Blending is done for several reasons. Presumably, the goal is to make a coffee that is higher in cup quality than any of the ingredients individually. But high quality arabica coffee should be able to stand-alone; it should have good clean flavor, good aromatics, body and aftertaste. So one reason coffees are blended in the commercial world might be the use of lower-quality coffee in the blend. Another reason might be to create a proprietary or signature blend that leads consumers to equate a particular coffee profile with a particular brand image; consumers don’t often call Starbucks by the origin names used in the coffee but simply as “a cup of Starbucks” as if the dark carbony roast tastes were somehow exclusive to that brand. Coffees are also blended to attain consistency from month to month and crop year to year. This is done by major brands that do not want to be dependent on any specific origin flavor so they can source coffee from various (or the least expensive) sources to attain a consistent flavor. Such blends generally reduce all the coffees included to the lowest common denominator. But let’s put aside the less-than-noble reasons that coffee is blended and focus on details that concern the quality-oriented roaster.
Before blending any high-quality coffees you should know the flavors of the individual coffees and have some goal for an ideal cup that cannot be attained by a single origin or single degree of roast. It would be a shame to blend a fantastic Estate coffee, after all, you are supposedly trying to attain a cup that exceeds the components and it’s not likely you can do this with top coffees. Given that you have both a reason to a blend and a logical process for doing it, there will be little need for more than say 5 coffees in the blend. Blends with more than 5 coffees Sweet Maria’s considers fanciful, or indulgent.