Grind size and fresh coffee

Grind Size and Fresh Coffee Woes – An Article of Sorts by RoundBoyRoasters

It’s happened to the very best of us - we buy a coffee, grind it to what we think is acceptable, pull the shot or brew the coffee, take a sip and give a face that resembles the joker from The Dark Knight series; and die a little inside. Hence, to avoid such cosmic facial distortions, this article focuses the variable of grind size and how it influences the final cup.

The one thing to keep in mind when determining grind size is to look at it holistically. That is, the key to good coffee is to grasps the extraction bit:  Proper extraction of coffee requires using a specific quantity of coffee, ground precisely, extracted to the correct degree, controlled by the correct time and correct temperature depending on method used. In essence, coffee brewing consists of dissolving soluble flavours from the coffee grounds in water.  

The idea of extraction can be summarized into this: Extraction of coffee is the "soluble/extraction yield" – what percentages (by weight) of the grounds are dissolved in the water. Extraction also further relies on a few other variables. These include: Strength: Also known as "soluble concentration", as measured by Total Dissolved Soluble (TDS) - how concentrated or watery the coffee is. Brew ratio: The ratio of coffee grounds (mass, in grams or ounces) to water (volume, grams): how much coffee is used for a given quantity of water. These are related as follows:

Strength = Brew ratio × Extraction

In brief, ideal yield is widely agreed to be 20%±2% (18%–22%), while ideal strength (for brewed coffee) varies between 1.25%±.10%.(1.15%–1.35%) in American standards with European standards falling in the middle at 1.20%–1.45%). This is most easily achieved with a brewing ratio of 55 g/L (55 grams of coffee per 1L of water giving a 1:18 ratio) in American standards, to 60 g/L (1:16.67 ratio) in European standards, yielding approximately 14–16 grams of coffee for a standard 240 ml (8oz) cup.

Now that we understand the gist of extraction we can finally focus on grind size and how it affects extraction and helps us understand how to grind our coffee, from Fresh to Old.

Grind Size in specialty coffee is this: coffee is ground to a particular size to form resistance as water passes through it during extraction. If the grind size is too fine, there will be too much resistance and more bitter flavours will be extracted. If the grind size is too coarse there will be too little resistance and too much water will flow through it thus making the coffee acidic or weak and watery.

Grind Size

Resistance

Grind Size

Resistance

Coarse

Low

Fine

High

 

This means that rate of extraction is affected by grind size. Pour overs are an infusion method and water contact for pour overs have less time than and immersion method thus “at the end of the day you want the coffee to have enough surface area to extract before the water filters through into the cup, but not so much that they under-extract and produce a sour/bitter brew”, Perfect Daily Grind (2019).

Roast Date tells us that if the coffee is too fresh, it gives out a lot of carbon dioxide and other gases from the beans. This in turn will take up space and restrict the flow of water thus causing water resistance to be high. If the coffee is too old, there is no more gas released and therefore will have very low resistance on the water flowing within the coffee grounds.

Roast Date

Resistance

Roast Date

Resistance

Fresh

High

Old

Low

 

Therefore, if the coffee is too fresh, you can start with a medium grind size and a lower dose which helps to increase extraction by reducing water resistance of freshly roasted coffee.  As the coffee ages however, a finer grind size can be used and/or even use a coarser grind size but at a higher dose of coffee which aides in increasing water resistance and thus overall increasing overall intensity of the cup. 

In summary, in terms of grind size and fresh coffee

Roast Date

Grind Size

Dose

Outcome

Fresh

Medium/Coarse

18-21 grams

Higher extraction

Roast Date

Grind Size

Dose

Outcome

Old

Fine*/Coarse**

18*/25**

Higher intensity

 

At RoundBoyRoasters, we recommend that you try out a medium grind size on freshly roasted coffee and from there, adjust accordingly. Play around with grind settings as different grinders do churn out very different ground coffee sized, and hopefully with the help of this article today that focuses on grind size, you’ll be able to brew a flavourful cup and finally not cringe so much.   


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