Does grind size really matter?

The age old debate “Does size matter?”

In the world of coffee brewing the answer is: “yes, grind size does matter”  but  “why?” you might ask.

Why grind size matters. Today, we have many varied methods to produce great coffee at home and each method has its own niche grind. For instance, the French Press uses direct immersion brewing (the coffee is in direct contact with water)  whereas a home espresso machine is a pressurized brew method needing sufficient resistance in the brew basket to create a shot of espresso. Grind size directly effects the surface contact area changing how the coffee reacts when exposed to water.

Understanding “under extraction vs over extraction”.
When extracting coffee, we first extract our acidity and fruity notes followed by sweetness and then bitterness. Getting the correct balance is the difference between an overly sour cup and excessively bitter coffee. We will break this up into two categories:

Under extraction.
We don’t extract all the flavour compounds resulting in a sour, tea like, astringent profile. In some methods, under extraction results in weak flavour. A classic example is when purchasing coffee for a french press and then using it in a filter machine. The coarse grind does not create enough resistance in the extraction process, resulting in a sour, unpleasant cup profile.

Over extraction
We extract too much flavour compounds from the coffee giving  an imbalanced cup profile: Overly bitter, muddy, no sweetness. The excessive flavour compounds distorts the sweetness and acidity profile of the coffee. Applying the same example previously used, using a filter grind coffee in a french press will result in over extraction creating a overly bitter cup profile muting acidity and sweetness resulting in a dull cup.

Hitting the sweet spot in the extraction process gives acidity, sweetness and some darker notes to balance out the bright acids. Below we have a handy guide to helping you hit the sweet spot at home.

French Press
Method: Direct Immersion Brewing
Grind: Course
Too fine: Coffee tastes overly bitter. Grounds can seep through mesh filter.
Too coarse: Slow extraction time, sour flavours. Extended brew time may extract unwanted flavours

Filter (Pour Over)
Drip brewing
Grind: Medium
Too fine: Slows down extraction, overly bitter, in extreme cases can clog paper filters
Too coarse: Fast extraction, under extracted sour flavours. Can be perceived as weak. 

Method: Pressurized brew method
Grind: Medium (Between filter and moka pot)
Too Fine: Excessive pressure on brew chamber, overly bitter. Lacking sweetness.
Too Coarse: Sour, under extracted brew. Lacking balance in flavour.

Stove Top Espresso Maker (Moka Pot)
Pressurized brew method
Grind: Fine (Not as fine as espresso)
Too fine: Slow extraction, overly bitter, lacks sweetness and acidity. Can choke the moka pot.
Too coarse: Sour, unbalanced. Coffee comes out light brown, watery

Method: Pressurized brew method
Grind: Fine
Too fine: Under extraction, concentrated. Chokes machine
Too coarse: Over extraction, sour and watery. Coffee comes out light brown, flows excessively fast. Coffee does not compact sufficiently in the portafilter.

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