Can wide particle size distribution cause severe acidity? - Page 2

Grinders are one of the keys to exceptional espresso. Discuss them here.
Tyme (original poster)

#11: Post by Tyme (original poster) »

mikelipino wrote:Here's the mental model I've been playing with
Thanks for your detailed explanation! My issue with that model is that there's no correction for the effect of surface area. Eg, in the first graph with 8% underextracting and 8% overextracting, the too-fine particles get completely overextracted but the too-large particles don't get fully underextracted because water can't fully access all the coffee at the interior of the large particles. It's as if that interior material just doesn't exist because we never taste molecules extracted from it. So while the weight of both fractions is 8%, all the too-fine 8% gets overextracted but maybe only half of the too-coarse stuff (eg, 4%, just making up a number) gets underextracted. This would skew towards bitterness. I don't know how to account for the taste difference between one unit of acidic compounds and one unit of bitter compounds, though.
RapidCoffee wrote:Obvious question: what coffee are you using?
Short answer: many coffees. Long answer: I made a post about my sourness problem here Help: Nothing fixes my super sour espresso if you want more details. I want to know if it's possible that my grinder may be to blame and therefore I should investigate other grinders, or just focus on the other normal variables for solving acidity. I should also mention that I just upgraded to a Rocket Giotto two weeks ago so I'm not using the Gaggia Classic anymore and should update my sidebar!
another_jim wrote:so regardless of grind size or extraction, you get all the acids and sugars in the coffee.
Thanks for your responses, Jim. Are you sure about this point? Won't large particles have inaccessible, or less accessible, interior regions? Even if acidic compounds solubilize in water quickly there must still be a diffusion step (water going in, compounds coming out) that gets limited by the radius of a particle, right? Still applies if the particles in question aren't spheres.
But if I can interpolate your comments, you're saying there's no way that I can blame high acidity on a bad grinder. I could blame bad shots on a bad grinder, but not specifically sour shots.


#12: Post by Jonk »

Perhaps it's a good generalisation, but I think the real answer is more complex. Look at the tables here:

Talk about a moving target. Which is why this is such good advice:
another_jim wrote:(Please, instantly forget the one variable at a time idiocy -- correlated variables need to be changed together)

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Team HB

#13: Post by another_jim »

Tyme wrote: Thanks for your responses, Jim. Are you sure about this point? Won't large particles have inaccessible, or less accessible, interior regions?
Coffee is spongelike in microstructure, so interior regions of larger particles are less accessible but still wet and extract. Extraction is asymptotic, and unless you have boulders, the acids and sugars are close to their limit within the first 10 seconds of espresso extraction. The heavier compounds are playing catch up.

The detailed chemistry aside, if you grind finer, you will get a less acidic tasting shot. You just need to practice changing dose and grind, and not just in small amounts, but in large steps. It is easier to use an old style basket, which allows for wide dose /grind changes in a single basket. With IMS, Strada, and VST baskets, if you want to make a big grind setting change, you'll also need to step between basket sizes (i.e. if you are getting acidic shots on the VST or Strada 18 gram, switch to the 15 gram, which uses a substantially finer grind setting)
Jim Schulman


#14: Post by mikelipino »

No prob, I've been meaning to move that out of my head anyways. And you're right, it doesn't really tell you what to do, but I was just starting with a possible answer to the question if a large distribution could increase sourness (then leave it for more experienced folks to chime in, I'm fairly new to this myself!). And I think that yes, a wider distribution could add perceived sourness due to the larger tail of boulders. I think that you're on the right track based on the others' comments, grinding finer will increase the extraction and reduce perceived sourness, and dosing down will allow you to extract if you're choking the machine.

If it ends at a place that isn't satisfactory, like you're at 10 g in to be able to pull the shot, you may want to see if your grinder or grind procedure might need to be tuned. It sounds like the added pressure from the auger might be unbalancing things, but would be interested how it's set up. Good luck!

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#15: Post by ShotClock »

One observation that i have, related to Jim's note about baskets:

I have found that some styles of basket - particularly Decent ones, though i haven't tried many precision baskets - provide very little resistance, and finding the right grind setting can be very fiddly. Others, like IMS, seem to provide much more resistance. This results in a much broader sweet spot for grind size.