After the first week of testing I had to take a break due to pressure of work. When I resumed, I was getting weird flavours & aromas in the shots, even after rigorous cleaning. Finally I saw that the freshly soaked and rinsed portafilter was still leaking brown goo, from around the black plastic liner. I removed the liner to find an interesting collection of growing things and coffee tars in the base of the portafilter. Thereafter I left the liner out. Sunbeam tell me that it is there to stop heat loss from the coffee to the portafilter, but leaving the portafilter in the group and flushing some hot water through it prior to a shot will prevent this anyway.