I mentioned this paper in the sticky thread on dosing. I now have a completely rewritten version that I think is clearer and more thought out. It's still on the heavy and pedantic side, but I hope more readable. I'd appreciate any comments or people giving the shot tuning suggestions a spin.

For those who want it short and sweet, there's a forthcoming, more how-to focused article coming up right here

wow. my kind of paper..

a few questions for you.

do you have the list of coffees grouped by molecular weight and flavors? how many coffees did you test and how does it become relevant when blending? will the flavor profile of blends transfer over as scientifically?

next, you are recommending reducing doses from (im guessing here from what most recommend, i dont weigh) a 16-18 gram double to 13grams. wont the shots blond faster, or do you now grind even more fine to compensate?

from what i recall in italy, the shots drip out as opposed to flow, and its rare to see someone tamp with anything but the ones built into the grinders. so, id assume that grinds are really fine and distribution and tamps arent all that precise. i guess with a smaller amount of coffee in there, and a really fine grind, tamping to perfect distribution becomes sort of null. we also have different coffees here, as you mentioned, so doesnt that come into play, or shall we just let our coffee age a bit more, which from what ive seen, takes off that initial bite.

It's not possible to group coffee by their full chemistry. There's three or four labs, using very expensive equipment, trying to find new compounds in coffee. Most of the new ones (roughly chemicals 200 to 1100) are quite exotic, occur at very low concentrations, and nobody is sure when in the roast they occur. Occasionally they score a home run, and find a really low concentration chemical so odorous that it contributes to the overall flavor.

On the more workaday chemistry.
-- The fruit acids are there from the start: citric, malic (apple), and acetic are the biggies, along with longer carbon chain versions of these. In the roast they both break down, and combine with sugars to form alcohols and esters. This taste family corresponds to the acidity in coffee, and is strongest in high grown, washed arabicas
-- The light Maiilard cmpounds are the "baking" flavors -- they develop in the 300F to 390F range of the roast as amino acids react with sugar -- think of browning bread, meats, nuts, wood smoke, malt, etc. Unsweetened, these are sharp bright bitter flavors like lemon peel, ginger, cinnamon, quinine, unripe nuts. They mellow out in the presence of sweetness, becoming toasty, malty, and nutty. These are the hallmark of Indonesian and Indian coffees, as well as some Brazils and South American ones
-- Caramels you know - they develop from around 385F and up from the sugars in coffee. Since dry processed coffees collect sugars from the cherry, they are sweeter and caramelize better.
-- Distillates are the caramels and Maillard compounds as they start searing -- think of your broiler or grill. Good dark roasting is mostly a question of the beans surviving long enough. The highest grown Indos and Indian coffees are best, as well as Mexican coffees. Caribbean coffees are so low grown, they can be used to develop these flavors at medium roasts.

The work on dosing versus yield presupposes that you are always setting the grinder to get actual espresso shots, not something else: roughly 20 to 40 second, .5 to 1 ounce singles, or 1 to 2 ounce doubles, no channeling, and blonding only at the end. If it's not this, it's not espresso.

Jim, I could have missed something in the article, but it seems to me that it would be helpful if you mentioned that generally, solubility increases with degree of roast. See Espresso Coffee section 8.1.2.5; there aren't any solid numbers, because this is sure to vary according to origin factors. It would help to clarify why lighter roasts benefit from lower doses.

Otherwise, this is great. It's really changed my understanding of espresso. I'll keep rereading it, keeping my eyes open for opportunities to give specific feedback.

I was not able to replicate this. My dark roast solubles yields were no different from the light roast ones. This may change when the coffee stales and the light roast's solubles disappear into thin air.

I'm unconvinced that there is no difference between the solubility of a light coffee and a dark coffee. Pyrolysis reactions degrade more and more compounds as the roast progresses, creating more soluble matter. A very general rule for espresso extraction is to increase brew temperature for lighter roasted coffees. Why? To increase the efficiency of soluble extraction to compensate for the lower solubility of lighter roasts.

Perhaps the thinner pucks of the light roasts introduced a higher margin of error, obscuring the differences between light and dark roasts.

I didn't do a lot of dark roast observations, and none further than a rolling 2nd crack. There are reactions in this range that go in the other direction. Dark caramels and maillard reaction compounds polymerize into more and more insoluble melanoidins. The acids simply vaporize. Also, the pyrolysis compounds you mention are mainly the cellulose reducing and becoming soluble. This may only become a large factor at deeper roast levels.

Interesting. The difference in solubility between light and dark might not be that big of an influence as I thought it would be. Nevertheless, the fine grind + low dose/shallow puck formula is maximizing extraction of "balancing" flavor compounds that are present in lighter and darker coffees in similar amounts, but more need to be extracted to compensate for the acidity of lighter roasted coffee.

doesnt pyrolysis occur in high (above 800F) temps and in the absence of oxygen? i suppose it could be argued that while roasting there is some sort of boundry layer around the beans that prevents oxygen from getting too close to the surface, but i cant see how, if at all, this small amount of a reaction would affect the outcome of the bean, except at the infamous 3rd crack, which could correlate to carbonization.

Hi Jim

Great work on the paper, really helped me to understand the whole idea of espresso, how it works, brews and what happens with the coffee.

So I guess overdosing is not a good idea right? Cause it's not about packing as much coffee as you can into the basket. Is this the end of the "pucks with shower screen impression" era?

Cheers,
dsc.