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In general, I prefer burr grinders for grinding coffee beans, but sometimes I have to use a rotary grinder. I'd like to understand how to best use the rotary grinder for grinding coffee beans.

I find burr grinders generally produce a superior result in terms of grind consistency, less heat generated, and therefore final product is better. Sometimes in a pinch, however, I need to use a rotary grinder (e.g., it's the only grinder around; burr grinder hopper is full of other beans; flavoured beans that I don't want to pollute the burr grinder; testing to see if a newly roasted batch of beans is "ready", etc.) -- and there are some advantages of rotary grinders.

I'd like to use the rotary grinder in such a way as to make the ground coffee particle size as even as possible. Is this even possible? I find that, no matter how I use the thing, I end up with some very large chunks (even whole beans) and some extremely fine powder. The result is only usable in filter coffee (drip/pour-over), but it simply doesn't "work" as well as when the ground coffee particle size is more even.

I have searched for techniques or recommendations, but I find exactly nothing helpful on this, but I believe there must be some way to optimize the use of a rotary grinder. I have tried things like...

  • Pulsing the machine. Turning on for a second, then letting the blades come to rest, then pulsing some more, until I achieve approximately the grind I'm looking for;
  • Shaking the grinder up and down during the grinding;
  • Revolving the grinder around in a circle the opposite way that the blades are spinning;
  • Using more or less beans in a single grinding session ("half full" seems to work best for me)

All of these seem to have minimal / marginal benefit. Is there any way to improve the coffee bean grind consistency using a rotary grinder?

  • I've tried all the methods you list as well. I agree with the accepted answer. I might only add you could sift the ground coffee through a strainer to at least separate out the largest chunks. – PJNoes Nov 3 '15 at 23:27
  • Please check this answer. It is not a straight answer, but it may help. – MTSan Aug 13 '16 at 13:38
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"Using more or less beans in a single grinding session" will yield the most bang for buck, usually. However, this is highly dependent on your particular rotary grinder. Rotary grinders are like miniature blenders. Just like in a full size blender trying to make a milkshake or something, if you over- or under-fill the blender, then the blade won't be able to mix the ingredients as it cuts through them. Cheap grinders won't be designed to mix very well as they grind, so with terrible grinders, you probably won't see much benefit to your strides.

You need to experiment with your particular blade-style rotary grinder to see how much you can add without prohibiting movement once the beans are fully chopped up, and without leaving too much movement where they just bounce around inside. Too much room will create friction from the grinder chamber sides, and will start to warm up the coffee oils. Too little room will result in the same bean being over-ground (too much friction from the blade), and you'll get coffee paste in the inner center of the grinder chamber.

Achieving consistency and repeatability to the level of a fast-food chain will be impossible, as rotary grinders are way to sensitive to how many beans you put in, as well as size and shape of the bean, how hard the bean is (age of bean), lunar phase, etc. Maybe this is why all the big coffee chains use more expensive burr grinders in-store (not that the coffee is better, which it arguably is, its just more predictable). Some fancy rotary grinders have timers and knobs and levers to set so you don't have to count to yourself before you let go of the grind-button. That helps, but is far from a silver bullet.

  • Lunar phase! I had somehow overlooked that as a factor. ;-) Excellent points about different sizes and styles of the grinder making a big difference, and being dependent on nature of the beans themselves. I think you're right about the quantity of beans being a dominant factor in grind quality. – hoc_age Sep 25 '15 at 14:44
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Well, with any type of grinder you will always have what are called "fines." A blade grinder will undoubtedly produce more, but if I were you I would grind your particle size as fine as you can go. That way your deviation between the particle sizes is closer together, and should be easier to extract everything more even. Even if you have to shorten extraction time, you should see a better cup in the end result.

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From what I could find, blade grinder is no match to burr grinder, no matter what technique or special shaking/tilting way you use. When I use blade grinder - I find pulsing helps. Pulse for couple of times, look at the result. Pulse couple more times... and so on, until you are (sort of) satisfied with the result.

If you really want to get creative, you could pulse for some time, shake the grinder. That will bring the roughest parts to the top. Remove them into one container. If the rest is ok - put that into french press (or w/e way you make your coffee). Put the undergrinded part back and repeat. That may or may not prove worthy of your time, but it is an idea that crossed my mind, when I used rotary (blade) grinder.

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I pulse, but start off with very staccato pulses/short time intervals. This allows the beans and pieces to settle often and be in contact with the blades, making the grind more even. After the really big chunks are gone, then I might hold the button down a bit longer. I'm pretty happy with the uniformity I get doing it this way.

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