Coffee Extraction – Nuts & Bolts

Think of this as another version of “The Perfect Cup”. My goal with this piece is to help you understand the fundamentals of coffee brewing well enough that you can take a new coffee, or brewing method, and “Find” its full potential using this guide. Lets examine the main variables that influence the extraction of coffee at a microscopic level and this will guide our decisions in the brewing process.

A roasted coffee seed only consists of 30% solubles. The other 70% of the bean is made of insoluble fibers and carbohydrates that create the beans structure. Only 20 – 22% of the solubles are desirable, so we have to understand what’s happening and when, to avoid getting the ‘bad’ 8 – 10% soluble in our brew.

The variables:

  • Age of Coffee / Time off Roast
  • Roast Level / Bean Density
  • Grind Size
  • Water Temp
  • Water Quality
  • Dose / Brew Ratio
  • Contact Time
  • Filter Media

How can we account for this many factors??

Age of Coffee & Roast Level

Let’s start with the structure of the coffee bean. Simply, its a honeycomb of closed cells that lock up the solubles, and gases that are created during the roasting process. The age of the coffee then affects the changes that happen inside those cells. This in turn affects the interaction with the water. This is a hard one to factor in because roasting methods and green quality / age can really affect this one. Generally tho the lighter the roast the less the effect age has. A lighter roast equals a higher density, meaning that the heat from roasting has had less effect on the bean, leaving its cellular structure more intact.

Grind Size

So we grind to make these cells, and their tasty solubles, accessible to the brew water. The size of the grind determines how quickly the extraction happens. This is where a quality grinder starts to come into focus, and how uniform is the particle size.

Water Temp/Quality

Water temp. There’s probably been too much focus placed on water temp. Rather, when it’s viewed as just another factor, it can be varied within the dynamics of the other variables. It’s very likely that water quality with the correct mineral content and/or TDS is more important and one of the least considered variables in the brewing process!

Dose/Brew Ratio

Brewing ratio is one variable that most coffee professionals watch closely. Mostly because it’s easy to measure and control with a gram scale. It’s worth noting that when one, or more, of the other variables can’t be controlled that ‘the dose’ can offset those unchangeable factors.

Contact Time

Contact time is the total time of water / coffee contact, from pre-infusion thru the draw-down. This is probably affected as much by water temp / TDS and bean density as by the grind size. This becomes more apparent with high quality grinding equipment.

Filter Media

Filter media is very important as it’s the medium between the insolubles and all the great tasting things we want in the cup. It also has a big part to play in the contact time. Don’t be afraid to try different filters, or purchase filters from reputable manufactures.

Desirables

Now let’s talk a bit more about these 20 – 22% desirables. These come in many different shapes and sizes. But for simplicity let’s reduce them down to four main categories: Sugars, Acids, Melanoids & Lipids.

  • Sugars, fruit acids and caffeine are the easiest to dissolve and are responsible for light and fruity flavor notes.
  • Melanoidins that are responsible for the browning color of coffee, both in bean and liquid form.
  • Lipids are the natural fats and oils (Brewing methods that use metal filters like French Press and espresso allow lipids to pass through into the cup, producing the mouthfeel those methods are known for. The pores in paper filters are so small that they prevent most lipids from passing through.)

Thru testing with TDS meters we find that 80 – 90% of these desirables are extracted into the brew within the first minute. (Whew that’s a relief!) But it’s important to realize that for a satisfying cup, we still need some of those compounds that add fullness and body, the fats and lipids. These possibly need 3 minutes to extract. We are also lucky in that the 8 – 10% bitter compounds are the slowest to extract and spoil our efforts so far.

Final

So now how to balance this dynamic process? Reducing the unknowns helps. Achieving perfection every time likely won’t happen, but this adds satisfaction to the times we experience that ‘Oh so good’ cup. I believe with time and thinking about what’s happening at the cellular level we start to connect the dots and make sense out of the mystery of the brew… 

This is another very good article that does a good job of explaining the Nuts & Bolts of Brewing Coffee https://handground.com/grind/an-intuitive-guide-to-coffee-solubles-extraction-and-tds