This is a straight out description of a blend that I developed for a local commercial roaster, with slight alterations to beans etc. but exactly the same technique.
The first thing to consider about a blend is its purpose. Will it be used primarily for milk drinks, or for black coffees? In this case the brief was to develop a blend primarily for straight espressos and “long blacks”, which was sweet, low acid, full bodied and had a pronounced “chocolate” aftertaste. And of course, being a “commercial” blend, it had to be relatively cheap.
Cheap, sweet and low acid in espresso pointed directly to dry-processed Brazilian coffees as a starting point. Several of these coffees from various plantations were roasted just to the beginning of 2nd crack and cupped.
(A quick digression here; I use a 3 stage process of cupping for espresso, “normal” cupping followed by tasting of a 60 ml double shot followed by tasting of a 60 ml double shot diluted with an additional 120ml of water.)
In terms of sweetness, lack of acidity and reasonable body it was soon clear that Brazils from the Cerrado region outshone those from the Santos areas. In particular the Santos coffees seemed to have a faint undertone of “Iron” on the middle palate and a harsher finish than the Cerrados.
Next came the selection of a bean to add body (mouthfeel) to the blend. This is mostly related to lipid (oil) content, and a neutral robusta would be a possibility, but for Australian purposes a Sumatran coffee would do the same thing. A Java (Jampit or Kayumas) would also serve. The Sumatra Mandheling in particular will also reinforce a “chocolatey” aftertaste, so it becomes a good match.
Finally, for REAL chocolate in the aftertaste, nothing beats an African/Arabian coffee. These are quite hard to get in Australia, the most common ones being the various Ethiopian coffees. In order of cup quality I’d rate the Ethiopians from the best down as Yirgacheffe, Sidamo, Harar, Limu and Djimma. The exotically flavoured dry processed Harar is usually fairly available, and can add complexity and breadth to a blend in fairly small quantities.
Note that at this point of the selection process the choice of beans had been narrowed down to 3 (or 4 if there was a good, cheap, neutral robusta available.) The robusta was ruled out, as the only ones my customer had in stock were extremely heavy on the burnt rubber aftertaste, along with several other less attractive flavours. After cupping one of them, the most printable comment was “Eeyuck! Tastes like it’s been strained through a camel driver’s loincloth!”
Next time you see a long row of blends at your favourite cafe, remember how much effort goes into each one.
Since the person making the comment had purchased a couple of tonnes of this robusta (and had, I assumed, more experience with camel drivers than me) I could only agree.
Now it came down to the grunt work of tasting and spitting. First each of the three beans was roasted to three different end points, just before second crack, 10 seconds after, and 20 seconds after. They were then pulled as individual espressos and tasted, looking for maximising the qualities we were after. In my experience this type of tasting is easier with the diluted espresso, the palate tends to be overwhelmed by the concentrated flavours in a straight espresso and comparison between two is very difficult.
This established the correct “roast points” for the 3 coffees, and all that was left was working out the right proportions of each. All. Hah! This was actually the hardest part. Working with diluted espressos, pipettes and measuring cylinders we narrowed our blend down to:
Each at its own roast point. (And NO, I’m not going to tell you the precise points!) Then we blended from our roasted beans, ground and pulled our first espresso. Was it perfect? No, but it was close. The Mocha in particular seemed to be having less of an effect than we’d counted on, so we backed off a couple of percent on Brazil and pushed it up a bit. Finally we were close to our goal. We now had a “post roast” blend with the right taste.
Again we went back to the grunt work, in order to get a PRE-roast blend (i.e. with the coffees blended green) with this flavour. That’s a whole story in itself, because it involves playing with roast profiles as well as adjusting the bean ratios so that they all roast more or less evenly, but finally we got there. The coffee is now out in the market and selling well.
That’s really all there is to it. Successful blending involves having a clear goal to aim at, reasonable coffee knowledge and tasting skills and heaps of hard, repetitious, boring work.