How to Calibrate Your Coffee Grinder to Make Perfect Espresso

Calibrating your commercial coffee grinder is something that should be done every morning prior to opening. And if the weather is changing, it may be appropriate to adjust it during the day. In many coffee shops and espresso bars, no one bothers to do this. The result is inconsistent espresso.

If you have excellent coffee beans, an excellent machine, and a skilled barista, but do not have the coffee grinder adjusted for the day's conditions, the drinks produced can be of poor quality: either watery and weak, or bitter and burned. In fact, most of the time that you get an espresso that is of pour quality, the reason is that the grind was wrong for the atmospheric conditions at the time. No amount of tasty syrup or fancy latte art can hide the poor quality of espresso that was badly extracted because the grind was off.

The good news is that calibrating your grind is very simple to do. Unfortunately, many coffee shops and espresso bars don't bother to do it. All you need is a kitchen timer. We prefer a timer with a digital readout that has large numbers that are easy to read. You may want to get a kitchen timer with an adhesive back, and stick it to the front panel of your commercial espresso machine. This way, the timer will always be right there, and handy for checking your grind throughout the day.

Optimal Extraction Times

The optimal espresso is 30 seconds for a 1 ounce Espresso, and about 20 seconds for a 2/3 ounce Ristretto, each using a single dose (1/4 ounce) of coffee, and the single group handle. It should also take 30 seconds to extract a 2 ounce Doppio, and about 20 seconds for a 4/3 ounce Double Ristretto, each using a double dose (1/2 ounce) of coffee, and the double group handle. (See the tables in our article "Programming Shot Sizes on Your Commercial Espresso Machine.")

If the extractions go faster than this, not enough flavor will have been extracted, and the drinks will be weak. When the grind is too coarse, the grounds will not pack tightly together, and the water will pass through them too quickly. The extraction will be too fast, and the drinks will be weak. You must make the grind finer.

If the extractions take longer than 30 seconds, they will be bitter. When the grind is too fine, the grounds will pack too tightly together, and it will be harder for the water to penetrate the coffee puck. This will result in an extraction that is too slow, hence bitter drinks. You must make the grind coarser.

Adjusting for Weather

Coffee grounds will absorb water from the air. This is one of the reasons that you should empty the chamber of your commercial coffee grinder every night, and start with fresh coffee beans in the morning. On a humid day, or on a day that becomes humid, the coffee grounds will absorb water from the air more quickly than on a dry day.

If you do an extraction with coffee grounds that had absorbed water from the air, the water from the espresso machine will not penetrate it as quickly. This will result in a slower extraction than normal. Essentially, as a day grows humid, the effect on extraction is the same as if the grind got finer. Humidity will slow the extraction down. You have to compensate by making the grind a little coarser.

Similarly, on very dry days (or as any particular day becomes dry), the espresso will tend to extract slightly faster. The effect of dry air is the same as if your grind were coarser. You will need to compensate for dry air by making your grind a little finer.

You should calibrate the grind first thing in the morning, every morning before you open. And if the weather changes during the day, or if you think that conditions have changed, you should time a few of your shots to see whether you have to adjust the grind.

Calibrating Your Grinder

We prefer to calibrate using a Doppio (Double Espresso). Load and tamp a double dose of coffee (1/2 ounce) into the double group handle, and lock it into the grouphead. Push the programmed button for a Doppio (see our article "Programming Shot Sizes on Your Commercial Espresso Machine"), and at the same time, start the kitchen timer.

If the grind is correct, the flow will start at about 4 seconds. The flow will be smooth and constant, and the crema will be golden-brown in color. If the grind is too coarse, the flow will start in 3 seconds and will be noticeably fast and will not be smooth. There will be very little crema. The crema will be pale, and will quickly dissolve into the espresso. If the grind is too fine, the flow might not start for 5-6 seconds. The extraction will continue well past 30 seconds. The crema will be dark and might have large bubbles and dark streaks in it. The brew will taste bitter.

The grind can be easily changed by rotating the collar on your commercial coffee grinder. If you don't remember which way to rotate the collar, you might need to take the hopper off of your commercial coffee grinder to read the "legend" on the collar. Don't forget to close the gate before removing the hopper.

The collar should have a "legend" on its top surface that indicates which way it should be rotated to make the grind finer and coarser. The "legend" may be arrows with "+" and "-" signs. For most commercial coffee grinders, rotating the collar clockwise will make the grind finer, and rotating the collar counterclockwise will make the grind coarser. The collars on commercial coffee grinders will be locked in place. There will be a release switch somewhere around the collar that must be pressed to allow you to rotate the collar.

First, empty the chamber of the (previously ground) coffee by repeatedly pulling the doser lever until no more coffee comes out. Find and press the collar release, and rotate the collar in the appropriate direction to make the grind coarser or finer, as needed. Put the hopper back onto the coffee grinder, and open the gate. Grind enough beans to fill the doser, and load up another Doppio.

Re-time the new Doppio. If it needs further adjustment, repeat the process. You can save the ground coffee that you empty from the chamber for uses other than espresso. You need not discard it. Use it for regular or iced coffee.