Coffee Extraction – A Review of Various Parameters and Their Influence on the Physiochemical Character and Flavor of Coffee. A recent research article has been published under this title, which we summarize for you here.
For the past decade, coffee research has been increasingly conducted. As coffee makers, we believe that coffee is less an art and more a craft. Whether it's roasting, brewing, or pulling espressos—you can learn everything.
However, to understand exactly what's happening, scientific studies help us. They're pragmatic, detail-oriented, demystifying, but also somewhat cumbersome for non-scientists.
We're not scientists, but we enjoy delving into most coffee-related topics. So we thought we'd read selected papers for you and try to summarize the highlights in simpler German.
The discussed paper for download:
The authors are:
Nancy Cordoba , MarioFernandez-Alduenda, Fabian L.Moreno, Yolanda.Ruiz b
Published 2020 in:
Trends in Food Science & Technology , Volume 96 , February 2020, Pages 45-60
What is it about?
How coffee flavor gets into the cup. In other words, it's about coffee extraction.
What is it really about?
The authors discuss various parameters and their influence on coffee brewing, including roasting, grinding, water quality, etc. All of these have a significant impact on coffee extraction. They argue that the flavor notes in brewed coffee are due to volatile and non-volatile components created during roasting.
The authors then focus on the role that various parameters can play in the extraction process. Brewing methods and their extraction parameters were analyzed, as well as their effect on the physicochemical properties and flavors of the brewed coffee.
Key findings on coffee extraction
- The more we understand what exactly happens when brewing coffee, the more we can predict which flavors will end up in the cup
- Most brewing methods were developed to produce different flavors
- There are more and more brewing methods that are gaining acceptance, but there is a lack of scientific data to explain what exactly happens in each case
- The methods differ primarily in the applied pressure, the water-to-coffee ratio, the water quality, the contact time, the particle size distribution, the temperature
- What is still missing is a thorough explanation of mass and energy transport to explain the relationship between extraction variables and tastes
In order: the essence of coffee extraction
In summary, statements from the paper with our comments follow.
Although coffee extraction only takes a few minutes, it is responsible for a large part of the coffee quality
- And we must never forget this: from harvest, through the post-harvest processes, to import and roasting, it usually takes around five months. And then we brew the coffee in three minutes, and we can fail.
Coffee brewing methods vary depending on geographical, cultural and social context, as well as individual preferences.
- On my coffee trips, I'm always amazed at the variety of things you can use to make filter coffee. All you need is a filtering device. A fun machine is the chorreador , a traditional brewing method from Costa Rica.
What is always the same, however, is the direct contact between water and roasted and ground coffee, so that the water can impart flavor to the drink. This is followed by the subjective assessment, which, however, is subject to objective standards – if I like more body (subjective), I add more ground coffee (objective).
- I like this distinction between subjective and objective because it can help us talk about taste in an even more neutral way while also recognizing that the recipe needs to be adjusted.
Specific extraction variables such as extraction time, water composition, temperature, pressure, particle size, and the ratio of dosage to water influence the flavor. However , the influence of physical conditions has received even less attention in research. This is why there seem to be many myths surrounding coffee extraction.
- Wonderful! We humans have a habit of making things explainable. And anyone who brews coffee repeatedly might also wonder why the coffee was better or worse the next day. It's quite possible that the reason was different from the one we assumed. Researchers are talking about "permeability" and "diffusion" (p. 2), for example, as further research questions to analyze the brewing process even more closely. Understanding all the details helps us brew coffee even better.
On page 2, they then say that due to so many factors, it is difficult to brew high-quality coffee in a reproducible manner.
- Absolutely. That's why we brew the same coffee many times in our courses, paying close attention to detail. We also participate in brewing championships—this gives us the perfect training to brew consistently.
How do you make good coffee?
The quality of a finished coffee is inherent in the raw coffee. Chemical substances, also known as aroma precursors, which only manifest during roasting, bring the flavor to the cup.
- We have discussed in detail here the aroma precursors that we can produce through controlled post-harvest processes and fermentations.
These substances are transformed into volatile and non-volatile components during the roasting process. Many of them are subsequently dissolved in the extraction, depending on the particle size, among other things.
Adjusting one of the parameters will of course result in the drink tasting different.
Methods of coffee extraction
The authors distinguish between different methods of brewing.
Decoction method : (larger quantity of coffee with longer contact between coffee particles and water)
- boiled coffee, Turkish coffee, percolator, vacuum
Infusion : hot water flows through a coffee bed, short contact time of the coffee grounds with the individual water portions
Pressure (pressure is responsible for forcing water through a coffee bed)
- Mocha, espresso , French press
- Although, French Press is a combination of letting it brew – the pressure doesn’t matter in our opinion.
TDS and extraction rate
Even though the coffee brewing chart remains widely used, its applicability is rapidly decreasing because of new coffee brewing methods.
N. Cordoba, et. al., 2020, p.49.
The Brewing Control Chart dates back to the 1950s and has changed little. The authors consider it outdated, as it doesn't address flavors and only marginally incorporates existing brewing methods. It essentially reduces brewing to extraction and strength .
More instruments are needed to analyze the taste and not just the dissolved particles
- And of course, we still need people, the sensorially trained palate, with which taste can be understood.
- At the end of the day, it's all about enjoyment – and so far, humans have done the best job of distinguishing what is delicious from what is less delicious.
pH and acidity
pH: Number of hydrogen ions Concentration
Total titratable acidity measures all protons
Total acidity and pH have long been used to determine acidity in a beverage. Perceived acidity is primarily attributed to the following acids:
Acetic, malic, formic, lactic, chlorogenic, quinic acid
The relationship between pH and titratable acidity has not yet been fully explored.
- but: we measure lower pH values in a coffee from Kenya than in a coffee from Brazil
- lower pH AND less perceptible acidity
9 facts about coffee extraction to make an impression (almost) everywhere
The fat concentration in unfiltered coffee (e.g., espresso) is higher than in filter coffee. A filter traps many of the fats.
Fats play an important role in flavor formation because they create an emulsion that can store and transport flavors. They also improve the texture of the beverage.
CGA (chlorogenic acids) are relatively high in the drink and are responsible for the antioxidants, are anti-inflammatory, anticarcinogenic, and antimutagenic.
A maximum of 30% of the bitterness comes from caffeine and trigonelline.
Sugar, organic acids, and caffeine are extracted super efficiently in the first few seconds, with more than 90% being extracted.
With filter coffee – in the first 2 minutes, approximately 65-75% of the available flavor potential is released.
In Cold Brew: 400 minutes (approx. 7 hours) are enough to achieve balance.
At higher temperatures, the kinetic energy of water molecules is higher. Greater mobility increases the ability to release components from the coffee bed.
During brewing, coffee beans grow by 20-23% after being wet for 10-15 minutes.
- We have written more about extraction and starch here .
- A fundamental prerequisite for extraction is grinding the coffee. This article covers this in more detail than any other online.
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