don’t want to eat.