Brewing coffee is about extracting flavor from the beans. Extract too much and the coffee is bitter and acidic, extract too little and the coffee is thin and sour. Coffee extraction is a function of three things; the temperature, the brew time and the size of the grounds.
“How to brew” coffee articles focus on temperature and brew time. So we know that brew water should be 200 +/- 5 F degrees. We also know that for drip brewing we should pulse the water into the basket and stretch out brewing and for immersion brewing we should stir and wait for 4 minutes. However, very few articles talk about the relationship between temperature, brew time and ground size.
If you are using the right temperature and the right brew time for your brewer and still think the coffee is too sour or too bitter then you should look at changing how you grind your coffee beans. Even a small change in grinding can change the flavor of your coffee.
A common assumption is that all coffee grinders are the same. It isn’t true. There is a dramatic difference between coffee ground in a blade grinder and coffee ground in a conical burr grinder.
Look at the grounds before you add water. Make sure they are all about the same size. If not, you need a better grinder.
Using a grinder that produces even grounds is critical. If the grinder produces some large, some medium and some fine chunks, the large grounds are going to under extract and the small grounds are going to over extract. Over and under extraction do not cancel each other out.
Blade grinders do not produce even grounds. Flat blade burr grinders are better but if you are brewing high end specialty coffee you should have a conical burr grinder. Good conical burr grinders start at around $100.
Sharp Burr Blades
Grinder burrs wear down and sometimes get chipped. Dull or chipped blades will produce uneven grounds. Open up your grinder and check the blades. Grinder blades should be sharp and chip free. All reputable manufacturers sell replacement burrs for their grinders. If you have been using the grinder for a long time it may be time for new burrs.
Coffee grinders need to be cleaned regularly. Grinders build up old grounds and coffee oils that turn rancid. We have had customers who switched from a dark roast to a light roast complain about off flavors. We have found that one source of bad flavors in coffee is dirty grinders.
For home grinding we suggest that you do a light cleaning after every bag of coffee and a heavy cleaning after every third bag. (There is nothing magical about using bags as a memory device, you could do it every month or whatever works for you.)
Light cleaning is getting the old coffee grounds and oil out of the grinder. You can do it two ways. Pull the plug (we had an employee who didn’t – old four fingers), take off the hopper and the top burr. Clean the top burr with a rag and push out any stuck coffee with a chopstick. Do the same thing to the bottom burr. Run a brush or a rag into the coffee chute and clean out any grounds. Then take your vacuum cleaner hose and suck out the burr chamber and the chute.
Another way to do a light cleaning is to run a grinder cleaner through the machine. Two popular cleaners are Full Circle and Grindz. You pour them in, run the grinder and the gunk comes out the chute. Before you use the grinder again, grind some old coffee so you don’t get grinder cleaner in your brew.
Some sites recommend cleaning by grinding rice. If you have a good conical burr grinder, don’t do it. Rice is harder than coffee beans and you may ruin your grinder.
Periodically you should do a heavier cleaning. The process is the same but you take the grinder apart as much as you can, clean the burrs, the burr chamber, the hopper and the chute with a slightly damp cloth. You may have to add a little detergent to the cloth if the oils don’t come out. After you reassemble the grinder run some coffee beans through it to stop the burrs from rusting.
There is a lot of confusion about the size of coffee grounds. In general the size of the grounds depends on 1) the filter you are using and 2) your tolerance for solids in your coffee cup. For example, the standard advice for French Press brews is to use coarse ground coffee, because most French Presses have coarse metal filters. However, it is possible to buy a French Press with a fine metal filter which will allow you to use a finer grind.
Here are some general rules for grinding but you need to adjust to your filter and your taste.
Coarse ground coffee works well for Cold Brew, Cowboy Coffee and French Press coffees. Coarse ground coffee is about the same size as kosher or sea salt.
Medium-coarse grounds work well for Clever, Café Solo and Chemex brewers. Medium-coarse grinds are smaller than kosher salt but larger than table salt.
Medium ground coffees work well for automatic drip coffee makers, Medium ground coffee is about the same size as table salt.
Medium Fine Ground
Medium fine ground coffee works well in siphon coffee makers. Medium fine grinds are smaller than table salt but larger than fine sand.
Fine ground coffees are needed for manual pour over, Aero Press, espresso and moka pots. Fine coffee grounds are about the same size as fine sand.
Extra Fine Ground
Extra fine ground coffee is used for Ibex brewers (Turkish coffee), and is about the consistency of powdered sugar.