Frequently Asked Questions
The Extraction of Flavor Components from Roasted Coffee Beans
by Lockhart, H. G. Pickles
Published in the Journal of Food Science 1964, Volume 29, issue 3
This research has been cited and built upon by numerous subsequent studies on coffee brewing and extraction and has become a foundational principle in the field of coffee science.
In this paper, the authors conducted sensory evaluations of coffee samples that had been brewed with varying degrees of extraction, and found that under-extracted coffee tended to be sour or sharp in taste, while over-extracted coffee tended to be bitter or astringent.
Using one fixed recipe to cook all meat doesn’t work, likewise using one fixed recipe for making all coffee doesn’t work. And yet, that is what most people are doing:
In 2016, the Barista Guild of America (BGA) set out to document current practices of espresso preparation using a survey of baristas worldwide, aimed at truly understanding the landscape of coffee preparation in the world.
The findings of the 2017 Barista Guild of America Espresso Survey :
The average barista uses a 1:2 brew ratio when extracting espresso and uses weight for output measurement. The average shot of espresso starts with an 18–20 gram dose, has an output of 36.5 grams, is extracted in 25–30 seconds, at 9 bars of pressure and 200°F, using pre-infusion, through an 18 gram basket.
The heritage Specialty Coffee Association of America (SCAA) definition of espresso:
“Espresso is a 25–35ml (.85–1.2 ounce [×2 for double]) beverage prepared from 7–9 grams (14–18 grams for a double) of coffee through which clean water of 195°–205°F (90.5°–96.1°C) has been forced at 9–10 atmospheres of pressure, and where the grind of the coffee is such that the brew time is 20–30 seconds. While brewing, the flow of espresso will appear to have the viscosity of warm honey and the resulting beverage will exhibit a thick, dark golden crema. Espresso should be prepared specifically for and immediately served to its intended consumer.”
Density.coffee will definitely help if you commit to this program.
It works best if you keep a record of your grind settings at each density. With experience, you can then fairly accurately predict what grind setting will be required for a given density. It’s linear so you only need a few points to generate the line.
The more you use it, the more you will find it gets it right pretty much the first time 95% of the time. Dialing in almost becomes a thing of the past.
Because density.coffee varies all your tools of ratio, dose, yield, temp, time, grind, and pressure relative to the density, which means there is less reliance on grind changes alone. You may find the range of grind settings that you commonly use reduces.
Density.coffee also gives you a really powerful tool for the challenging 5%. Those difficult coffees where it’s stubbornly sour by using addition or bitter by using subtraction. You can do subtle shifts 0.1 to really big shifts 0.4.
That pulls all your levers of ratio, dose, yield, temp, time, grind, and pressure in unison, making it really effective.
Density.coffee also gives you a view of what’s going on with your aging. When you should probably wait before trying, how long it’s good for, and guidance on storage.
A lot of coffee is being made with no regard to extraction changes required for different Roast Levels. Consequently, most coffee is consumed more bitter or sour than it could be. Sugar and milk mask the problems, and people just get used to it. When you can find the sweet spot at every roast level, you can be surprised that you enjoy a wider spectrum of roast levels. If you think you don’t really like dark roasts or light roasts, maybe you just haven’t experienced a sweet one yet.
There are so many advantages to have from measuring density.
Measuring density helps you make the best you can from the coffee you have.
A good quality 100ml cylinder is really cheap, there is little reason not to give it a go.
Get one with a Tolerance (mL) ±0.50 and preferably Borosilicate.
Actually an earlier version of density.coffee included counting the number of beans in the 100mls, to try and factor in bean size variation.
But it was found 95% of the readings resulted in marginal recipe change. Only 5% of the results delivered a significant benefit. The time taken to count the beans significantly degraded the user experience to the point of being completely off-putting.
With experience you can use your eyes, and expect that small beans will behave like a darker roast, they will have been roasted more thoroughly, so subtracting 0.20 from the measured density (extracting less) could improve your initial results. Very large beans behave as if they are a lighter roast. They tend not to have roasted to the same extent all the way through, so adding 0.2 (extracting more) could improve your initial results.
But I would only make those assumptions if I had very little to go with.
You are always better off tasting it and adjusting accordingly (steps 5 & 6).
When it comes to measuring your espresso YEILD, volume is a terrible method compared to using weight.
However, when it comes to measuring DENSITY of a substance, it is its mass per unit volume. You need both tools, volume and weight.
You have to use the right tools for the job. Trying to use one tool alone for every job, would be like a Builder using a hammer to grind coffee.
Good to hear you don’t advocate eyeballing 18g and are at least using scales.
Likewise, a 150-point density measurement is guaranteed to give you better results 99% of the time than your eyeballs for the Roast level.
Before you were blind, now you can see.
Using a fixed 1:2 ratio recipe, fixed 93c temp, fixed-dose, for every roast level of coffee, and relying on grind adjustments alone is worse than playing blind man’s bluff. It limits usable roast ranges to different methods.
For a very light roast on espresso that really requires beyond a 1:4 ratio, a fixed recipe simply hasn’t used enough solvent water. No amount of grinding finer will help, and the coffee will be sour. This results in preventing consumers from using the espresso method for light roasts, relegating many coffees to filter methods alone.
By only using espresso for mid to dark roasts espresso consumers miss out on many wonderful taste experiences.
For a very dark roast on espresso that really requires a 1:1 ratio and a much lower temperature, the fixed recipe has used way too much solvent water, and heat. It is over-extracted, no amount of grinding coarser will help and the coffee will be bitter. Typically dark roast fans use a lot of milk and sugar to cope with the bitterness.
Varying the recipe to one appropriate for the roast level as indicated by the density measurement means every roast level right across the spectrum of very light to very dark, can hit the sweet spot, neither sour nor bitter, for all methods. You are no longer limited to what you can use on espresso. It’s liberating and wonderful.
Measuring density is not a silver bullet, but it is a tremendous tool that helps you understand what your coffee needs, and guides you on how to get the best out of it.
Most home users are not going to have a tool to measure agtron lying around, they are kind of expensive ~$1500 USD for one thing.
They are useful for a roaster, because they already know how the beans were roasted, they just need to now how far to go with the roasting, and when to stop.
But Agtron is not of much use for determining extraction. If you cook a roast at a really high temp, it might be black on the outside, but still tough on the inside. Coffee cooked high and fast will be dark, but still hold a lot of water, be dense, and difficult to extract. A piece of meat cooked long and low is not going to be black on the outside, but it is going to be pull apart tender. Coffee roasted long and low won’t be dark, but it will have lost most of the moisture, be brittle, porous, and extract really easily. So color is not the best tool to use. Measuring density is much better.
You don’t need absolute density by measuring with displacement. No matter how accurately you could measure the density, it would never remove the need to taste the result and adjust it (steps 5 and 6).
Settled density is perfectly adequate for giving you a much better starting point than the fixed recipe.