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The Perfect Espresso Extraction

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Two cups with espresso being poured into them. This image sits at the top of Bean Merchants blog on getting the perfect espresso extraction

Today we’re going to talk about the perfect extraction on your espresso machine. This means getting the balance just right, neither over extracted and bitter tasting, or under extracted and sour tasting.

The rules we’re going to talk about today apply to all methods of brewing coffee, but this post will specifically relate to espresso extraction.

Grinding is important

The grind size of your beans is one of the biggest influencers in extraction of any type of coffee. Grinding the beans fresh yourself, and adjusting the grind size manually will ensure a fantastic cup of coffee. A great, electric, well maintained burr grinder will ensure that you make great cups of coffee every time. We recommend a Eureka Mignon Oro. This is a top of the line burr grinder with 0 retention. It allows you to adjust the burrs so that they touch, which means you can go right down to turkish grind if need be. Your grinds will be consistent (all the same size) and you won’t lose grams of coffee inside the grinder each time you grind.

Grind size is important for espresso coffee because the size of the grind affects the rate at which water flows through the coffee grounds. A finer grind will result in a slower flow rate and a stronger, more concentrated espresso shot, while a coarser grind will result in a faster flow rate and a weaker, less concentrated shot. Additionally, the grind size must be consistent in order to ensure a consistent extraction and a well-balanced flavor in the final cup.

What is extraction?

In coffee preparation, “extraction” refers to the process by which the soluble compounds in the coffee grounds are dissolved into the water to create the final beverage. The soluble compounds that are extracted include caffeine, acids, sugars, and other flavourful compounds that give coffee its unique taste and aroma. The ideal extraction is one in which the right balance of compounds is extracted from the coffee grounds to create a balanced, flavourful cup of coffee. Factors that affect extraction include grind size, water temperature, and brewing time.

Different brewing methods extract coffee in different ways. Espresso machines form a dense puck of finely ground coffee grinds and force water through it at high pressure. A plunger will enable coarsely ground coffee grinds to be immersed in water for a length of time. Any way you extract coffee will have different variables to control, and different outcomes. Different brew methods will also suit different types of coffee better.

Over Extracted Coffee

Over-extracted coffee is a term used to describe coffee that has been brewed with too much contact time with the water, resulting in a bitter and overly strong cup of coffee. This occurs when the water is in contact with the coffee grounds for too long or when the grind is too fine. The over-extracted coffee will have a dark brown color, and a strong bitter taste, similar to that of dark chocolate or unsweetened cocoa. This is because during the over-extraction, the water dissolved a higher amount of bitter compounds from the coffee beans.

You will know you have over extracted your coffee by a few key points. 

  1. The water takes a long time to come out of the machine or doesn’t come out at all. 
  2. The flow out of the group head is slow, thin and dark. 
  3. The coffee in the cup tastes bitter. 

In an espresso machine there are a few reasons the water can take too long to make its way through the puck: You could have overloaded your basket, in which case the water has much more coffee to make its way through, and is therefore slower. You could also be grinding your coffee too fine; in this case there would be a lot more surface area in your coffee grinds, and the water will take much longer to get through them and sometimes they can even form a sand, and the water can’t make it through at all.

Under extracted coffee: 

Under-extracted coffee is a term used to describe coffee that has been extracted for too short a time, resulting in a weak, sour, or salty taste. This occurs when the water is in contact with the coffee grounds for too little time, or when the grind is too coarse. Under-extraction can also happen if the water temperature is too low or if the brewing method does not allow for adequate contact time between the water and the coffee grounds. The under-extracted coffee will have a lighter brown color and a sour taste, similar to that of unripe fruit. The under-extraction means that not enough soluble compounds have been extracted from the coffee grounds, resulting in a less flavorful and less balanced cup.

You will know you have under extracted your coffee by observing a few key points.

  1. The water is very fast coming out of the machine.
  2. The flow out of the group head is fast and a light brown or even a clear colour. 
  3. The coffee in the cup tastes salty. 

In an espresso machine there are a few reasons why the water can get through the puck too easily: You could have under dosed your basket, which means there isn’t as much resistance and the water can move the grinds around inside the portafilter. This allows channeling to occur, and the water to make its way through the beans without extracting the necessary flavours. You could also be extracting your coffee too course, which means there is not as much surface area, and the water can fit through the gaps between the coffee grinds (think water through sand vs water through rocks).

The Perfect Extraction: 

Achieving the perfect extraction with an espresso machine requires a combination of factors to be dialed in correctly.

  1. Grind size: The grind size should be fine enough to create enough resistance to the flow of water, but not so fine that it causes a clog or slow flow.
  2. Tamping: Tamping is the process of compacting the coffee grounds in the portafilter. Tamping ensures that the water is distributed evenly across the coffee bed and that the extraction is consistent.
  3. Water temperature: The water temperature should be between 190-205°F (88-96°C) to extract the coffee properly.
  4. Brew time: The brew time should be around 25-30 seconds for a single shot of espresso. This allows for an appropriate amount of time for the water to extract the coffee’s flavors.
  5. Pressure: The pressure should be between 8-10 bars, this ensures that the coffee is extracted correctly.

By properly adjusting these factors, you can achieve a balanced and flavorful espresso shot with a nice crema on top, which is the hallmark of the perfect extraction. Usually as a rule of thumb you’re aiming to get double the grams of coffee out that you put grinds into the portafilter. So for example, if you put 18 grams of coffee grinds into the portafilter basket, you’d be aiming to get 36 grams of coffee out into your cup. The perfect extraction for this ratio (1:2) is around 25 seconds. Any more than that and you’re venturing into over extracted territory and you’re going to have bitter notes hanging around. Any less than that and you’re heading into under extracted territory and are going to find sour tastes in your coffee.

You will know that you have the perfect extraction when:

  1. Your ratio of 1:2 grams of coffee comes out in approximately 25 seconds
  2. The taste in your cup is neither bitter nor salty, and you can taste the nuances of the beans.

This will vary from coffee to coffee, so it’s important that you know your beans. 



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