Even home automatic espresso machines can produce espressos that would put many a café to shame. But, supplying coffee beans and pushing a button is not enough; you have to put in a bit more effort to get a great espresso.
Besides securing quality coffee beans – I must say that lighter roasts seem to work better here – proper water and a good machine you have to adhere to certain parameters to be able to even call your coffee an espresso and not a bucket of brown water. These parameters vary – National institute of Italian espresso has some figures, the 2020 World Barista Championship has other figures and then you have various interpretations by baristas from across the globe. In practice though it all boils down to these approximate figures:
- recommended time of extraction: 20 to 30 seconds
- ratio of ground coffee to the weight of coffee emulsion: 1:1,5 to 1:3
- pressure: 8,5 to 9,5 bars
- water temperature: 88 to 96°C, or 190.4 to 205°F
- crema: consistent
- served in a cup of 60 to 90ml, or 2 to 3oz
A home automatic coffee machine allows you to control only the speed of extraction and the weight of emulsion. We can control the weight of emulsion with a small kitchen scale and we control the speed of extraction with the grinding setting and measure it with stopwatch.
The length of extraction plays a crucial role, because not all coffee flavours dissolve at the same rate. The first things that get dissolved are acids, vegetal and floral tones. Then sugars are dissolved, providing sweetness and body to the coffee. These are followed by tones of chocolate, caramel, spice and earth. Last and slowest to dissolve are tannins. Tannins are great in wine, however in coffee they bring along astringent, tart tastes and ruin the taste of our coffee.
Fast extractions therefore extricate mainly acids from the coffee grounds, making our coffee unnecessarily (and often unpleasantly) sour and thin. Slow extractions run the risk of extracting everything all the way to the tannins, again decreasing or ruining the taste of our coffee. But do not despair – there is a window of time where the coffee grounds already release the good stuff, but not yet the bad stuff. This window is between 20 to 30 seconds of extraction, provided we follow the other quoted parameters. These values are not set in stone, though they are a good rule of thumb to follow, especially for home automatic coffee machines.
When we adjust the grinding setting we need to keep in mind a simple principle: coarser grinding produces larger grounds, which provide less resistance to the water under pressure, thus resulting in a quicker extraction. Finer grinding leads to the opposite: longer extractions. Besides grinding setting the machines typically allow us to choose the “strength” of coffee, which is derived from the amount of coffee beans the machine will grind. Less ground coffee will put up less resistance than more ground coffee, generally. It is crucial to match your grinding setting to the amount of coffee you grind. If you tinker with you grinder and later change the “strength” of your coffee, you will have to adjust your grinder once again.
Adjustment of the grinder setting is very simple:
- pour in coffee beans, refill the water tank, quickly rinse the machine system
- place a cup on a kitchen scale beneath the machine’s “head”
- Select a 30ml espresso drink, select the desired “strength” of the coffee. I would recommend selecting the strongest option possible
- Press start; once the grinder stops, begin measuring time with your stopwatch
- The machine should extract approximately 30 grams of coffee emulsion; you can of course stop it earlier if you desire a lower ratio of ground coffee to the weight of emulsion
- How long was the extraction? How is the taste? How does the crema look?
- For fast extractions (<20s), grind finer
- For slow extractions (>30s), grind coarser
- Typically, the grinding stones only move during grinding, so you need to begin preparing another coffee before adjusting the grinding setting.
Following this simple procedure you slowly edge into the 20 – 30 second extraction window. If possible, do not stop at 20 seconds, but proceed to somewhere between 25 – 30 seconds. It is possible that your machine won’t allow you to reach extractions longer than for example 15 seconds; this is perfectly fine, because home automatic machines are primarily about comfort of use and therefore have some limits. Just bear in mind that a 15 second extraction will taste better than a 10 second extraction, so every improvement counts.
As you can see, it is pretty simple, right? Good. Let’s make it more complicated.
Uneven extraction of coffee
A tamped (pressed) coffee puck presents a significant barrier to water that is trying to push through under pressure. In the ideal world water passes through the puck evenly, extracts the coffee evenly and provides a balanced, delicious coffee in the cup. This happens exactly… never.
When the resistance put up by the puck is too strong, the water will search for paths of least resistance to get through it. If the tamping (pressing) is tilted, more water will pass through the area with less coffee grounds. Even if the puck is even, from a certain point the water will find some unevenness in the puck and pass through there, creating small channels through which it sieves. This is called channelling. The unevenness may have nothing to do with you; it may have come from the grinder, from the roasting, processing, growing, the transportation or what not. Coffee supply chain is full of unevenness. If you are using a blend of different coffee varieties, know that each bean has different solubility and therefore extracts… differently.
So, let’s quickly recall the sequence of flavour extraction: acids, sugars, chocolates, spices, tannins. Every uneven extraction leads to over-extraction of the areas where more water passes and under-extraction of coffee where less water passes. Severely uneven extraction will result in a terrifying blend of acids and tannins which you may serve to your worst enemy.
What does this means for us and our automatic coffee machines? That not every prolongation of extraction is desirable. Yes, you may move from 15 seconds to 18 seconds but if you induce very uneven extraction, the taste of the cup will suffer. Therefore let us pay attention to the length of extractions but let us be guided by the taste of our coffee in the cup. Because taste is what we do it for.
If you have read through the article and came up with some questions, feel free to contact me and I will be happy to answer them.
Many thanks to Barista Hustle for their inspiring work.
If you would like to dive deeper into coffee preparation at home, take a look at my e-book Home Barista, which deals with all aspects of preparing coffee at home. You can take a look and make a purchase at Gumroad: https://gum.co/rtLln