Shot time vs pressure?

[Jigoku]

Ive always worked on the assumption that an espresso shot is 30mL of coffee extracted in ~30 seconds under pressure. I have never really given any thought to the "under pressure" part of that until I found that it is traditionally 9 bar. This got me thinking that the shot times in my 17 bar Gaggia Classic should logically(?) be extracted in a shorter period of time and my fiddling around trying to draw out a 30 second shot time wasnt necessary.

Is this the case? Or is my "espresso" shot awfully under extracted?

Cheers.

[Thundergod]

Re: Shot time vs pressure?

What makes you think the shot is being expressed at 17 bar?

I think youll find that 17 is the maximum rating of the pump.

Most advertisers spew forth about their 15 bar pumps, but lately Ive seen a few "my pump is bigger than yours" ads where 17 is quoted to the gullible public (present company excepted of course).

[roknee]

Re: Shot time vs pressure?

gday
youre on the right track, let me try to help a little.
17 bar is a marketing gimmick - i doubt your machine will reach higher than say 12 bar pressure max in normal circumstances. 9 bar bressure seems to produce pretty much the right amount of pressure to extract coffee well. much more pressure makes life difficult in terms of producing reasonable coffee.

ive only briefly played with the classic, but folks here can get some fairly nice coffee out of it. it may require some tinkering inside the machine to adjust the OPV which basically limits the brew pressure. i think quite often machines like yours are not set to a max pressure of 9 bar our of the factory, so a bit of searching round here and google and youtube will help you out if youre adventurous, and have the will

most folks round here use double filter baskets as the single basket can be hard to use. so the rule then becomes ~60mls in ~30secs.

thats a pretty good guide to get you started. changing the grind of the coffee, the amount of coffee in the filter basket (dose), an even distribution of coffee in the portafilter (handle) and tamping will all affect the end result.


a burr grinder which allows you to make small adjustments to the coarseness of the grind and fresh coffee will probably help the cause too

[Jigoku]

Re: Shot time vs pressure?

Most advertisers spew forth about their 15 bar pumps, but lately Ive seen a few "my pump is bigger than yours" ads where 17 is quoted to the gullible public (present company excepted of course).

Oh lets not start making assumptions that Im not gullible (=

You are right in that the machine is listed as having a maximum pump pressure of 17 bar, with absolutely no indication of what the actual working pressure is ...

gday
youre on the right track, let me try to help a little.
17 bar is a marketing gimmick - i doubt your machine will reach higher than say 12 bar pressure max in normal circumstances. 9 bar bressure seems to produce pretty much the right amount of pressure to extract coffee well. much more pressure makes life difficult in terms of producing reasonable coffee.

ive only briefly played with the classic, but folks here can get some fairly nice coffee out of it. it may require some tinkering inside the machine to adjust the OPV which basically limits the brew pressure. i think quite often machines like yours are not set to a max pressure of 9 bar our of the factory, so a bit of searching round here and google and youtube will help you out if youre adventurous, and have the will

most folks round here use double filter baskets as the single basket can be hard to use. so the rule then becomes ~60mls in ~30secs.

thats a pretty good guide to get you started. changing the grind of the coffee, the amount of coffee in the filter basket (dose), an even distribution of coffee in the portafilter (handle) and tamping will all affect the end result.


a burr grinder which allows you to make small adjustments to the  coarseness of the grind and fresh coffee will probably help the cause too

I know the grind may not fine enough already (Breville BarAroma BCG450 on finest setting without modification) but I wanted to check the effect of pressure before worrying too much about that. Im not sure if it means anything but using an empty double filter basket, the flow through to the cup was about 290mL/30sec. I suspect this is a different flow rate than achieved by measuring back flow against a blind filter (which I found should be approx. 100mL/30s)