I came upon, rather by accident, an interesting review article on a web site:

http://www.ncbi.nlm.nih.gov/pmc/article ... e_9220.pdf

It has some interesting fairly recent information.

Thanks for sharing this. Key take-aways:

• Arabica has 2x fats, 1/2 caffeine, 2/3 carbon dioxide vs Robusta
• carbon dioxide is the key to crema
• the higher roasting temp and roasting degree, the more carbon dioxide is available (until reach very dark) -- this is the same for both Arabica and Robusta
• the longer the time between grinding and extraction, the less carbon dioxide remains
• More fat means less foaming (this is also true of milk - skim milk foams more than whole milk)
• In respect of the elements of foaming (FFA and FFB), FFA (foam stability) is tasteless, but FFB (foamability) has intense coffee aroma and bitter taste
• Robusta foam drains more quickly and changes faster to a dry foam that adheres to the glass / leaves a residue, in contrast to Arabica which drains slower and leaves no residue
• Arabica has tiger-tail patterning due to tiny coffee particles trapped in the borders of the foam bubbles; the particles may contribute to foam stability
• foam is most internally consistent at a medium roasting degree
• the higher the water pressure during extraction, the greater foam volume
• higher foam volumes relate to lower foam persistence (though persistence does not relate to roasting degree)
• foam may collapse due to (a) water evaporation leading to thinning of foam films; (b) collapse caused by increased concentration of coffee particles in the thinning foam; (c) high levels of carbon dioxide destabilizing the foam; (d) free fatty acids reducing the strength of the bubbles

A gross simplification for me, is that if you go for the big wow of lots of crema and strong coffee aroma, you're probably getting less fat, more roast, more bitterness and less persistence (unless you count the dry foam that Robusta produces as persistent). You can compensate by grinding just before you brew... although if you have too much CO2 your bubbles are more likely to burst faster anyway.

Except for the bitterness caused by the FFB foaming agent, none of this addresses the effects on taste such as roast degree and amounts of fats or even brewing pressure. I suspect this article will be of great interest to food scientists who are more concerned with determining how they can address the first impression expectations of consumers rather than providing a product that is satisfying at a taste level. To some extent this reflects some of the OCD people get trapped into with espresso porn... they sink dump shots that don't look right even though they may taste great. And they YouTube gorgeous shots that may not taste very good.