Dear Alan, Thank you for the Aeropress, which I use twice a day. There's nothing else like it. Quick to use, efficient and delicious coffee is the result. My one concern is that I usually find an oily film on the surface of the coffee. When I refilter it through a brown paper filter, the oil disappears. Same thing when I use unbleached filters in the Aeropress instead of the standard white paper filters. Any idea what this oil is? – From Dennis L.

Coffee beans naturally contains oils which float on water. You can see oil on the surface of dark roasted beans. Even light roasted beans contain the same amount of oils, but they haven't been forced to the surface by extended roasting. Paper filters, bleached or not, remove some of the oils and re-filtering removes more oils. The effect on flavor is subtle.