Preinfusion pressure profiling on a modified Bezzera Strega

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#1: Post by TomC »

Nicholas's work on pressure profiling in his new awesome thread got the gears in my head turning. I'm no where near his level of know-how or tech skills. But I started thinking I may have overlooked something that I could take from some of his insights and apply them to my modified Strega with a rotary dimmer switch on the vibe pump.

After installing it last winter (with John Borella's patient guidance on how to install it) I began playing with it and seeing the new and incredible capabilities that allowed me to dabble with. You can engage the pump (pull the lever) leave the lever down, and surf around (albeit blindly) varying pressure throughout the entire extraction if one were to want to. You literally don't even need to release the lever if you don't want to. That proved fun, but inconsistent and fiddly. Fun nonetheless, but not my point.

But after getting hooked on the odd revival of old school Italian espresso blends I learned that I can also replicate beautiful classic soft Italian chocolatey and smooth shots by turning the pump nearly completely off and using the Strega as a simple, classic commercial lever. A big long flush, and I was off; getting deliciously rich, buttery deep shots from highly extractable Italian roasts without ashiness or notes of burning tires.

This, plus Nicholas's latest thread had me thinking I might be able extract my espresso with better consistency, plus a wider fudge factor prep wise, and still lead to far better shots. My preliminary simple testing seems to point that it might be something worth further exploration.

Simply stated, on my Strega, with the pump essentially off (it's never completely off, but the flow is so restricted when dialed "off" that it might as well be), my adjustable line pressure provides a very simple, straightforward pre-infusion. Normally, on high acid, light roasts, they need the added punch of high pre-infusion pressure to properly extract anything other than tongue searing battery acid. This is basically the converse of soft, dark Italian roast method of extraction as I noted above.

But if I were to start the shot with the pump "off", very briefly, for about a second after engaging the lever all the way down, then slowly ramp up the pump to near it's max output within about 5 or 6 seconds, I'm left with far better tasting extractions that take much longer to blonde, and pour very, very evenly, even if I was slightly lazy about my distribution or basket prep. I'm thinking this is a clever, very simple way to gradually prepare the puck for extraction without hitting it so suddenly with a full 9 bar pressure "punch". The ramp up the way it is stock might not be sudden or severe, but slowing it down a touch certainly seems to help.

All my shots yesterday and today since I started doing this seem better, richer, the extractions look thicker, taste less edgy, etc. I'm still using the standard pressure declining action of the spring to accomplish the actual extraction, but combining the natural gentle pre-infusion of a "pump-less" commercial lever, with the gradual but quick ramp up on a pre-infusion pressure has seemed to land me in a new espresso nirvana zone. If you have a modified Strega, I suggest you give it a try. If you have a stock Strega (with a pump), I highly suggest you do this simple $8 modification and expand your espresso extraction repertoire.
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#2: Post by Javier »

Great thread!
TomC wrote:If you have a stock Strega (with a pump), I highly suggest you do this simple $8 modification and expand your espresso extraction repertoire.
It would be helpful if either you and/or John Borella will provide a "how to" (with plenty of pictures) for said "simple $8 modification".
LMWDP #115

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#3: Post by TomC (original poster) »

I certainly plan to. It's been on the back burner for a bit too long, but I'll get to it.

The vacuum relief valve reroute drain mod is also discussed in the massive O.E. Strega thread, but I think I took enough photos to walk someone through it.
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#4: Post by JohnB. »

Adding the dimmer pump control gives you lots of options. I pulled several shots today using the 2011 Ethiopia Dara Kebado that I had roasted to City+ for syphon brew. With only a 1:30 stretch after 1C started it wouldn't normally be an ideal choice for espresso. I used a much finer grind setting then normal & dialed in the dimmer for a 1 bar preinfusion pressure as suggested in Nicholas's thread. Once the group had pressurized I lifted the lever just enough to cut off the pump & let the shot proceed at 1 -1.5b until the bottom of the cup was covered. I then engaged the lever retarding its movement until cutting the shot at about the 11:00 position. Total shot time was well over a minute producing about 28-30ml of liquid & crema. The shot was deliciously fruity with a mild acidity & probably would have made a phenomenal Americano.

If you are going to add the dimmer control I'd highly recommend either installing an external pressure gauge or swapping out the stock gauge for a dual pressure gauge. It really is helpful to see what pressure you are actually dialing in as a particular dimmer setting will not always produce the same pressure.


#5: Post by erik82 »

I'd like to see some pictures of how you guys did the mod. I'd like to swap out the standard gauge for a dual gauge and build in a dimmer on my Strega. I already love the machine but this mod should make it so much better. If someone can help me out a bit by posting some pictures I'd appreciate it.

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#6: Post by TomC (original poster) replying to erik82 »

Done. Give me a minute...
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#7: Post by TomC (original poster) »

Ok, it took a bit more than a minute... I'm tired now and I'm going to bed.

Step by step directions for these modifications can now be found here

Please keep this thread on topic of actually using the modifications and how they affect your extractions, tips etc.The build thread will only serve as a tech tip along with updates as I add various other contraptions onto my Strega.
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#8: Post by PeteC68 »

Hi, first time post.

Am considering the dimmer switch mod amongst others. Curious to hear members thoughts about how to install the gauge to measure preinfusion.

Not so much where/how to mount the external gauge (although that would be helpful too! :D ) more important is where in the water systen the gauge would need to be attached and how.

Many thanks for your time, Pete

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#9: Post by okmed »

If you download the Strega pdf file ( ... ng&lang=en ) from the Bezzera website, there are parts diagrams in there. The diagram on page 7 with the flow piping, tags the only "cross tee" fitting #27 and a cap on that tee fitting #30. Remove that cap and attach the gauge to that "cross tee" fitting. If you go to 1st-Line Equipments website ( ... iewAll=yes ) click on Espresso parts then Bezzera and you will find a Bezzera dual gauge ( ... 2p6654.htm ) that you can put in the same opening the single gauge occupies ( check with 1st Line if the diameter is the same ). Then use the pressure gauge capillary ( ... 2p1264.htm ) to connect it to the "cross tee" fitting. This will give you pre-infusion pressure only because the check valve above the "cross tee" will block the extraction pressure. To accurately read extraction pressure throughout the lever stroke you will have to cut in a fitting or adapter some where between the check valve and the lever group body. Please take pictures amd report back if you go through with it. Hope this helped.


#10: Post by PeteC68 »

Okmed, thank you so much for the info. It was exactly what I required. Sadly 1st Line don't ship internationally anymore. Guess I will have to set up a mail forwarding account with someone, to get the parts shipped down to Oz.

Am most interested in the pre-infusion stage, as the pressure with the spring mod may be more trouble than it is worth.

I am also planning on doing the dimmer switch mod as well.

Can't wait to see how the mods affect the espresso results.

Once again thanks to you and those that have provided info on this site.

Will try and get photos if possible and report back how things turn out.
Kind regards,