by gscace on Fri Aug 21, 2009 11:29 am AndyS wrote:<image>
Using an ExtractMoJo refractometer, I've been measuring extraction yields with and without engaging my Speedster's manual line-pressure preinfusion.
I think a subtle effect results from the fact that, to maintain a normal flow rate, one grinds a little finer when using an extended preinfusion. The finer grind increases the extraction yield at any given brewing ratio.
Practically, what does that mean? Well, it's all up to the barista. As the extraction yield increases, shots tend to go from sour, to tart, to sweet, to bitter. Or, if one keeps the extraction yield constant, preinfusion allows one to pull a slightly more concentrated shot.
We're not talking huge differences, perhaps a change from 19% yield without manual PI to 20% with PI.
Sometimes it also seems that preinfusion makes the flavors in the shot less distinct. It may be "smooth," but not as interesting.
Meanwhile, I don't think the "forgiveness factor" is relevant with the Speedster, since its spring-loaded preinfusion cylinder, along with the Robur's nice grind, are already pretty forgiving.
Dunno if you have your profiling pump attached to your machine, but if not, and if you were interested in a junket to sweltering MD, we cold run some tests here with my 2-group marzocco, robur, profiling pump with preinfusion enabled or not. I think I prolly have one of the must useful platforms for performing some tests on this. Just need some time, instrumentation (ya oughtta be able to find something quantitative) and the proper motivation.
Interested? I bet Eric S would come over.
-Greg
