12 Years a Slave : Reason for Patsey's lashing

I just want to ask what was the reason she got the brutal lashing? Was the white thing in her hand something to eat? I couldn't really understand what had happened????

She went to a property of someone (an acquaintance of Epps) to get soap so she could wash herself. He got jealous in the process and that's when he decided to punish her.

It was established prior that Master Epps was of the belief that Patsy had fallen under the gaze of Master Shaw, and that the reason she was going to his plantations on Sunday was to..uh..canoodle with him. This made him jealous and angry. When Patsy went to Master Shaw's plantation to get soap after Mistress Epps had refused to give her any, Master Epps succumbed to jealousy, and took out his frustration on Patsy. He's a man sick with paranoia and a serious inferiority complex.