Could you kindly specify the type of basket that you are using? My Strega is arriving next week and I am not sure if a 12gr basket that can be overdosed with 17-18gr is in my portfolio. What about the large LM baskets (>14gr)?

Thank you,
-Malte

Thanks for your info, Jim. I'll see how it goes after getting it at home. PID the group head heater doesn't really mean it's original design would be defeated. If so desire, I could lower the original temperature setting to even lower the brew temperature. I'd just want to get hold of the control on that important brew factor.

Regarding the filter, I'm fine as long as it's using 58mm ones. I can try all the filters that I have on hand to see which one gives the best results. By the way, can you tell me your guess about why finer grounds/higher dose is required for the Strega? I don't quite understand this. Did the initial pump pressure of 10 bar cause the issue? If that's the case, I may adjust the OPV to 9 bar accordingly.

Adjust the pressure based on flavor, not flow rate. It can be counter intuitive - often reducing the pressure increases the flow rate. Weird, huh?

On the strega, I'm sure an optimal pressure would be hard to figure out unless you're doing pump only shots.

I do not know why the Strega has extra punch. It is also a feature of the NS Athena lever machine which uses the conventional Astoria lever with an HX, but not so much on the BZ2006 which uses a sipper group. I suspect it is the added pressure of the preinfusion (1 bar from the boiler versus 3 bar from the line versus 9 bar from the auxiliary pump). This has two effects: extra water in the cylinder, and extra air pressure added to that stored in the spring. I assume all that extra stored force and mass is responsible for the extra punch.

I suspect the initial design of the Strega was similar to the BZ2006 but with a pourover tank, i.e. a sipper group and a low pressure pump to fill the boiler. The added shot quality that comes from hot rodding the group is something the Bezzera people discovered afterwards. The somewhat odd parts layout suggests such a history of revisions. The BZ2006 is a nice conventional lever machine with OK but nothing to write home about shot quality. The NS Athena is better. The Strega is fantastic. I do not know if this sort of initial pressure hot rodding is something that would work for all levers; but it certainly does wonders on the Astoria group.

I use this basket. As with all baskets, how pretty the holes are has no effect on performance. The point is that this basket has the slightly restricted hole pattern found in 12 gram baskets, but the fill depth of extra deep 14 gram baskets. This makes it very useful for machines with unusually high punch.

The punch of a machine (i.e. how fast it forces would force water through standard puck -- if such a thing could be defined) doesn't have a direct relation to pressure. In general, according to Illy, a pump machine has the most punch at 8 to 9 bar, and drops off again at higher pressures. I have found this to be roughly true on machines where I've adjusted the OPV. The issue I'm running into with the Strega is not more punch at some pressure or another, but more punch in lever machines than in pump machines. Such differences exist, but to a lesser extent, among regular pump machines (e.g an E61 group machine will use a finer grind than an LM, everything else being equal). I suspect it has to do with the water path, and the restrictions that occur between the pressure source and the puck. Since the path between the piston on a lever and puck is as short as it can possibly get, this may be the reason lever machines can develop more punch at the same pressure. But please note that this explanation is speculation on my part.

another_jim wrote:The strength of the machine is that the group head heater is deliberately underpowered, getting overheated water from the HX and produces a strongly declining temperature that converts the high acidity to wineyness, while eliminating bitterness. Correcting this "fault" with a PID would eliminate this strength.

Hi Jim, this seems quite new to me, to my past understanding, keeping the brewing temperature as constant as possible during the brew is desirable for making a good shot, but what you telling is the declining temperature profile converts acidic to wineyness. Could you elaborate a bit more on this?

Winyness in coffee tasting means a clearly high acidity that has enough sweetness to make it reminiscent of raisins. It helps if the associated fruit flavors have some complexity or a hint of ferment that imparts an taste akin to a liquor. This type of flavor is usually associated with lighter roasts of East African coffees, although you also get it in Centrals now, possibly due to the adoption of some cutting edge prep practices derived from studying Kenyan and Ethiopian practices (careful sun drying, longer wet ferment times, or dry/semi wet processing, etc).

This flavor was hard to get in espresso, since roasts light enough to have them were very difficult to pull. The Strega makes pulling very light roasts easy, and in addition, gets winey flavors from a wider range of coffees. This is due to both the declining pressure and temperature; I do not think it can work unless one has both at once.

There has never been any foundation to the idea that a flat temperature profile is preferable. It is simply something that can be made more precise and adjustable using simple PID controls than a sloped profile. The same precision on a sloped profile would require a faster controller, a more advanced control algorithm, and better user interface. Presumably, when controls manufacturers start mass producing cheap controls that can do all this, our espresso engineers will be singing the praises of curved profiles.

Until then, a thought: In my many years of pulling shots, I've found that getting the pressure and temperature roughly right, i.e. with haphazard declining profiles, is better than getting it precisely wrong, i.e. perfect straight profiles. The only place I've found high precision to be really important is in dose and grind, not in temperature and pressure.

another_jim wrote:In my many years of pulling shots, I've found that getting the pressure and temperature roughly right, i.e. with haphazard declining profiles, is better than getting it precisely wrong, i.e. perfect straight profiles. The only place I've found high precision to be really important is in dose and grind, not in temperature and pressure.

Jim, as a lever user, thank you for that and for debunking the idea that a flat temperature profile is preferable. I've thought the latter is less likely to bring out nuances of flavor than some variation. In general this gem puts the focus on barista skills that will make more of a difference.

drgary wrote:Jim, as a lever user, thank you for that and for debunking the idea that a flat pressure profile is preferable.

You mean temperature profile?

Jim, thx for your clear explanation. I wish I can develop good sensory skill to notice subtle difference.

allon wrote:You mean temperature profile?

Yes. I'll correct that above.