It is simple physics BUT often miss understood.Originally Posted by 607276707C4C66607661130 link=1270604790/0#0 date=1270604790
There are of course so many variables. that there is no single response that is 100% correct.
1: Coffee needs to be compressed to a value defined by and wrt the grind size and bean type; to attempt to manage the flow of water at the correct temp at the desired rate.
Outcome = A good cup if ya get it right.
How is the water flow managed = Pump / Tamp / Basket type (single / double floor)
2: Coffee expands when wet -
is it an instant even expansion = NO
pre-infusion has an effect = YES
Temp has an effect = yes
3: If packed to low and water through teh shower screen fast etc then the top layer can get all mucky.
Does this affect teh cup = Yes and no BUT has a major impact on cleaning and dumping the used grinds.
4: If packed right... The beans swell and by the end of teh run, are firm / touching the shower screen and will leave a slight impression in the puck and should be reasonable dry..
With the expansion of the beans.. It also means the level of compactness changes.
So if ya needed x to get a great shot. You would tamp at X + Y where Y = the losses due to expansion.
There are other factors here as to impacting on how it dries etc... As stated before lots of variables and physics taking place.
5: If ya Updose.....
Then in addition to ya tamp; slight pressure is now being applied by the shower screen.
Thus in effect having an impact on that value of Y. Further more as teh coffee has no where to expand it in effect adds to the compression. An inverse reaction.
6: If ya OVERDOSE...
Then ya start to really complicate matters and the pressures involved with expansion etc and water flow realy get interesting.
Thus some people grind courser and compensate by OVERDOSING..
What does this do... Basic logic sates that if you apply excessive pressure to any thing.. Sooner or later things will suffer from stress.
As per shower screens... Meant to diffuse teh water flow to provide an even wetness and path way. When ya always OVERDOSING.. They will suffer over time. But what is really interesting is the excess amount of Oils and gunk that gets forced back-into the system.
So what the trick...
Grind / Tamp and dose correctly and OVERDOSING is NOT required.
Any mathematicians here ? Would make a great formula and then some one can do coffee by numbers; excluding beans type / freshness / grind consistency and any number of other variables that come into play.
Coffee is so simple is it not ;)
Thats why Autos can not pull those great shots day in and day out.. Many of the variables such as tamp and dose can be managed... But the variables are always there :o