The extraction of your new single origin espresso is off: what do you do? Adjust the dose? Grind size? Water temperature? Or perhaps it’s about pressure, water composition, or something else altogether. 

Espresso extraction is key to delicious coffees, and for coffee shops, satisfied customers and a good turnover. However, troubleshooting espresso extraction and creating new espresso recipes can be tricky. 

I spoke with Peter Garcia, Managing Director of VA Machinery, to find out the different variables that contribute to espresso flavour. He’s overseeing The Victoria Arduino Experience at Caffè Culture 2019 in London this 28th–29th October (register before the event for a free trade pass), in which attendees will compete for prizes by deducing the temperature at which coffees were brewed, the water type that was used, the speed the beans were ground at, and more. Who better to tell me about how all these factors affect extraction? 

Lee este artículo en español Cómo Ajustar la Extracción Del Espresso y Crear Nuevas Recetas

Pulling an espresso shot. Credit: VA Machinery

How to Create a New Espresso Recipe

“When approaching a new coffee, it is always good to start with a base recipe that is an easy starting point,” Peter says. “This could be 18 g of dry coffee, 36 g of beverage extracted at 9 bar in 30 seconds.” 

You could choose to ask the roastery or coffee shop where you bought the coffee for their recommendation. However, Peter stresses that you should treat this as a starting point. He tells me, “If you speak to any coffee roaster or barista, they will give you a recipe for where their coffee tastes best. This will be dependent on the equipment used, the water quality, their own personal preference, and all of the factors above which affect extraction and flavour.”

Once you have your starting point, it’s time to begin experimenting. Make sure to do so in a logical and controlled way, however, or else it might take you longer to find the ideal recipe. In turn, this adds up to wasted coffee and wasted time. 

“Taste the results, and then change one variable at a time,” Peter tells me. “If the coffee tastes sour and under-extracted, you could lower the dose while keeping the same beverage yield, or you could lengthen the yield while keeping the original dry dose.”

Think about how this coffee is going to be drunk, too. There is no point just tasting it as an espresso if it will be mainly served as a cappuccino. “This is a big consideration, as in most cafés milk accounts for 75–90% of espresso-based drinks,” Peter tells me. “A highly extracted but low TDS espresso may taste amazing by itself, but add milk and all of the complexity disappears, so it is worthwhile keeping this in mind.

“If you are offering a range of single origin coffees which are ideally drunk black, playing around with water temperature and ideal recipes can become more fun.”

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A barista pours latte art. 

Which Variables Affect Espresso Extraction?

There is a long list of variables that affect espresso extraction. Let’s look at some of the main ones and Peter’s tips for handling them.

Dosing

Dosing is the amount of ground coffee that goes into your portafilter. Peter says that this affects how strong your coffee is – in other words, it’s about how many total dissolved solids (TDS) from the ground coffee wind up in your espresso. 

When pulling an espresso, most tend to aim for a beverage strength or TDS value of 7–12% and ideally 18–22% extraction. This is widely considered to be optimal extraction: the highest level of extraction at which coffee still tastes good. 

Don’t make the mistake of thinking that a higher number is always better, though. It depends on the flavours you are trying to pull out from your coffee.

“A higher TDS will normally result in an espresso with a heavier body and mouthfeel, and more concentrated flavours,” Peter tells me.

“Alternatively, by utilising a low dose and a higher beverage yield, you can have an espresso which is well extracted but with a low TDS.” This tends to work well when you want to highlight characteristics such as sweetness and acidity, sometimes at the expense of body and mouthfeel.

The Victoria Arduino Black Eagle. Credit: VA Machinery

Water Temperature

“Certain volatile aromatics and flavours are extracted at different temperatures,” Peter explains. “For a darker roasted espresso, we might use a lower temperature to make sure we do not extract any of the harsh flavours which can be present from the roast level. Adversely, with a dense, light-medium roasted coffee, we want to maximise extraction by using a higher temperature to extract the coffee properly and bring out all of the pleasant acidity.”

Remember that not all compounds are extracted at the same speed, either. Acidic-tasting compounds will be extracted first, while the bitter ones come through last. This gives you room to play with the type of flavours you want in the cup.

Grind Size

Compounds can’t be extracted without contact between the dry coffee grounds and water. Following on from that, the greater the surface area of the ground coffee, the more contact there is. And the finer the grind, the greater the surface area.

Espresso is known for its remarkably fine grind size which enables short extraction times, but remember that you can still tweak this. Go finer for more body and sweetness (but don’t go too fine, or your beverage might end up being bitter). Go coarser for greater acidity.

The Victoria Arduino Mythos 2, featured at VA Machinery’s London Bridge showroom. Credit: VA Machinery

Pressure & Pre-Infusion

Pressure is the force exerted by the pump in an espresso machine, pushing the water through the puck. It’s often confused with flow, which is the speed at which the water passes through the pipes. While conceptually similar, there is an important difference between the two.

“Most espresso machines are pre-set to 9 bar from factory,” Peter says, “but can be adjusted to brew from anywhere between 2–16 bar, depending on the pump itself.”

This gives you the chance to adjust your espresso extraction. “A lower pressure than normal, say 5–6 bar, will result in a more gentle flow of water to the group head and coffee puck, potentially helping with a more even extraction, gentle extraction,” he continues. 

Remember that every variable is connected, though. “This would also affect the extraction percentage given in a set time, so you may need to lengthen your brew time or beverage yield to balance extraction out,” Peter warns.

One of the most common ways that baristas use pressure is by doing a pre-infusion of the ground coffee. “Soaking the coffee puck with a lower pressure before full pressure is reached… helps mitigate channelling,” Peter tells me.

Since channelling is a sign that the water is passing only through certain areas of the puck, this results in uneven extraction. Two to five seconds of low-pressure pre-infusion can significantly reduce this risk.

The Victoria Arduino Mythos 2 and the Black Eagle espresso machine. Credit: VA Machinery

Extraction Time

While it’s possible to pull a shot in 10 seconds that would fall within the ideal range of 18–22% extraction, it’s still unlikely that you would want to drink it. Remember that certain compounds extract at different rates. It’s the contact time that produces that balanced, complex flavour. For greater acidity, opt for a quicker extraction time. For increased sweetness, try pulling a slower shot.

Remember, as well, that the ideal time will also depend on your other variables. “You can reach a properly extracted espresso in a number of ways, from 15 seconds to 45 seconds, but this will be dependent on a number of other factors,” Peter says.

Water Quality

Water quality affects not just your espresso machine longevity but also the flavour of your drinks. “Too soft and the coffee can taste sharp, acidic, and lack sweetness and body,” Peter tells me. “Too hard and your espresso becomes one-dimensional and flat with a chalky taste, and lacking complexity.” 

The amount of magnesium and calcium in your water can slow down or facilitate extraction. Filtered water is often the solution to this. At the very least, you should be aware of the quality and hardness of the water you’re brewing with. 

An espresso and a latte, ready to drink. 

A poor espresso recipe can result in bitter or watery coffee. Yet get it right and you’ll be able to bring out a coffee’s sweetness, body, acidity, and more. So, pay attention to these variables. Consider how the coffee will be consumed. And take a logical, step-by-step approach to adjusting extraction.

Enjoyed this? Read How Can We Help Consumers Understand Coffee Flavour Notes?

Please note: This article has been sponsored by Caffè Culture. Caffè Culture 2019 will be held this 28th–29th October in London. Register before the event for a free trade pass and to take part in The Victoria Arduino Experience.

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