From an extraction perspective, the quality of a good espresso shot first depends on the selection of the coffee beans, followed by the flavor and concentration (strength) of the espresso concentrate, and finally details like the proportions of added ingredients, temperature, and so on. Among these steps, preparing the espresso concentrate often perplexes home baristas due to the various unexpected issues that can arise.
For example, when the espresso is too weak, resulting in a coffee that tastes bland, "watery," or noticeably lacks aroma. Facing this situation, some people have asked me this: Without changing the grind size, to increase the coffee concentration, should I extract more liquid, or should I extend the extraction time?
What Factors Affect Espresso Concentration?
Let's first observe the complete espresso extraction process. I pulled a shot today using my classic espresso blend's dialed-in parameters (20g dose, 30 seconds extraction time, 40g yield). I then used three cups to collect the espresso in 10-second intervals: the first, middle, and final segments, and tasted all three portions sequentially.
The liquid's color visibly transitioned from dark to light, and the texture went from viscous to thin.
The first cup had the highest aroma and concentration, a heavy caramel fragrance, and was slightly salty.
The second cup had a moderate body, nutty notes, and was relatively balanced.
The third cup had the lowest concentration, and the crema started to turn whitish.
This observation clearly shows that the concentration of the espresso liquid gradually decreases as the extraction volume increases, the aroma fades from intense to mild, and the mouthfeel changes from thick to thin.
Can I Extract More Coffee?
Theoretically, about 30% of the coffee bean's weight consists of substances that can be dissolved and carried out by water. Within this 30%, one part consists of desirable, delicious compounds, while the other part contains unpleasant, negative flavors. The Golden Ratio generally suggests that an extraction yield between 18% and 22% results in the most desirable dissolved aromatic substances.
As observed above, when the crema starts to turn completely white from yellow, it essentially signals that most of the good flavor compounds have been released, and we need to stop the extraction. If we continue to let hot water rinse through the coffee bed, the remaining negative flavor compounds, such as woody flavors and bitterness, will drop into the cup with the liquid. Therefore, just like with pour-over, making a delicious espresso requires properly managing the extraction yield—getting the good flavor compounds while minimizing the negative mouthfeel caused by over-extraction.
Unlike pour-over coffee, the volume of water dispensed by an espresso machine is hard to measure directly. Thus, we are more accustomed to using the "Brew Ratio" (Dose-to-Yield Ratio) as the main parameter for managing espresso extraction.
The brew ratio depends on two factors: the weight of the coffee grounds (dose) and the weight of the extracted liquid (yield). Generally, the industry-recommended brew ratio is between 1:1.5 and 1:2.5, with 1:2 being the most common. For instance, when beginners make their first espresso, I always suggest starting with a 1:2 ratio, then adjusting up or down based on their needs. This is because a shot made at this ratio usually has a sufficiently high concentration without sacrificing the expected coffee flavor.
I once conducted a simple experiment: While keeping parameters like water temperature ($94^\circ\text{C}$), pressure ($10$ bar), grind size (Galileo Q18 setting 2), and dose (20g) unchanged, I sequentially pulled three shots with different yields: 40g, 46g, and 55g, corresponding to ratios of 1:2, 1:2.3, and 1:2.75. I then tested the concentration of each cup and tasted them.
The data analysis showed that the more coffee was extracted, the lower the concentration became, and the coffee's flavor also started to deteriorate as the liquid volume increased, exhibiting signs of over-extraction. Combining this with the principles of espresso extraction, I found that when the grind size and dose are constant, an increased yield (extended time) means more hot water passes through the coffee grounds, extracting more soluble substances, thus resulting in a higher extraction yield. At the same time, more water means the coffee is more diluted, so the concentration is actually lower.
What Should I Do to Make My Coffee Stronger?
1. For Medium-Dark Roasts (Focus on Concentration)
When using medium-dark roasted coffee beans, the aromatic compounds are typically concentrated in the first and middle segments, and the final segment often "dilutes" the shot. To boost the coffee's concentration, I recommend a high-concentration, low-yield method where you cut the final segment, turning it into a Ristretto (a concentrated, shorter shot).
Taking a 20g coffee dose as an example: the original 1:2 ratio requires extracting 40g. The adjusted plan of 1:1.5 requires extracting 30g. This will result in a bolder coffee flavor and a more substantial mouthfeel.
2. For Fruity SOEs or Light-Medium Blends (Focus on Flavor Release)
If your coffee beans are a fruity Single Origin Espresso (SOE) or a light-to-medium roast blend that is generally more acidic and lighter in aroma, and you want the coffee to exhibit a high concentration, you can appropriately extend the extraction time to increase the extraction yield.
For instance, when I make a flat white using the "basic formula" for a Yirgacheffe SOE, the overall coffee flavor can be weak, sometimes even completely masked by the milk. In this case, I will increase the dose by 0.5g to extend the extraction time to 33–35 seconds. This allows more flavor compounds to be released, giving the milk beverage a richer fruity aroma.