by Tom Owen of Sweet Maria's
In general, the goal of espresso blending differs from the goal of filter coffee blends (and some may argue that there are blends specific for French Press brewing or for serving with cream/milk). Filter coffees may be blended for complexity or for balance, but an espresso blend usually must be blended for balance or particular cultivar qualities that would be favorable in a filter coffee brew might overwhelm the espresso extract.
Most espresso blends are based on one or several high quality Brazil arabicas, some washed, some dry-processed. They often involve some African coffees for winey acidity or enzymatic flowery /fruitiness, or a high grown Central American for a cleaner acidity.
Dry processed coffees are responsible for the attractive crema on the cup, among other mechanical factors in the extraction process. Wet-processed Central Americans add positive aromatic qualities. Robustas, or coffea canephora, are used in cheaper blends to increase body and produce crema and in a few decent blends. They add crema and a particular bite to the cup. The notion that true "continental"espresso blends have Robusta. Nonsense! In fact the coffee samples from small Italian roasters I have (in green form) appear to be very mild, sweet blends with about 40% Brazil Dry-process, 40% Colombian and 20%+ Centrals, like Guatemalan. For bite and earthiness you can use a DP Ethiopian like Sidamo or Djimma. Its fun to play with Robusta but I personally don't like it too much beyond experimentation and I personally don't enjoy having more caffeine in my coffee than is necessary,
A Colombian-based espresso blend offers a sharper, sweeter flavor but won't result in as much crema production. Here are a couple interesting espresso blends we have fooled around with.
Either you can blend by the seat of your pants (not recommended) or make your process of establishing the coffees and the percentages logical. Start by developing the base, the backdrop in terms of flavor and a coffee that provides the kind of body, roast flavor and crema you like. I suggest Brazils, although Colombian or Mexican are viable options.
Practice roasting this base coffee to different degrees of roast, and pulling straight shots of espresso. Get familiar with this cup and imagine what you would like to improve in it (because if you find it just fine as is, then you have no need to continue!)
Do you want it to be sharper and sweeter, with more aromatics: perhaps you will want to add Central American coffees. Watch out with percentages above 25%, particularly if you like a lighter espresso roast. You will be losing some crema and body.
Do you want more body and sweetness: use a clean Indonesian like a Sulawesi or a premium Sumatra. You will be losing some sharpness. You can go up to 50% with one of these ...heck, they are nice at 100%!
Do you want an earthy aggressive bite and more pungency: try a dry-processed Ethiopian. Harar is brighter and more aromatic with fruitiness and ferment. Sidamo has great pungency in the darker roasts, fruitier in the lighter roasts. Djimma is not so fruity and less bright but adds earthiness. These produce great crema. I often enjoy straight shots of these coffees, but keep it to 25% or so in most blends.
Do you want spicy pungency: try a Yemeni coffee. These add ferment too, and great crema. I keep this to 50% or less (normally 25% or so) in blends.
Do you want extreme bite: try an Aged coffee, a Monsooned coffee (Indian or better yet the Sulawesi Rantepao) or Robusta. Aged coffees and Monsooned add certain funky tastes that you will love, or perhaps hate. You just have to give them a try to find out but that is part of the fun. Robusta --- I would not go there unless you have too. I personally do not like the added caffeine they bring. They increase crema, but you also need to keep them below 20% in the blend, I personally never go above 15% with them. The Monsooned Robusta can get up to 25% it seems...
What coffees won't I use in espresso? Kenyas are just too much acid for my purposes. Other East Africans don't make any sense to me either. They are really filter-drip or press-pot coffee to me. Washed Indonesians could certainly be used but they are not adding as much to crema, and they are not going to lend the sweet aromatics of a Central American, so what's the point? Island coffees: Why?
There's a lot of ways to achieve great espresso. Its fun to experiment and I don't know if there is some terminal point where you achieve the perfect trans-subjective espresso. These recommendations reflect my biases, of course.
Here's a great starter blend for a sweeter, cleaner espresso. The absence of North African or Yemeni coffee takes out a little bite from the cup and possibly some lurking fruity ferment flavor. this is, as noted above, a sweet blend used at a street level roasterie/caffe in Rome. They use a Guatemala Antigua for the Central.
I don't think Colombians really pull their weight in a blend (though many people use them as a base or part of their blends), and like using some Sumatra better:
Some sharp sweetness (Central American) hides behind the nutty Brazil flavors and the wonderful Yemeni aromatics. Mandheling adds body and depth. Yemeni coffees are fun for espresso blends, where they can be used like spice to give zest the aromatically or enzymatically flat blends. Roast to Agtron 40 to 35. Good crema production from this blend due to the many dry-processed coffees
Ah, too sweet, too boring. You want something more aggressive, chocolatey? Drop the Centrals:
You can certainly keep going along this route by adding other coffees (monsooned, aged, robusta) to discover what they add and what they subtract from the blend.
Decaf Espresso? Low-caffeine espresso? That is why we stock the Brazil SWP Decaf as a base. Use it as 50% of your blend to cut the caffeine in half, then add your main "character" coffees as usual. If you wanted an all-decaf blend I would do one of these:
See Sweet Maria's for a wide selection of excellent green coffees.