Coffee strength and taste
A lot of times you will hear about coffee being strong or weak and blaming the roasting or beans type. However most of the grounds have a similar caffeine content per gram, when it comes from the same blend. In case of Arabica which is the most common one, it is roughly 1% per total mass in grams. As a rule of thumb for every 10 grams of beans or ground you should get about 100mg of caffeine. Blends of Robusta or mixed Arabica and Robusta can contain much higher amount of caffeine, that could end up to the double of Arabica.
Nevertheless the strength of coffee relies mostly on its coffee to water ratio and not just the ground itself. A brewing process can yield from 0.8% to 1.6% solubles concentration in water. That means the amount of the coffee ground that has been dissolved during brewing into the cup. So for example 1.2% means that 1.2% of your cup content is actually coffee and the rest is water. As you understand a higher percentage will produce a stronger coffee.
The following chart will help you prepare the optimum cup of coffee.
Optimum coffee to water ratio
The SCAA (Specialty Coffee Association of America) has performed a survey to evaluate the optimum coffee to water ratio. Volunteers where asked to drink various cups of coffee of several ratios and rate them. Notably the ground was made out of medium roast beans that has a medium bitterness also. Darker roasts have a stronger taste in general. Keep in mind that the survey was done with American citizens, as the Europeans prefer slightly stronger coffee.
The water amount was stable at 1.9 liters for each coffee strength, where the latter ranged from 78 to 135 grams (2.75 – 4.75 oz.). According to the results the most favorable coffee types had solubles concentration from 1.15% to 1.35%. That was the preferred amount of actual coffee in the cup.
So for instance if an 8 oz. cup (237 ml) has 1.25% of coffee solubles means that it contains 237 x 0.0125 = 2.96 grams of coffee. This would equal to 2.96 x 0.01 = 29.6 mg of caffeine which sounds too low. Because of the higher solubility of caffeine, compared to the rest of particles in ground, the actual percentage in the cup is much higher. Assuming that a typical 8 oz. cup of brewed coffee contains an average of 145mg it would be more precise to use a factor of 5. This way our 1.25% cup of coffee which is the average amount of solubles, would be composed of 2.96 x 0.05 = 148 mg of caffeine.
How to adjust coffee strength
There are two ways to change the strength and subsequently the coffee’s bitterness. The most obvious is by adjusting the water amount. Using more water you dilute the coffee further and obtain a weaker taste. Following the opposite procedure you make it stronger.
Another one method is the brewing time. The final soluble content depends also on the time spent of the hot water dripping into the ground. For the same amount of water, if the brewing time is higher you can surely get a stronger coffee. Inversely quick brewing or short brewing cycles will yield a weaker taste. There are a lot of different drip coffee makers in the market which we have reviewed extensively for your convenience.