An espresso blend is an opportunity to combine coffees for a specific result: more body, a particular aroma, a different balance in milk or a workable purchasing cost. The source suggests a base coffee, a possible robusta component and another arabica contribution, but those proportions are starting ideas rather than a formula every blend should follow.
Taste the components individually with a consistent preparation before combining them. Then make small, weighed blends and change one proportion at a time. A coffee that seems restrained alone may play a useful supporting role, while a striking single-origin character can become less distinct when another component dominates. Judge the blend as espresso and in the drinks it is intended to support.
Cost can be calculated as each coffee's unit cost multiplied by its share, with the results added together. Keep units consistent and distinguish green-coffee purchasing cost from finished roasted-coffee cost. Crema is one observable feature, but it cannot establish flavor quality by itself. A useful blend is repeatable, clearly documented and suited to the intended cup, rather than a collection of prestigious origins assembled without a purpose.
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