Blending is done for several reasons.
The target is to make a coffee that is higher in cup quality than any of the ingredients individually.
However, high quality arabica coffee should be able to stand alone; it should have good clean flavor, good acidity, body and aroma.
So a few reasons why coffee is blended in the commercial world might be:
- The use of lower-quality coffee in the blends, eg. washed robusta.
- 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.
- Coffees are also blended to attain consistency from month to month and crop year to year.
- Autonomy to source coffee from various (or the least expensive) sources and attain a consistent flavor.