Espresso is a brewing process that utilizes heat and pressure in order to extract the most concentrated form of coffee on the planet.
By normal coffee I am assuming you are referring to a more common brewing process such as a drip coffee machine. If the standard (suggested) ratio of coffee to water is used in these other brewing methods, you will create coffee that is less concentrated and hence, less strong, than espresso, per milliiter. In other words, comparing the same volume of espresso to the same volume of other brewing methods.
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