Rancilio Rocky grinder is "different" after burr replacement

[spoke]

Hello everyone and thanks for the ever present input so far. This forum has been a valuable source of information, solutions and advice for me.

Here is my problem (I did do a forum search and did not encounter the exact symptoms):

I have a Silvia/Rocky(with the Teflon tape mod) combination and have been enjoying it for 2 (Silvia) - 3 (Rocky) years. I home-roast. Last holiday season I decided it was time to change the Rocky burrs and ordered a set which I changed with no problems. I noticed there was no Rancilio logo on them. I immediately noticed that the grind was faster (expected). I also noticed that the Rocky absolute 0 point changed from -3 to +8. This was expected and anticipated as well. What I was not ready for was a change in my usual setting for espresso grinding. It changed from abs. 0+7 or +8 to abs. 0 +2 or +3. Mind you, the Silvia cannot be choked at +1. I performed the Ulka pump capacity curve measurement and came up with <9 bar (7.7-8.5).

Another change: I use both the Rancilio double portafilter and the La Marzocco double. I used to grind 18 grams for the Rancilio PF and 21 grams for the LM PF. Now, in order to get the same extraction from the Silvia, I have to grind 19+ grams for the R PF and 23 grams for the LM PF. The grind feels the same between my fingers.

Do you have any clues for me please? I would appreciate them.

Thanks,
Nikos

[HB]

What I was not ready for was a change in my usual setting for espresso grinding. It changed from abs. 0+7 or +8 to abs. 0 +2 or +3.

That's mysterious.

It's only a guess, but perhaps the burrs are not OEM and produce a different particle distribution (see Titan Grinder Project: Particle size distributions of ground coffee). If you buy into this explanation, then I posit that your new burrs are generating less fines, which means less particle interlocking and effective resistance. To compensate for the reduction in fines, a finer grind setting and more coffee are required to produce the same extraction time.

Was there also a change in the espresso's taste?

[spoke]

Yes, I do think your explanation HB, is possible. It is something that makes perfect sense, and has crossed my mind: The grind is perfect now; this is what it was supposed to be. Note that I bought the Rocky used, so I have not seen it perform when new. (One thing though: Wouldn't you expect a given weight of perfectly evenly sized grounds to have a bigger volume than the same amount of variably sized grounds? I observe the opposite.)

But +2? Has anyone had a Rocky grind for espresso that close when new? Everything I have read mentions +7 to +10.

The espresso has been wonderful so far, before and after the change.

Thanks for the reply,
Nikos

[HB]

Wouldn't you expect a given weight of perfectly evenly sized grounds to have a bigger volume than the same amount of variably sized grounds? I observe the opposite.

I think the "fluffiness" is related to the extent of compaction that the grounds must endure on their way out of the chute. The size of the particles is so tiny, I can't make meaningful observations about their distribution simply by observation.

But +2? Has anyone had a Rocky grind for espresso that close when new? Everything I have read mentions +7 to +10.

A grind setting of +2 would be possible for coffees that demand exceptionally find grounds like decaf or Robusta, otherwise a setting of +5 to +7 sounds right. Bottom line: "The espresso has been wonderful so far, before and after the change."

[cannonfodder]

You also mention that you home roast. Did you change crops recently? Beans change crop to crop, they also change as they age. As long as the timing is correct and the shots good, I would not worry about it. Those grind index rings are useful when going from one setting to another (say espresso to pres pot and then back again), but pretty much useless when comparing settings from one grinder to the next

[spoke]

Did you change crops recently?

No. I am going between Sweet Maria's Monkey and Puro Scuro, but both have been very similar during the grind. I do go up to +36 for a french press for my wife once every two days.

I do not know, guys, maybe I am thinking about this too hard. I just had a wonderful ristretto at +3. You are right, that is what matters.

I did notice that at +2 and 19 gr this morning I ended up with a ristretto, so I went to +3 to increase the volume six hours later, but ended up with the same amount in the cup. Many variables could be at play here, mostly environmental. And my scale could be playing games with me.

Reality is I am at +2 to +3 and still get excellent espresso. Maybe I should just forget about it.

Anyway, I do appreciate your taking the time to think about this.

Nikos