jpscoffee wrote:Blend - Brazil, Guat, Sumatra
No problems inherent to that sort of blend.
Aging - we are aging our blend at least 8 days because of freshness bubbles
How is the coffee stored during these 8 days? "Days off roast" are not all created equal. The conditions under which that coffee is resting is JUST as important as the number of days. 8 days in air-tight bags with one-way valves is a decent rest for espresso. 8 days NOT sealed in a (basically) air-tight environment is probably too many.
Machine - issue shows up on both our Rancilio Classe 8 and NS Aurelia - Classe 8 set at 1 atmosphere, Aurelia is only about 3 months old machine.
Do you have anything to measure the brew temp? If the temp is too high, it will generally yield less crema than otherwise.
Water - We have full Everpure High Flow CSR Triple-MC part #9328-05 on the water supply and an Everpure filter just before the machines (QL3 head (9272-12) and ESO cartridge (9607-10)). The ESO is a three stage blending cartridge that softens, buffers, and filters.
A big red flag here. The type of filter is irrelevant. The resulting water is what's important (TDS, mineral content, etc.). At the very least, get your water tested for TDS. TDS that's too high will generally yield less crema than otherwise.
Can anyone identify the most common culprits of this problem? Any other facts you might need to diagnose?
How much are you dosing? Dosing too little will generally yield less crema than otherwise.
What kind of baskets are you using? Baskets that are too shallow will generally yield less crema than otherwise
What kind of grinder? A grinder with smaller and/or duller burrs will generally yield less crema than otherwise. Also, a grinder that's HOT will generally yield less crema than otherwise.
How dark is your "dark" roast? A darker roast coffee will generally yield less crema than otherwise.
Technique is going to be critical as well. If your dosing isn't fundamentally sound (leading to channeling or unbalanced extractions), it's gonna hurt the crema.
Hope that helps. Remember though... there isn't a huge correlation between quantity of crema and the taste of the coffee.