This is a word we have borrowed from the corporate world. Commonly used when the news is unlikely to be good but no one really wants to talk about it, as in "there is a lack of transparency over the robustness of the economy for Q4 08".
We think the blending of coffee beans also suffers from a lack of transparency. The accepted wisdom is the divine knowledge of the roaster will produce a blend that results in the perfectly balanced cup of coffee.
Blending also offers the roaster the opportunity to create a little bit of 'intellectual property' if you like. The composition of the blend is not usually declared, and therefore if the consumer responds well to the blend the roaster has a product that is difficult for his competitors to replicate. Fair enough.
The most humourous occasion when the virtues of blending were extolled was in a London restaurant where the waiter tried to convince us that some 30 different beans went into the particular blend of coffee that they served. We are happy to admit that it was very good coffee, but we doubt that anything like 30 different beans had made their way into the blend.
In our experience it is fairly difficult to detect the presence of a bean when it is less than about 10% of a blend. If you assume that the 30 different types of beans were not present in equal proportions, then some of the beans must have been present in concentrations of less than 3%. The presence of any bean at the 3% level or less would not be detectable in the mouth, so it seems highly unlikely that you would bother with anything like 30 beans in a blend.
Anyway, the point of the story is to illustrate the lack of transparency that cloaks the blending of coffee.
But there is a second reason why we have an issue with blending:
Assume you have been told exactly what beans make up a blend, and in what proportions.
Different beans are of different densities. This means that any blend of whole beans is going to settle out or stratify fairly quickly, i.e. when you tip the beans into the hopper of your grinder they will mostly be the beans with the lowest density. This means that unless you ground the entire bag in one hit, then stirred up the resulting ground coffee, that coffee you tasted would differ from what the blender had intended you to taste.
All a bit pedantic I hear you shout?
Well, perhaps, but I think it illustrates why we are skeptical about blending.
Our suggestion is that you buy single origin beans and blend yourself, if you want to go down that path. In this way you have the ability to control the proportions of the blend exactly. For example, weigh 5g of beans A & B, 10g of bean C, and 15g of bean D.
In this way you have complete transparency of knowing what you are paying for, and the ability to replicate your results exactly, time after time, when you strike upon a blend that you particularly enjoy.