http://www.unitministry.com/about/coffee.php?pagenum=2 – added this one – see what you think – it’s so subjective we still prefer to add the water after – to judge proportion better – crema disruption not an issue as an espresso from fresh roasted coffee is almost all crema anyway – shape of the cup also has an impact - most important that the barista is in control of how long the water or espresso sits before adding together
http://www.coffeeboard.com.ph/if-beantobrew.htm
http://www.coffeeresearch.org/espresso/tamping.htm
http://www3.interscience.wiley.com/journal/102523068/abstract?CRETRY=1&SRETRY=0