I carry/make a few blends... it can be very 'easy' or difficult depending on the coffees you have and goals in mind. The most difficult to 'perfect' was a espresso blend... I found the espresso extraction process brought out different flavor profiles that were more difficult to balance. I first start with a goal... what am I trying to create this blend? For example, when I created my 'breakfast' blend called Harmony my goal was to select a balanced coffee with a touch of acidity to wake up the taste buds. My first decision was to select the base coffee so I roasted all of my coffees and brewed a pot of each of the coffees. I decided in this instance my Colombian was the right base - it had a nice balance, a touch of sweetness and a bit acidic. The key was I was looking for a base with acidity - but did not assault the taste buds with super heavy duty acidity. So, I mix started with a 50/50 mix of Colombian/another coffee... Colombian/Brazil, Colombian/Guat, Colombian/Sumatra... etc. Once I find the 'second' coffee that complimented the base - I play with ratios... 25/75, 50/50, 75/25... Sometimes I find two beans is sufficient, often it may be missing sweetness or body, etc. I try and get the first two beans as balanced as possible.. for example say I land on a 50/50 mix. I will brew a pot of 50/50 mix and slowly add the third coffee... 50/50 mix and then say 25% of the mix volume with 3rd coffee. It's literally a ton of trial and error... I bet I make 30-40 blends on average before I am happy with the results. Once I decide on the final mix - I make the decision of I can pre/post roast blend the coffees. I take the ratio I landed on, blend my green coffee to that ratio and roast. Then I compare the two pre/post roast blended cups and decide which is the best - only then does it go into production.
I never use 'filler' beans or beans that I wouldn't sell as a solid single origin drinker. I figure just like any good chef, start with superior products and you end up with a superior product.
I'm strongly in the blend group but that's likely less to do with taste and more to do with the surprise factor. When you're blending good coffee it's hard to screw up.
For my taste in espresso I much prefer blends as it adds complexity in the cup, layered flavors/texture if you will. I've tried quite a few single origins over the years for espresso and find them flat/boring regardless of changes I made. To each his/her own as with most things in life.
I used to post-blend, but I have since learned that my coffee tastes better and is more consistent if pre-blended. It also allows for a better extraction since all beans have the same level of porousness, since they share the same roast degree. Uneven extraction may lead to a cup that is semi sour and semi astringent or burnt.
As for blends, test and taste. Let your customers test as well, people like what they like. Our best blend has a Brazil base of 30%, a Sumatran base of 20% and a mix of Guatemala and Ethiopian depending on season. Our customers live it!
