To achieve complexity it is necessary to blend for espresso, since a single origin coffee will often lack this quality.
The advantage of espresso over other brewing methods is a result of the Crema. Without Crema the espresso is strong and thick. Aromatic compounds are trapped in an emulsified layer of tiny bubbles (Crema), which coat the tongue and break allowing a lingering aftertaste to be enjoyed after consuming. A well prepared espresso is essential for an aromatic coffee experience.
Espresso blends are made up from a base of coffees eg. Brazil, Dominican Republic, Peru or any origins which have non-overbearing flavour but still contribute sweetness and body.
Colombian , Costa Rican, Guatemala and Venezuela can be used to add acidity, body and flavour. These coffees can often be very acidic, and used in small amounts.
Ethiopian Harrar, Kenyan, Yemen Mocha, Zimbabwe, and Zambian coffees are used to add complexity and brightness.
Sumatra, Sulawesi, Java, East Timor, Papua New Guinea and Ethiopian Yirgacheffe add richness and body.