cannonfodder wrote:...where does HB think it went blond, including the taste test...?
This extraction was not the first of the day, but the only one I videotaped because I wanted to test the natural lighting. I intentionally let the shot go longer than necessary. The overall time shown in the video is 27 seconds. I just timed it with stopwatch in hand; were it not for the video production, I would have cut it off at ~21 seconds, which corresponds to the tail end of "F":
Stop it here...The taste did suffer as a consequence of continuing past this point. It was still a good espresso, but the extra seconds dulled the flavors and reduced the body. As others above commented, I also use the "collapse of the cone" as a signal:
A "can't miss" sign that the end is near...It is caused by a change in surface tension when the dissolved solids plummets and the higher surface tension of purer water causes the cone to "pucker up". I asked my good friend Bob Barazza, a retired chemist, for a better explanation (paraphrased):
Bob Barraza wrote:[The loss dissolved solids and...] the loss of CO2/crema and emulsified fats are reasons for the increase of surface tension. It is all about the increasing surface tension as you approach pure water. The high surface tension of water is what makes it want to form spheres or droplets (minimum surface area). We add stuff like detergents to reduce the surface tension and allow it to wet flat or rough surfaces.
I voted "F" because of the reduced striping, onset of stream twisting, signs of blonding, and increased translucence of the flow. As a rule of thumb, these signs follow about 5 seconds after the cone collapse. If the same extraction was through a spouted portafilter, the primary signs would be the loss of striping and the onset of translucence prior to the "marking" of the espresso by a lighter dot.