In a previous post we delved into what coffee professionals and fanatics mean when they’re talking about extraction in coffee — we discussed Total Dissolved Solids (TDS) and Extraction Yield (EY%), and opened up the floor to further conversations on the topic. Today, we’ll talk about ways to increase both TDS and EY% in your brews, and explore some of the pros and cons of achieving those increases.

The first, and probably most obvious way to increase extraction is to increase the contact between the coffee dose and the brew water. The more time that these two key ingredients spend together, the more flavour is dissolved from the former into the latter.

For immersion-style brews, where coffee and water are steeped until the brew is poured off, the brew-ee has all the control. In something like a cafetiere, a 4–5 minute brew time is typically recommended, but anyone can leave it for as little or as long as they like to suit their tastes.

For methods involving percolation (water passing through a bed of coffee, such as espresso or pour-over), controlling brew time is a little more complicated. Typically, the solution to more contact time would be to adjust the grind to be finer, thus creating a bed that gives greater resistance to the water flowing through it — think of water trying to pass through sand compared to pebbles. Conveniently, a finer grind also increases the available surface area of the coffee, making it easier for soluble material to be pulled out by the water. This then also increases the extraction of the brew.

For a pour-over brew, there are a few other tricks one can use to slow the drain time. One method is to increase the number of pours. For example, if my goal weight is 320g, I could pour all my water on at once and watch it rapidly drain through the coffee bed, or I could split it into a 50g bloom (to allow CO₂ release), followed by three 90g pours, with pauses between each pulse, prolonging the draw-down.

Agitating the coffee bed through stirring, swirling, or aggressive pouring, can cause some of the extremely fine particles of coffee to sink deeper into the bed. They can clog the filter paper in this way and lead to a ‘stalling’ of the draw down, when it takes far longer than desirable for the water to drain through and ends up an astringent (drying) or bitter brew. Therefore, it can be best to experiment a little with these tricks and figure out what works best for you; the goal is to boost extraction without compromising flavour.

Using more brew water will have a confusing effect on EY% and TDS. The solvent properties of the additional water will pull more soluble material out of the coffee dose, increasing the EY%, but the final cup will end up more diluted, with a lower TDS.

Conversely, if I want a higher TDS (giving me a more concentrated, ‘stronger’ coffee), I would use less water and expect a lower EY%. A tasty filter coffee will typically have a TDS between 1.15% and 1.45% (i.e., more than 98% water) while a delicious espresso will typically have a TDS between 8% and 12% (around 90% water) — both with an EY of around 20%.

Another trick is to increase the brewing temperature used, and so increasing the water’s solvent properties. This is why it’s typically recommended to use very hot water (96°C+) for lighter roasts, which are so dense that pulling flavour out can be quite difficult, or to use cooler water (~80°C) for very dark roasts, which are so soluble that they give up harsher flavour compounds quite easily. Using water that’s too hot can give quite sharply harsh flavour, while water that’s too cool can result in a drink that’s quite empty and a little sour.

As previously mentioned, a finer grind will increase the available surface area and so raise the level of extraction in the brew. There are caveats and downsides to pushing this too far, however.

With a cafetiere, the metal filter allows small particles through, meaning that a finer grind will result in more silt to chew on while you drink. With a pour-over brew, stalling is far more likely with finer ground coffee as there is a greater quantity of extremely fine particles. There is also a greater risk of channelling, where water passes through the coffee bed unevenly and leads to an unpleasant mix of sour and bitter flavours. This phenomenon also somewhat applies to immersion brews, as the brew water can struggle to evenly saturate the tightly packed coffee bed.

A further downside to grinding too fine, whether when brewing espresso, cafetiere, pour-over, or any other style, is that it comes with a greater likelihood that astringent particles will find their way into the end brew; esteemed coffee consultant & author Scott Rao frequently argues that there is no such thing as ‘over-extracted’ coffee (or, a too-high EY%), but instead that astringent particles are the reason that high extractions are associated with unpleasant flavour.

How then are there baristas out there achieving extremely high extractions that still taste delicious? The answer lies in the evenness or homogeneity of their extractions. This is influenced by a great number of things, including their grinder (what does a three-thousand GBP grinder offer that a £100 one lacks, anyway?), their brewing equipment (espresso machines with variable pressure, for example), and a bunch of other handy tools and tricks that together produce brews both efficiently and deliciously.

Want to know more about extracting evenly? That’s for the next post to explain...

 

Blog written by Jonas from the Wogan Brew Bar.