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I've noticed that at the same grind setting (medium grind), some coffee beans produce a ton of dust when ground, while others barely have any dust. I'm thinking it has to do with the roast level, but I'm not completely sure.
What factors affect how much dust is produced when grinding coffee beans?
(1) Burr grinders are known for more precision and consistency than blade grinders.
(I haven't tried a blade grinder, but Specialty Coffee says
Now, once the grinder is loaded, don't just hold the button down and let it rip... use short bursts of a few seconds each so the coffee doesn't overheat.
Make sure you have a hold on the top of the unit and give it a shake during bursts so that the grounds get well mixed while grinding. This will make the grind much smoother and consistent.
Be careful that some "burr grinders" have blades and burrs.)
(2) Cold beans grind more consistently. Per NY Times:
But to achieve consistent flavor you may just need to chill your beans before grinding them. Colder beans produce smaller, more consistently sized particles when ground, yielding more flavor from less coffee, according to a study published in Scientific Reports.
As room temperatures vary and grinders heat up with use, the consistency of the resulting grind changes. That’s a problem, because water extracts flavor from smaller coffee grounds faster than bigger ones. An inconsistent grind means sour taste from the small grains, and a bitter one from the big, all at the same time.
(But I'm pretty sure that last sentence is reversed.)
Note that some grinders heat up with use.
(3) Different bean types, roasts, and ages might produce more dust than others when ground, but I don't have good info on that.
In addition to the factors mentioned by Jerry101 you are very right in assuming that it has to do with the roast level. The grinder is of course to most important variable here but I'm assuming you are using the same grinder for all your roasts or rather you are comparing results of different beans using the same grinder.
The temperature has an effect, cooler beans create a smaller and more evenly distributed grind (on the same settings). Everyone who has ever worked as a barista knows this. During the day in a commercial setting the grinder will heat up resulting in a change in grind size. That is why you should check your extraction on regular intervals, when working in a café. See also the study linked by Jerry101 and this article on Barista Hustle.
However in my opinion and experience the most important factor in every day situations is indeed the roast level. Just try to squish beans of the same origin but different roast colors (any specialty coffee shop will likely have either Ethiopian, Kenyan, Colombian or ... beans in an espresso blend and as a filter roast) between your fingers and you will notice that the darker beans will crush more easily. They are much more brittle, because they have less water left in them and thus break creating more dust/fines. If you were to freeze your beans (which you should do very carefully, in a sealed and vacuumed package) the temperature would likely be as important or maybe more important than different roast levels.
The bean type (origin) has likely no or only a very small effect on the grind. This is discussed in both sources linked to.
