Yes, it is surprising. It is also very dependent on flow rate. The shapes of the curves change dramatically if, instead of pulling a shot at a flow rate of around 2-3 ml per second, you allow water to run freely through the group (e.g. flushing). Many people draw poor conclusions about shot temperature and temperature stability by measuring water flushed from the group without significant restriction. The amount of "contact time" between the water and the group, I believe, makes a big difference in the temperature of water coming out of the group.atao wrote:I'm a bit surprised that during the shot that water existing the boiler doesn't fall in temperature due to the influx of cold reservoir water.
I think so.atao wrote:On a related note, do most pump machines push water in the grouphead by also pushing (cold) reservoir water into the brew boiler? Seems fundamentally like it'd affect the shot temp.
Others have concluded that the standpipe inside the Silvia boiler is responsible for preventing much mixing. The theory is that the cold water coming into the boiler, being denser, drops to the bottom. This pushes the hotter water up where it enters the standpipe that leads directly to the group. Sounds like a reasonable explanation to me.