people have been asking me about my comments that, in working with the Mia, i've come to the conclusion that some espresso blends are more suitable than others for use at home - and that some espresso blends are simply not suitable for use with the average home machine. obviously, there are machines for home and machines in homes that are exceptions.
it's actually been a pretty amazing experience - and the conclusion is still a bit shocking in my own mind. i talked a bit with Duane about it yesterday. and with Tony the other day. i still don't have my head wrapped around it, and in no way do i have any concrete solutions or even a real understanding of the situation.
none the less... my current thoughts are that espresso blends that have a narrow range of acceptable brew temp are problematic for most home machines. This is not just due to the whole temp surfing and temp stability issues - it's also due to the temp instability during extraction of a shot. in addition, it seems like blends with a huge number of beans complicate the issue. this seems to be particularly problematic with coffees that are on the light roast side, coffees that require very high brew temp and coffees that require specific brew pressure. finally, there are some specific beans that present their very own complications and problems.
Commercial Espresso Number One -- this requires a very high brew temp (203.5F) and a slightly low pressure (8.5BAR). If pulled at 202F it tastes shockingly sour and astringent and has a very off "wet cardboard" flavour. if pulled at 204F it becomes ashy. given that even top home machines tend to see intra-shot variance of this sort, the odds of getting a shot that doesn't possess at least one of these negatives is very low. it is possible to get good espresso at home from this blend, but it's very, very challenging and luck starts to play a large part.
Commercial Espresso Number Two -- this seems to produce acceptable (though different in flavour) espresso at brew temps ranging from around 198F to around 202F. At the lower end it is quite sweet and fruity and acidic and at the high end it is spicy and chocolatey.
the above also tend to be compounded by sloppy technique. variance of greater than 0.6gram in dose with many espressos produces dramatic changes in extraction. with most - the results are negative.
in playing around with some coffees over the weekend, Tonx, Bronwen and i came up with a example blend that was, in fact, quite tolerant of many of these faults. it performed well at lower temps and at higher temps. it handled sloppy technique as well as can be expected. the keys were that it was only three beans, it had no "finicky" beans and the base was a coffee that was wonderful as a single origin espresso. in addition, the goals (from the start) were to create a fault tolerant blend that tasted "like Illy but better."
i think many roasters are going to need to think about either creating a home espresso blend or suggesting their blend not be used at home.