maze400 wrote:I thought the crema was influenced more by tamp pressure or grams of coffee used?

Maze400, I've found, both with my old SBux Barista machine and the newer Gaggia Factory lever, that tamp has an effect, but less than I used to be "SURE" of... I've gone from overdosing to 16-17g and a fairly hard tamp (on the Barista pump machine) to 13.5-14g and a light (i.e. 20 lbs or so, with the so meaning less pressure) and getting enormous crema (but the Barista does have, at least part of it's, "crema enhancer" left in place) dark, rich and wonderful tasting. The Gaggia lever.... 11.5-12.2g, light tamp and, while less than the Barista, still wonderful crema... The crema from the Gaggia actually is better, at least visually (and actually tasting as well!)... Not as copious, but very nice... starts out dark reddish and finishes slightly blond (just a drop or two right at the end of the pull).. Nice rich color with tiger striping and great mouthfeel. Some blends make for somewhat darker crema in my experience, but, once I get the grind right, I haven't had a single pull that didn't have nice looking and tasting crema... The pulls for my daily Americano even persist thru the pour into the tumbler that I use to take them to work!

This is ONLY my experiences (and I'm STILL learning EVERY day!)...

I can attest that brew temp has a huge effect on crema colour. I was getting a very dark "crusty" crema for a while, and the coffee itself was a bit too crisp and almost over-extracted. I ended up dialing my PID down 2°C, which made the crema a more golden brown colour and smoothed out the flavour. 2-3° below that and I get a pale yellow crema.

For me, the actual texture and base colour of the crema seems to be more based on the blend of the beans. I have a few exotic blends that come out a very reddish earthy brown with lots of specking, like a 5 day old Maria's Moka Khadir (or Puro Scuro, to a lesser degree), and others that produce the quintessential golden brown with light streaks, like Black Cat.

Beyond that, it's all a mystery to me I just aim for an ideal looking extraction, crema colour, body and quality, few or no bubbles in the surface and taste, above all.

maze400 wrote:I thought the crema was influenced more by tamp pressure or grams of coffee used?

That wouldn't even make sense.

If the coffee is stale, it doesn't matter how hard you tamp or how much coffee you stuff into the basket. The crema will be pitiful at best.

My experiences have indicated that the color of the coffee itself is a better determining factor to the color of the crema than anything else.

The more coffee you cram in a basket, the more volume you can pull before the shot goes blond (within reason) but if you start with bad coffee, you won't get anywhere.

King Seven wrote:I just don't see the science behind this claim - that somehow a stable temperature changes the colour of the coffee liquid to a more reddish hue. I've heard it many times, and obviously read it in Schomer's writings.

In truth I could make no claims for the stability of this machine (I just haven't tested it) but is this red enough for you?

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My new desktop background!

cannonfodder wrote:I wonder how much a plane ticket to London is.

+1...that picture made my mouth water a bit!

As for the original post topic, it is the best and most explained here: http://www.sweetmarias.com/espresso-crema.php.
And a beautiful shot of my espresso from yesterday:

(originally posted on twitpic: http://twitpic.com/32a1pw)

That looks to be from your Peppina or Caravel right?

cannonfodder wrote:In retrospect, I find that the color of the crema is influenced more by the blend contents than machine temperature. For a sure fire brick red crema pull some SO shots with Yemen.

Dave, Can you steer me toward this SO Yemen? I am dying to get that color RED!!! Thanks, Bob

I'm not convinced that crema is just coffee froth containing CO2. I reckon that there is also a process where some of the higher-fat extraction rises to the surface.