I had some interesting results with the Otto in the last two days. On a recent post I stated there was not much difference between different beans. I am revisiting that.
I choked the Otto yesterday using decaffeinated beans. The beans are hard to grind, clog up the grinder and pack harder in the portafilter. The result is that the maximum pressure that the Otto can deliver, 3 ½ bars, is not enough to get through the coffee puck. Steam leaks out the gasket seal, no coffee comes out at all, and there is no steam out of the nozzle either. Removing the portafilter shows dry coffee grounds. This was using the supermarket basket.
Repeating the process with the espresso basket resulted in too rapid a flow of coffee, and no steam pressure. So the coffee was not packed enough for this basket. This demonstrates the extremes either way. I could have changed to the supermarket basket again and tamped lighter or ground coarser.
I then switched back to the usual caffeinated espresso beans, and double tamped this, using the supermarket basket again. This means filling up with coffee grounds to about 2/3 of what I normally use, tamp down, fill up with another 1/3 and tamp again till it is at the usual level of 5 mm from the top rim of the basket.
The result was for the first time, I got proper crema coming out, just like the DVD presentation, and great steam pressure. So what does this demonstrate?
There must be a continuum of results. On the one end, if the back pressure created from variable of the basket used, bean used, how finely it is ground and tamped is not enough, you end up with coffee and no steam pressure.
If the back pressure is too great you get no coffee at all and no steam. Somewhere in between there is a sweet spot that starts with good espresso and good steam pressure, and progresses to crema, and then to choking altogether with increasing back pressure. The sweet spot zone is probably fairly narrow, and may be difficult to hit consistently.
Another web site who reviewed the Otto commented on this also. It is easier to get consistent crema with a well constructed higher pressure machine, but then you are looking at more serious money, and weight.
Crema is not everything though, as department store cappuccino makers consistently create crema, but the espresso still has a bad taste. To throw more controversy into crema, you can do a search on James Hoffman of the Coffee Collective who stated crema was rubbish and should be skimmed off. But I digress.
Probably the best way of using the Otto is to find the coffee bean mix you like the best, experiment with the grind, basket and tamp pressure until you found the particular sweet spot for those variables, and stick with it.