Why is my coffee strong or weak?

When brewing coffee at home, I started to be very curious about the different parameters that made my coffee weaker or stronger. As I started reading and testing, I found that there is a lot behind this seemingly simple question.

What makes a cup of coffee weaker or stronger is the total dissolved coffee solids (TDCS). The more TDCS the stronger your cup of coffee will be. This is mostly influenced by the coffee to water brew ratio, being the usual a range from 1:12 to 1:18 for pour-over and drip brewing methods.

Let’s dive more into what this means through the rest of this post. We will also talk about the difference between strength and extraction, all the factors that influence both, and some common related questions.

Strength and extraction, and how it influences your coffee flavor

I used to associate a bitter coffee with a strong one, and/or a sour or acidic coffee with a weak cup of coffee. As I started reading and testing I found that there is not necessarily a correlation.

You see, the acidic or bitter taste is related to the extraction or yield. Extraction is how much of the coffee mass you extract from the beans when brewing.

An under-extracted coffee has lots of acidic fruity acids. While an over-extracted coffee has, as well as the acidic components, also the bitter ones, which tend to mask the lighter and fruiter flavors. This is why over-extracted coffees taste bitter, while under-extracted taste acid or sour.

Now, when it comes to weak or strong coffee, this is related to the number of coffee solids dissolved in relation to the amount of water. It has to do with the concentration of coffee, and not necessarily with the type of coffee solids extracted: fruity acids or bitter compounds.

Strong coffees have lots of total dissolved coffee solids (TDCS) and therefore give a strong flavor. According to Easto (2018), TDCS range from 1.15% to 1.35%.

I was quite surprised to see this seemingly low numbers. It means that when you drink coffee, black coffee at least, it is mostly water. But the few TDCS that are present give immense flavor. A seemingly small variation in TDCS is the difference between perceiving a coffee strong or weak.

So when you refer to strong coffee, you can have a strong flavor that can be bitter or acid, or a balance between the two.

On the other hand, weak coffee, has fewer total dissolved solids, and therefore it tastes watery. But this watery flavor, can also be bitter, acid or a balance.

It sounds kind of ironic, but you can have an overextracted weak coffee. Meaning it will have extracted lots of the bitter compounds of the coffee, but be present in small dose in relation to the amount of water.

On the other hand, you may also have a strong underextracted coffee. Meaning you will have lots of coffee in relation to water, but that coffee has a lot of the bitter compounds. This will taste watery but bitter at the same time.

At the end, a balance between the two is what you are looking for and it mostly depends on personal preference.

The following graph explains this more. It was developed by a Dr. Earl E. Lockhart, director of the Coffee Brewing Institute (CBI), in the 1950s. It is amazing that still today it provides lots of guidance to understand more about extraction and strength.

Coffee to water ratio

This is one of the main components that influence how strong or weak a cup of coffee will be.

What is generally said is that you should start with a ratio of 1 to 15. This means that for every part of coffee you will need 15 parts of water.

The best way to calculate this is by using a scale. You can weight the amount of coffee, for example starting with 16 g of ground coffee, and then multiply that by 15, to calculate your amount of water needed. For this example you would need 240 grams of water, which is what I usually use at home when brewing 1 cup of coffee.

If you do not have a scale, you can measure your dose of coffee by using 2 tablespoons of coffee for every 6 ounces of water for a starting point. Each tablespoon is approximately 6 grams of coffee, although this can vary depending on the grind of the particle. So 2 tablespoons for every 6 ounces of water would be a relation of 1:14.

Try coffee this way and then see if you should add more or less coffee depending if you want it stronger or weaker. The more coffee you add the stronger it will taste.

You can use this table as a general guidance:

Coffee to water ratio table, for every two table spoons of coffee. The numbers were rounded up or down to make it more practical.

The following omni table can be used as well for this calculation. It suggests different brew to coffee ratio depending on the brewing method as well as a suggestion for regular or strong coffee.

Factors that affect extraction

As said before, extraction refers to the type and quantity of the different soluble coffee solids that are taken out from the bean. Extraction or yield is an estimate of the percentage of mass from the coffee bean that was taken and delivered to the brew. This is different than total dissolved coffee solids (TDCS) which states the number of coffee solids that are dissolved in the brewed coffee.

The following parameters affect the extraction of the coffee, and therefore the flavor as well.

Brewing time

Brewing time will determine how much water and coffee are in contact. Ground coffee needs to be in contact with water in order for the water to dissolve and remove the coffee soluble solids from the ground coffee.

The longer the coffee is in contact with the ground beans the more it will extract. But be careful, because it can also affect the bitterness of the coffee as it can also influence the type of coffee solids that are extracted.

When preparing a coffee using a Kalita method, I was surprised to see the difference when I brewed in under 3 minutes, then when I brewed in about 3 minutes and 45 seconds. The first one was evidently more acidic than the second one.

Using a medium grind, and water between 90 Celsius to 96 Celsius (196 and 205 Fahrenheit) being poured with a gooseneck kettle, I was putting all this theory to the test without realizing it. The difference in time was subtle, less than 1 minute. But the difference in flavor was definitely perceivable.

The following table illustrates approximate brewing times for different methods as well as the water temperature.

Below and above these levels you will get under-extracted coffees or ones with lots of fruity acids and sugars, but little dry distillates or Maillard compounds which are the ones that impart bitterness.

Above these levels, you may get an over-extracted coffee, which can taste bitter because it has lots of bitter components that mask off the fruity acids.

It is said (Easto, 2017) that generally, you will have an acceptable cup that has between 22% and 18% of extraction of the solids present in the coffee bean.

Espresso, unlike pour-over brewing methods like Kalita, Chemex, or V60, delivers coffee by passing water at high pressure through finely-ground coffee. The time it takes to do this is very small, and therefore a difference in seconds may be determinant for the coffee to taste right or not.

Water temperature

Another very important factor is water temperature. As you can see in the table before, water that is less than 195 F (90 C) can deliver acidic coffee, while above 205 F(96 C) can turn a cup bitter. It is the same principle as with brewing time. Cooler water will not extract all the bitter components, while hotter water can over-extract them and give a bitter flavor.

Size of the grind

Finer grounds will have more surface that will be exposed to the water, therefore will have more contact with water. Also, when the grounds are finer, the time it takes to brew is longer because water drips down slower.

Type of mill

The type of mill also influences the extraction and strength of your coffee. A blade mill does not grind even, and you will have large and small particles mixed together. This will give less consistency between one cup and the next. A burr mill, on the other hand, gives more consistency between cups, but also between the grains of coffee. The difference is highly noticeable, and this will influence the flavor of your cup of coffee.

Want to know more about the difference between extraction and yield? This video explains it very well.

Other related questions

Does stronger coffee have more caffeine?

Stronger coffee, as said before, has more total dissolved coffee solids than weaker coffee. Amongst those coffee soluble solids is caffeine. Therefore stronger coffee should have more caffeine than a weaker one.

Is dark roast coffee stronger than medium roast coffee?

The darkness of the roast does not influence total dissolved coffee solids. It does however influence the amount of maillard compounds and caramelized sugars that are in coffee, therefore giving a more bitter coffee flavor in dark roast coffees than medium or light roasts.

What method makes the strongest coffee?

The following table describes various coffee to water brew ratios depending on the brewing method. These values are approximate, and at the end depend on personal preference.

In a general manner, you can see that espresso is the one that has the lowest coffee to water ratio, therefore the highest total dissolved coffee solids.

Espresso can be drunk alone but is also the base for other drinks like macchiato, americano and capuccino. Each of these adds other ingredients to the espresso drink like milk or water, and therefore dilute the coffee solids amongst more liquid, hence the strong flavor diminishes.

Next to espresso, Turkish coffee is very strong.

Pour over and drip methods are on the other end of the scale, using less coffee per amount of water.

What can you do if your coffee es too strong?

If you brewed a cup of coffee and the flavor is stronger than you would like, then you can fix it by adding hot water to dilute the coffee solids. It would be best to add a little of water, test it and add more water if needed.

You can fix a strong cup of coffee, however if you add too much and it is now weak there is nothing you can do to save this cup of coffee but to add more coffee solids, which would be the same as to start all over again.

With time and patience you will start to see what is your preferred brew ratio.

It is important to take notes on the amounts you have used so that you know what worked and what did not and therefore it will be clear to then make adjustments.

Also, it is better to change one variable at a time. For example, if you are increasing the amount of coffee per water, then leave the grind alone. When you have found your desired ratio try with the grind until you perfect it just right.

If you change the type of coffee you use you may have to make new adjustments.

Happy Brewing!

References

Easto, Jessica (2017). Craft Coffee: A Manual: Brewing a Better Cup at Home. Chicago. First edition.

Hoffman, J. James Hoffmann (2018). The World Atlas of Coffee: From beans to brewing - coffees explored, explained and enjoyed.

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