Every day we use ground coffee to make our beloved cup of Java. Yet have you ever stopped and wondered why we use ground coffee as opposed to just whole beans? Or why the size of the grind matters? Or why some people look at you with utter disbelief when you tell them that you use pre-ground coffee?
Well, I by nature do a lot of wondering. So, stick around and find out the answers to all these questions.
Why we Grind Coffee?
The basic goal of making coffee is to get what’s sealed inside the bean (namely, the delicious flavor components and oils) out of the bean. The original method involved boiling the whole roasted beans in hot water while agitating them. With some patience and lots of time you’d eventually end up with a bitter, high-caffeine, coffee solution.
Luckily for us our coffee forefathers eventually came up with a more efficient method to extract the goodies from the coffee! By grinding the coffee beans you help the water to extract efficiently the solubles that are responsible for the taste and aroma in coffee.
Let me explain the logic behind this.
The Efficient Extraction of Solubles
If you take a whole bean and cut it in half you’ll increase the total surface area of the bean. As a result the extraction efficiency is greatly increased. Why? Because there’s more surface area for the hot water to act upon and from which to extract the flavor components.
Now take these two halves and cut them into halves again. Guess what, you’ve just further increased the overall surface area and thereby helped along the extraction efficiency even more. Eventually you’ll end up with just the right grind size for your preferred brewing method.
The benefit of all this “cutting” is that the extraction efficiency dramatically cuts down on the brewing time. But that’s not the only reason why we grind coffee.
Smaller grind particles make for a more complete extraction
The smaller particle size makes the distance from its center shorter. This allows not only for a more efficient extraction, but also for a more complete extraction of soluble flavors contained within the particle.
Why You Should Not Buy Pre-Ground Coffee
A roasted whole coffee bean is a beautiful, protective package that keeps the coffee oils exactly where we want them, namely, inside the bean. As long as you don’t mess with the beans the flavor components, which are very delicate, volatile and water-soluble substances, will be safe. However, break the protective shell and all bets are off.
Introducing the four great reasons why NOT to buy pre-ground coffee.
Coffee oils are very delicate, which makes them an easy victim of contamination. Whatever odors are around ground coffee will taint it in ways that will not contribute to your coffee tasting experience.
The cells inside the roasted coffee bean contain approximately 1,000 different volatile aromas and flavors. Once ground the volatile aromas are immediately released and they react with oxygen in the air (oxidation). After 15 minutes ground coffee loses about 60% of its aroma.
Coffee oils are water-soluble. That’s a good thing or we’d have a very had time trying to get the oils out of the bean. This fact however poses a great problem for ground coffee. When ground coffee is exposed to moisture in the environment it immediately starts to dilute the oils.
4) Carbon Dioxide Depletion
Increased surface area permits for greater carbon dioxide (CO2) gas liberation. During the roasting process a lot of CO2 is created. Since the bean is porous, some of it is lost during the cooling process. Much of it, however, is retained within the cells of the coffee bean. This CO2 plays an important role in that it is the main method for getting the essential coffee oils into the coffee once they are released.
The Problem is that the increased surface area created after grinding permits for greater CO2 gas liberation. In fact within 60 seconds of grinding 80% of this gas is released into the air. Wait too long after grinding the coffee and you’ll trade your Ferrari for a go cart with underinflated tires.
The Solution: always grind your coffee freshly just before brewing. Follow this rule and you’re one step closer to paradise in a cup.
Three Factors that Can Influence the Grind
There are some factors that can influence the way roasted coffee beans behave when you grind them. Let’s look at three most important ones here.
1) Roast Level
In general the more light the roast, the more pliable and tenacious the bean. Thus a lightly roasted coffee is going to be more pliable and tenacious than a darker roasted coffee. The reason for this is that the more you roast a coffee, the more moisture is lost during the roasting process, which makes dark roasted beans more brittle.
2) Bean Brittleness
The method used to process coffee influences how the beans at the same roast level grind. Coffees processed using the dry process grind differently than coffees using the wet process.
New Crop vs. Past Crop
When the coffee was harvested makes a difference to how it will grind. Usually coffee is available for roasting three to six months after harvest. The goal is to roast the coffee as soon as possible, since green coffee gets woodier and woodier with every month that goes by. As you can imagine this is one of the factors that then affects how the coffee ultimately roasts. Coffee beans from new crop coffees produce less fine dust particles than from past crop coffees.
Coffees grown at higher elevation (about 1,800 ft and above) grind differently than coffees grown a low altitude (mostly Robusta). The reason for this is that the higher the altitude, the slower-maturing the beans, and therefor the harder and denser its substance.
Arabica vs. Robusta
The difference in cell structure between Arabica and Robusta beans also makes a difference in the number of particles produced after grinding.
3) Air Quenching vs. Water Quenching
When the beans come out of the roaster they must be cooled down immediately to prevent over roasting. This is called “quenching” in the coffee industry.
Some roasters add water to the air stream that cools the beans to kick off the cooling process. However, “water quenching” (if done improperly and indiscreetly) damages the surface of the roasted beans and can add water lost during the roasting process back into the beans. In contrast, air-quenched coffee is cooled by pulling air through the beans while they are stirred; no water is used during air-cooling.
The take-way here is that the method that is used to cool roasted coffee can affect the beans in ways that can ultimately result in inconsistent grind particles.
Coffee Grind Chart
One of the many benefits of grinding your own coffee is that you’ll be able to accurately “calibrate” the grind depending on your preferred brewing method and type of coffee. Moreover, once you’ve learned what works with you system of brewing you can easily and consistently replicate it. You will no longer be at the mercy of some generic “one size fits all” grind.
|Extra Coarse||Reminds me of really small pebbles.|
|Coarse||Chunky, distinct particles, like coarse sea salt.|
|Medium||More the texture of coarse sand.|
|Fine||Smoother yet. More like sugar or salt when you rub it between your fingers.|
|Extra Fine||Not as fine as flour or powdered sugar, but definitely in that ball park.
You can still feel some grit.
|Turkish Grind||Like flour, very powdery.|
Match the Grind Level to Your Brewing Method
You should always match the size of the grind to the particular brewing method you’ll be using.
The amount of time that water and coffee needs to be in contact with each other is directly related to the particle size of the grind. The finer the grind, the more surface area of the bean is exposed to water. The more surface area, the less dwell time is needed. Consequently, if you’re using a brew method that uses a longer dwell time, you’ll need to use a coarser grind.
Following is a chart of brewing methods and their recommended grind level.
If you still have difficulty finding the right grind size go to a local roaster or coffee retailer and ask them to grind you up a small sample of coffee for your brewing method of choice. Prepare coffee with it at home, and if you like the result try to match your grind to it.
The Best Way to Measure Coffee
The best way to measure coffee is by its weight and not by its volume.
The problem we’re trying to overcome here is the following. Coffee beans lose water content and swell in size during the roasting process. The darker the roast, the more water content is lost and the more swelling takes place. Hence 40 dark roast coffee beans from brand X are going to weigh less but take up more space than 40 light roast coffee beans from the same brand X.
So, if you weigh your coffee beans before you grind them you’ll overcome two problems. Firstly, you’re measurement is going to be far more accurate for you’re taking into account the varying bean densities. Secondly, you don’t have to rely on visual approximation, which you would when using a “standard coffee scoop”.
What’s the best way of getting started measuring your coffee? Invest in an accurate digital scale that measures both in grams and ounces. Make sure it has a way to zero out the scale and goes up in 1 gram increments. Start with the standard measure that is appropriate for your favorite brewing technique.
Over time you’ll then learn to add to or subtract from the weight of the grind according to your personal taste.
New Rules for Grinding
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