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I like strong coffee. Strong coffee has enough caffeine, has a great mouthfeel and tends to compliment the rich complexity of coffee’s flavor. The question, at least from the perspective of repeatability, is how to get your coffee to taste this way consistently without it being the avoidable, bitter slurry that more resembles sludge and causes your brew to taste… undesirable. 

This blog is going to cover the best way to consistently brew strong, delicious coffee that isn’t overly bitter. Bonus: We will also cover the science behind coffee extraction.

Recipe Is Key

The best way to get consistently strong coffee is to use a recipe. The best way to think of recipes for coffee is in ratios and most coffee people use a ratio of water weight to coffee weight in mass like grams or ounces. 

A good starting point for strong coffee is a 15:1 ratio. This means that you are going to use 15 parts water per each one part coffee by mass. By mass means using a scale, by volume would be using scoops like many baking recipes in, say, The Joy of Cooking. 

Use a Scale, Or Do Some Conversions

The “by mass” part is crucial because coffee is significantly lighter than water by volume, meaning that if you added one tablespoon of whole bean coffee to your grinder you would need to use significantly less than 15 tablespoons of water to keep close to a 15:1 ratio. 

The easiest way to achieve “by mass” equivalency is to use a scale to measure everything and make pour over coffee where your cup, brewer and coffee can easily fit on said scale. 

If you don’t have a scale or simply refuse to add more gadgets to your kitchen, we can approximate things: For a typical cup of coffee of about 10 brewed ounces by volume, you would need 3-4 tablespoons of ground coffee. 

Great, So I Have a Recipe, That's It?

The second factor in getting your cup to be strong is that you need to do a pretty good job extracting the coffee from the grounds. This means you need to do the following reasonably well:

1. Grind your coffee evenly
   Burr grinders (as opposed to blade grinders) do a great job of this. For drip coffee use kosher salt as your reference point for the texture and size of the grounds when you are done grinding.
2. Use hot water
   Your water needs to be consistently hot, ideally around 200 degrees. 
3. Use a technique, or a brewer, that can give you an even extraction
   Coffee becomes “strong” because hot water washes the coffee solids away from the grounds into your cup. If you just dump the water in, a lot of water is going to rush around your ground coffee, causing your cup to be poorly extracted.

There are a lot of ways to get an even extraction, but let's just say this: simply, your brew method should add water slowly or in pulses and evenly enough that your grounds are uniform and relatively flat by the end of your brew. You should also take at least 1:30 seconds for a single cup.

It also shouldn’t take much more than 6 minutes for any brew method if you want it to taste really good (except for cold brew, but that's another post).

Awesome, So I Can Just Do Some Conversions On My Favorite Brewer and Get a Good, Strong Cup?

This is the biggest bummer of this whole blog. Many brewers are simply not built to produce strong coffee consistently. Even some of the most expensive and top rated brewers on the market come with a giant thermal carafe that can hold 30-60 ounces (by mass) of water. Doing some math, that same brew basket can’t really hold 2-4 ounces (by mass) of ground coffee without overflowing and making a mess. 

Pour Over Methods Are Great for Recipe Consistency

Single cup pour-overs can be brewed crazy strong, 10:1 or more and you still get a pretty even extraction. For multiple cups, we really like a big plastic drip cone like the Kalita 103. You can easily pack 2-3 ounces of coffee into this and pour a giant thermos of coffee. 

How To Calibrate Your Home Coffee Consistently

For home coffee makers, we recommend first seeing how much coffee your brew basket can hold if it's about 40% full, a bit less than half way. Then multiply this amount by 15 or so for the number of ounces or grams of water that you should use. In most cases it won’t be close to a full pot.

The Science

Coffee scientists developed a device for measuring the strength of coffee using a coffee refractometer, which uses a beam of light, passed through the brewed coffee to give a close approximation of the amount of coffee stuff dissolved into water. 

As an aside, before they developed the coffee refractometer, scientists would take the coffee grounds from a brewed batch and dehydrate them in the oven and measure the difference in weight, or mass of the brewed amount after brewing. This difference was how much of the coffee grounds dissolved into water and ended up passing into your cup. 

The measure that you hear often when objectively discussing coffee strength is TDS or Total Dissolved Solids %. This means: how much coffee is in your water. A strong cup of coffee will typically have a TDS of around 1.2 or more. 

Interestingly, in some of our anecdotal experiments, novice tasters can perceive a difference in coffee strength of .1% TDS. Many people like coffee weaker than 1.2% but most like it between 1.2% and 1.5%.

Extraction

The above section references techniques such as grind size, water temperature and brew method, but coffee typically tastes best when around 20% of the extractable solids end up in the cup. This means that if you use 20 grams of ground coffee, about 4 grams end up dissolved in your cup. One of the reasons that brewed coffee recipes end up in a range of 12:1 to 18:1 is that the amount of liquid tends to dissolve the brewed coffee effectively without pulling out too many bitter, dry, hollow flavors that come when you try to extract more. 

I Want Strong Coffee, Can’t I Just Grind Finer?

Unfortunately no. Two things happen when we grind finer than kosher salt. First, the coffee tends to extract unevenly. The fineness of the grind tends to cause the water not to saturate evenly, causing the overall extraction to be inefficient. Furthermore, the coffee that does tend to get enough water will over extract, causing a lot of bitterness in the cup. 

What If I Load Up the Brew and Use a Tiny Amount of Water, Can I Make It Super Strong?

Yes and no. Yes, you will get a really strong cup. Unfortunately, similar to the example above, your extraction will be inefficient (not enough water to wash the good stuff off) and the remaining brew will be more acidic (acids are the first things to extract). 

There are two notable exceptions to the above rule of thumb: espresso and aeropress, both of which use pressure to extract the coffee with much less water. Pressure equalizes the extraction on the fine grinds allowing for efficient brews with far less water.