The short answer
To clean a burr grinder, unplug it, empty the hopper, grind out any beans left in the chamber, lift out the upper burr and brush the burrs, chamber and exit chute with a dry brush. Wash the hopper and grounds bin in warm soapy water, dry them completely, and reassemble. Never put water on the burrs or the motor body.
To clean a blade grinder, unplug it and wipe the bowl and blade with a dry or barely damp cloth. If the bowl lifts out, wash it in soapy water like a dish.
Do the burr routine every 4 to 6 weeks, which is the interval Baratza gives for its own grinders, and sooner if you grind oily dark roasts. Grinder cleaning tablets are an optional extra that strips oil, not a replacement for brushing.
How to clean a burr grinder, step by step
1. Unplug the grinder. Burrs are sharp enough to hurt, and a grinder that starts with your fingers in it is the one accident worth designing out.
2. Empty the hopper, then run the grinder for a few seconds to clear beans from the burr chamber. Unplug it again.
3. Remove the hopper and lift out the upper burr. On most home grinders it twists out by hand: on the Breville Smart Grinder Pro you lift the wire handle and turn it counterclockwise, and Baratza's conical models lift out once the hopper is off. Check your manual if it resists, because forcing a burr carrier is how alignment gets knocked out.
4. Brush the upper burr, the lower burr and the chamber with a stiff dry brush. A small vacuum helps pull out the fines that cling to the chamber walls.
5. Clear the exit chute. Packed coffee hides here, and it is where a slow or clogged grinder usually turns out to be blocked. Push it through with the brush handle or an unfolded paperclip, checking from above and below.
6. Wash the hopper, its lid and the grounds bin in warm soapy water, rinse, and let them dry fully. Breville's manual for the Smart Grinder Pro is specific that no part goes in the dishwasher, so hand wash even the plastic.
7. Reassemble, set a medium grind, and grind a small dose of beans you are happy to throw away. That settles the burrs and carries out anything the brush missed. If you ground very fine before cleaning, re-dial from there rather than assuming the old setting still lands.
How to clean a blade grinder
A blade grinder has no burrs to remove, so cleaning is quicker. Unplug it, tip out the loose grounds, and wipe the bowl, the blade and the underside of the lid with a dry cloth or a soft brush. A barely damp cloth is fine for oily residue, followed by a dry one.
Check whether the bowl comes out. Where it does, KitchenAid's instructions for its blade grinders are typical: wash the bowl and cover in hot soapy water or on the dishwasher's top rack, and wipe the motor housing with a damp cloth only. Where the bowl is fixed, wipe it and never pour water in, because the motor sits directly underneath.
Go carefully around the blade itself. It is not sharp like a knife, but it is sharp enough, and it is fixed to the motor shaft, so clean around it rather than trying to remove it.
How often to clean a coffee grinder
Every 4 to 6 weeks for a full clean with the upper burr out, if you grind most days. That is Baratza's recommendation for its home grinders and a sensible default for any burr grinder.
Roast changes the schedule. Dark roasts leave oil on the burrs and chute, which goes stale, flattens the taste, and gives fresh grounds something to stick to, so a grinder fed on dark roasts wants the shorter end of the range or a monthly clean. Light roasts leave less oil but more static and loose chaff, so they need a quick brush more often than a deep clean.
A brush-out of the chute and burrs every week or two keeps the deep clean easy. Clean between bags as well if you are switching from a dark roast to a light one, because a few grams of the old coffee will otherwise end up in the first cups of the new one.
A blade grinder needs a wipe after every few uses. There is nowhere for grounds to hide, but the oil film on the bowl builds up just the same.
Cleaning tablets: what they do and how to use them
Grinder cleaning tablets are compressed grains made to break up like coffee and absorb oil as they pass through the burrs. Urnex Grindz is the common one, and its directions are simple: empty the coffee out, grind one 35 g dose of tablets at a medium setting, then grind two small doses of coffee to purge the tablet dust before you brew. At current pack prices that works out to about three dollars a clean.
They are useful for what they are, a way to strip oil without taking the grinder apart, and Baratza lists them as an optional last step in its routine, one it highly recommends if you mostly grind dark roasts. They do not clear a packed chute or reach the corners a brush gets to, so they sit alongside the full clean rather than replacing it.
Why not rice
Uncooked rice gets recommended as a free alternative to tablets. Do not put it through a burr grinder. Rice is much harder than roasted coffee, it strains the motor and the burrs, and Baratza advises against it, saying its repair work has shown rice can cause mechanical damage. Its warranty also excludes any use other than grinding whole roasted coffee beans, so a repair after rice is likely to be on you.
Blade grinders are more forgiving, and rice is a common home method for them. Check your manual first, because if it rules rice out, the same warranty logic applies.
Signs your grinder is overdue
Grind times creep up. Grounds come out in clumps or the chute spits rather than flows. The burr chamber smells stale when you lift the hopper. Coffee you know is fresh tastes flat and papery. All of these point to oil and fines built up inside, and in almost every case a proper clean brings the grinder back.
If the grinder stops mid-dose or hums without grinding, unplug it and check the chute before anything else. Baratza lists the usual causes of a clog: grinding a large amount at once, letting the grounds bin fill past about two thirds, grinding far finer than the grinder is made for, re-grinding coffee that has already been ground, very oily or flavoured beans, and beans that picked up condensation from the fridge.