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Jack Merriman

Content Marketing Manager

This short video explains how the grind size of your coffee effects the extraction, flavour and strength of your espresso coffees. 

Getting the proper grind size from your grinder is one of the most important steps in creating consistently delicious espressos, having a great impact on the extraction time, flavour and and strength of the brew. Grind size directly affects the amount of surface area inside the puck of coffee, which is the main factor that determines how easily the water can pass through the coffee.

To start, we want a standardised recipe for your espresso so that we can easily control and measure the affect of grind size on the brew. We’re going to use 18 grams of coffee to brew 36 grams of liquid espresso, in 26 – 28 seconds. Having a goal extraction time helps us be consistent brew-to-brew, allowing us to achieve a full extraction of the coffee without any bitterness or harshness.

To make sure we’re achieving that 26-28 second target, we’re going to adjust our grind size to either increase or decrease resistance, to slow or speed up the extraction time when needed.

How Grind Size Affects Espresso Extraction Time

Grinding your coffee finer will create a larger number of smaller coffee particles, increasing the total amount of surface area in the coffee puck. This increases resistance therefore making it harder for water to pass through the puck – slowing down the shot and increasing the brew time. On the other side of the coin, grinding coarser will reduce the total amount of surface area, allowing the water to pass through more easily. This speeds up the shot – decreasing brew time and reducing the overall level of extraction of the coffee.

An extraction time above 28 seconds is caused by a grind that is too fine, and may lead to some harsh, dry and bitter flavours in the coffee. This is typically known as overextraction. Whereas an extraction time below 26 seconds will not give the water enough time to extract all of the flavours from the coffee, leading to some sour, weak and dull flavours – this is underextraction.

How and When to Adjust Grind Size

knowing when to adjust your grind size is simple: If your espresso shots are consistently missing the 26-28 second extraction time, you’ll need to change your grind size. If the shot is running too fast, you need more surface area, so grind finer. If the shot is too slow, the water is struggling to get through, so grind coarser. Make sure to keep all other aspects of your recipe consistent (18 gram dose, 36 gram espresso).

Your grind size is not something you can simply ‘set and forget’, as there are a large number of factors outside of your control that can affect extraction time including the freshness of the coffee and the temperature in the room. Make sure to empower your baristas with the knowledge of adjusting grind size in order to maintain control of extraction time and brew great tasting coffee day in, day out.