After having had a short discussion with R@L on nl.dranken.koffie, I decided to play around with the brewing temperature of my espresso machine. For those who didn't know yet, I added a PID to my espresso machine, so I can set the brewing temperature.
I always brewed at 95.5C (as suggested by David Schomer), this will give a reddish-brown crema. I know a lot of people go for 92C, but I always found the espresso too sour/acidic. If you have read some of my other postings, then you know that this may have been caused by bad roasting in my IMEX. But I have solved this IMEX problem now.
In Italy the official definition of an espresso is 88C!!! Surely that sounds too acidic to me. However, I tried a couple of shots at that temperature, and the result is a very smooth (both in taste and texture), creamy, mild espresso. I can definitely recommend it. The crema will be a bit paler though. I only tried this on a Mexican bean that I bought in February this year from Algerian Coffee Stores.
I also tried this bean at 95.5C and then the taste is more bitter and complex. More comparable to a very good Starbucks shot (if such a thing exists).
So I will definitely play with the brewing temperature a little bit more. Any comments are welcome!