What you can and cannot make this way
Every method on this page breaks beans by force rather than by cutting them to a size, so all of them give you an uneven grind. That is not a reason to skip them. It is a reason to be careful about which drink you point them at.
Cold brew comes out genuinely well. French press comes out well. Drip and pour over are workable if you sift, which is covered further down. Espresso is out of reach, and no amount of technique changes that.
The espresso limit is worth understanding rather than just accepting. An espresso machine pushes water through a compressed puck at around nine bar, and the puck has to resist that evenly for 25 seconds or so. A grind with big chunks in it leaves channels for the water to race through, and a grind with too much dust blocks up and chokes. You need both fine and consistent at the same time, and no kitchen tool does the second part.
So the useful question is not how to grind beans without a grinder. It is what you can brew with the grind you are able to make, which is a much easier question to answer well.
Put the beans in the freezer first
This is the one piece of advice here with a peer-reviewed paper behind it, and it is the step most guides leave out.
In 2016 Erol Uman and colleagues published a study in Scientific Reports (volume 6, article 24483) that ground coffee at four temperatures and measured the particle sizes that came out: room temperature at 20 C, a domestic freezer at minus 19 C, dry ice at minus 79 C, and liquid nitrogen at minus 196 C. Two findings matter here. The modal particle size fell by 31 percent between room temperature and liquid nitrogen, and the spread of particle sizes got narrower as the beans got colder. The narrowing was clearest in the step from room temperature to freezer, which is the only step you can actually perform at home.
Their other result is worth knowing because it saves you worrying about the wrong thing: bean origin, variety and processing method made almost no difference to the grind profile. Temperature did.
One honest caveat. That study used a Mahlkonig EK 43, a commercial burr grinder, not a blender or a pestle. What it measured was how the bean itself fractures when it is cold, and cold beans are more brittle, so they shatter instead of squashing and tearing. That mechanism should carry over to any method that breaks a bean by force, and squashing and tearing is exactly what makes a blender grind so ragged. But nobody has run the experiment on a blender, so treat it as well-founded rather than proven.
In practice: seal the beans in a bag, give them 20 to 30 minutes in the freezer, and work with them straight out of the cold. Do not leave them in there for weeks in a bag that breathes, because coffee picks up freezer smells and moisture.
The six methods, best result first
MORTAR AND PESTLE. The best result of any method here, and the slowest. Work in small batches, around two tablespoons of beans at a time, or the ones at the top never make contact. The technique is press and roll rather than pound: pounding sends beans out of the bowl and produces dust, while leaning your weight on the pestle and rolling it around the wall crushes them progressively. Expect eight to ten minutes for a single mug. You have real control over the size, which is why it wins.
ROLLING PIN. The most even coarse grind you can get in a normal kitchen, and much faster than a mortar. Put the beans in a zip bag, push the air out, and lay it on a chopping board with a tea towel underneath to save your worktop. Crack them first with a few firm presses of the pin, then roll with weight on it, redistributing the beans every few passes. This is the method to use for cold brew and French press.
BLENDER. Fast and the most uneven. Pulse it in bursts of two or three seconds rather than running it, and shake or tilt the jug between pulses so the beans that have settled at the bottom get moved. Do half a cup at a time at most. Blade speed generates heat, which drives off aroma while you work, so short bursts help twice over. This is where the freezer step earns the most.
FOOD PROCESSOR. Same principle as a blender and usually a slightly worse result, because the bowl is wide and shallow so the beans skitter out to the sides away from the blade. If you have both, use the blender. If the processor is what you have, use the smallest bowl and the pulse button.
HAMMER OR MEAT MALLET. Crude, coarse, and perfectly fine for cold brew, where the grind wants to be coarse anyway. Bag the beans, put them on a board, and tap rather than swing. Full-force hits burst the bag and turn the bottom layer to powder while the top layer stays whole.
CHEF KNIFE. Good for one cup and nothing bigger. Lay the flat of the blade over a few beans and press down with your palm on the spine to crack them, then chop the pieces down like garlic. Slow, but you can see exactly what you are producing, which none of the powered methods let you do.
A note on spice grinders, since people suggest them: a spice grinder is a blade grinder, so it belongs in the blender category rather than being a shortcut around this whole page. It works. It will also flavour your next batch of cumin with coffee and your next batch of coffee with cumin, so keep a second one if you go this way.
Why improvised coffee tastes bitter and sour at once
People describe the result of a blender grind as harsh, or muddy, or just bad. What is usually happening is more specific than that, and knowing it tells you how to fix it.
An uneven grind contains both dust and chunks. Dust has enormous surface area for its volume, so water strips everything out of it fast, including the bitter compounds that come out last. Chunks give up their sugars and acids from the outside and never fully release what is inside, so they contribute the sharp, sour, thin flavours of an under-extracted cup. Both are in the same brew. You are tasting over-extraction and under-extraction simultaneously, which is why the cup does not taste like a normal bad coffee and cannot be fixed by brewing longer or shorter.
The fix is to remove one end of that range. Tip the grounds into a fine kitchen sieve over a bowl and shake for 20 seconds. What falls through is the dust. Brew what stays in the sieve, and throw the dust away or save it for something that does not care, like adding to a chocolate cake. You lose perhaps a fifth of your coffee by weight and the cup improves more than that sounds like it should.
If you have a coarser sieve or a colander as well, you can go further and take the boulders out of the top too, then re-crush just those. Two sieves gets you surprisingly close to a real grind. This is genuinely what a laboratory particle-size analysis does, only with money.
Match the brew to the grind you can make
Brew methods differ enormously in how much they punish an uneven grind, and choosing the forgiving one is worth more than any amount of extra effort at the crushing stage.
COLD BREW is the most forgiving thing you can do with a bad grind, and it is not close. Steeping for 12 to 18 hours gives even the chunks time to give up most of what they have, so the gap between the dust and the boulders narrows to something you can barely taste. Coarse and rough is exactly what this method wants. If you have a bag of whole beans and a rolling pin, make cold brew.
FRENCH PRESS is next, for the same reason on a shorter timescale. The one thing to watch is that the extra dust slips past the mesh and settles in your cup as sludge. Sift first, and decant rather than pouring the last inch.
AN AEROPRESS handles a rough grind better than its size suggests. The contact time is short, the pressure does some of the work, and the paper filter catches the fines that would otherwise muddy the cup. If you own an AeroPress, it is the best drinking coffee on this list after cold brew.
POUR OVER AND DRIP are the ones to be careful with. These rely on water flowing through a bed of grounds at a steady rate, and dust migrates down and blocks the pores, so the brew stalls and then over-extracts while it sits there. Sifting is close to mandatory here. Grind coarser than you think, and if the drawdown crawls, accept the cup as it is rather than stirring it.
MOKA POT sits in the middle. It wants a fine grind, which improvised methods produce badly, but it is more tolerant than espresso because the pressure is much lower. Sift out the boulders, use the fines, and do not tamp.
When to stop improvising
All of this is a bridge rather than a destination. It is worth being honest about how short the bridge is.
A manual hand grinder costs about 40 dollars and beats every method on this page comprehensively, including the mortar. It takes 30 to 60 seconds of cranking per cup. If you are grinding by hand anyway, you may as well be doing it with burrs.
On the electric side the entry point that people actually keep is around 150 dollars, which is where the Baratza Encore sits. Below roughly 100 dollars, electric grinders are usually blade grinders wearing a burr grinder's price tag, and you are back where this page started.
There is one more option that most coffee writing is too proud to mention. If your only tool is a blender and you mainly drink filter coffee, buy pre-ground from a roaster who grinds to order and use it within two or three weeks. Ground coffee stales faster than whole beans, that part is true, but a slightly stale even grind makes a better cup than a fresh ragged one for anything except espresso. Freshness is one variable. Grind consistency is a bigger one.