I put some chicken/beef into my slow-cooker, pour some olive oil and cook it for 4-5 hours. After that, if some meat is still left in the cooker, I may heat it up again the next day or the day after the next day, etc. Then, when all meat is finished, I just throw away the oil & meat juices from the cooker but don't wash the cooker with water. I put new raw meat, pour some fresh olive oil and repeat again the cooking process. Is it bad that some residues of the old olive oil from the previous cookings are present in my new cookings? Is there carcinogenic stuff in the old oil?