How to analyse coffee extraction

coffee extraction

UCC’s Babin Gurung explains how to measure, maximise and analyse coffee extraction with tools, techniques and your trusty palate.

In coffee, the term extraction refers to the amount of coffee solubles dissolved in water. The idea, regardless of brewing techniques, is to draw out maximum flavours from coffee without any unwanted harshness. Extraction is what takes coffee from tasting dull, sour and lack of texture, to rich, sweet, and full-bodied. Therefore, it is important to understand the variables involved in coffee extraction and use them to brew delicious coffees. But remember, there is always a limit to how much you can extract. Higher extraction doesn’t always mean better tasting coffee.

There are two main ways to measure and analyse coffee extraction:

  • Refractometer: A refractometer is a small device used to accurately measure solubles or TDS (Total Dissolved Solids) in liquid, or in this case, brewed coffee. This information can be used to calculate the extraction yield in percentage. Brewed coffee generally sits between 18 to 24 per cent extraction.
  • Tasting: A Refractometer only gives you the percentage of solubles present in your drink. It can’t measure whether the coffee is flavoursome. So, it is important to use taste as a guide to evaluate extraction and adjust your techniques to achieve the desired result.

Here are some techniques you can use to improve extraction in coffee:

  1. Pressure: Let me quickly talk about water pressure, which is what separates espresso coffee from all other styles of coffee. The high pressure from an espresso machine (electric or manual) allows solubles to be extracted even with small amount of water. A similar level of extraction isn’t possible with drip or immersion brewing without introducing a high volume of water, which can make them taste less intense. However, pressure that is too high can sometimes lead to choking and channelling of the puck, causing uneven extraction. Most commercial espresso machines are set at nine bars, which is widely accepted to produce a consistent result. On most home machines though, this level of pressure isn’t possible, so a pressurised portafilter basket may be used to replicate this effect.
  2. Water quality: Here, water quality refers to hardness (containing higher minerals) or softness (containing lower minerals). Hard water is generally preferred for brewing as the minerals and ions not only add to the flavour but also help extract more solubles from coffee. Tap water can have a wide range of mineral content depending on the area. So, water filtration is a good solution for having consistent water quality. Refer to Dr. Monika Fekete’s October 2017 article in BeanScene titled “Water hardness made easy” to learn more on the role of water quality in extraction. Similarly, various water recipes can be found online to match your coffee extraction needs.
  3. Water temperature: The higher the water temperature, the more solubles it can extract. Therefore, most espresso machines are set at 92 to 93 °C, but this can be changed to optimise extraction. Retaining heat is just as important during the brewing process and most commercial machines are designed for it. But simple techniques like keeping group handles locked inside the group head when not in use, and flushing water before loading the handle, are some effective ways of maintaining higher temperature. This is also applicable in manual brewing where pre-heating your brewer by running boiling water through it can help retain a higher temperature.
  4. Coffee beans: As discussed in my February 2022 article of BeanScene “Creating espresso recipes”, coffee beans can have wide range of density based on the variety, growing region, processing and roasting. Coffee grown at higher elevation generally are denser and break down slower during processing and roasting, making them more difficult to extract than a lower elevation coffee. Roasting has a similar effect on the beans. On darker roasted coffees, the wall structure is weaker, making them easier to extract than a lighter roast. Therefore, when working with denser or lighter coffees, it helps to lower the dose or increase yield, and increase brew temperature and grind finer to achieve longer extraction time.
  5. Pre-infusion: In previous BeanScene editions, we have talked about age of roasted coffee affecting flavour and extraction. Fresher coffee contains excess Co2 gas which can create a barrier for water to properly extract. A simple solution is to allow small amount of water to infuse and release some of the gas making it easier for the rest of water to fully extract the flavours. This is called ‘pre-wetting’ or ‘pre-infusion’ in espresso and referred to as ‘blooming’ in filter-style coffee. Some espresso machines come with this feature, but this can be done manually as well. Pre-infusion is usually done for 30 to 40 seconds depending on the roast and freshness of coffee.
  6. Agitation: Like pre-infusion, the idea behind agitating coffee is to ensure no dry spots are left, which can cause under-extraction. This method is specific to immersion and drip style coffee where the coffee, once wet, is stirred or agitated using a spoon or stick, or sometimes just by swirling the brewer itself. Aggressive agitation can lead to channelling, which can give a muddy flavour. Adopting a proper technique is essential when agitating.
  7. Grind size: Grinding coffee beans into smaller pieces means creating more surface area, allowing water to extract. So, a general rule is: finer grind equals higher extraction. Coarser grind equals lower extraction. Once again, there is a limit to how fine you can go before it starts to over-extract or cause chocking and channelling. Use extraction time as your guide to how fine your coffee is. Uniformity in grind size is equally important as having too many fines in your grind can cause some coffee to over-extract while others may not extract properly. Using precision grinders or removing fines using a coffee sieve can help with this issue.
  8. Time: Time is one of the biggest factors in extraction. The more time water is in contact with coffee, the more solubles it will be able to extract. For espresso coffee, the time ranges anywhere from 20 to 40 seconds, while for filter style coffee, it can be little longer. One good example of using time to extract flavours is ‘cold drip’, where room temperature water is used for brewing for an extended period of time. Because cold water isn’t good at extracting solubles, small droplets of water are poured over the course of 10 to 12 hours for a gentle extraction.
  9. Grind distribution: Along with having uniform grind size, equally important is uniform distribution of coffee in the group handle or in a brewer. This allows water to travel through the coffee, evenly allowing a higher extraction. One of the techniques that is quite common in espresso coffee preparation is to use your fingers to spread the coffee across the basket. In recent times, we have seen tools such as coffee distributors or pins to de-clump coffee for better grind distribution. You can take an extra step to ensure water disperses evenly through the puck by placing a metal mesh/filter paper on top of the prepared puck before loading the group handle.

All the above techniques will help you achieve higher extraction. But knowing your coffee and equipment will be a key to your success. Tasting your coffee and refining the techniques will help you take your coffee from average to amazing.

This article appears in the June 2022 edition of BeanScene. Subscribe HERE.

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