Coffee extraction – a review of various parameters and their influence on the physicochemical character and taste of coffee. Under this title in English, a current research paper has been published, which we summarize here for you.
For the past decade, more and more research has been conducted on coffee. As Kaffeemachers, we believe that coffee is less an art but rather a craft. Whether it's roasting, brewing, pulling espressos – you can learn everything.
However, to understand what exactly happens in the process, scientific studies help us. They are pragmatic, detail-obsessed, demystifying, but for non-scientists also always somewhat cumbersome.
We are not natural scientists, but we like to dive into most coffee topics. So we thought that we would read selected papers for you and try to summarize the highlights in simpler German words.
The discussed paper for download:
The authors are:
Nancy Cordoba, Mario Fernandez-Alduenda, Fabian L. Moreno, Yolanda Ruizb
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. So, coffee extraction.
What is it really about?
The authors discuss various parameters and their influence on brewing coffee. About roasting, grinding, water quality, and so on. All of this has a significant influence on coffee extraction. They say that the flavor notes in brewed coffee are due to volatile and non-volatile components that are created during roasting.
Then the authors focus on what role 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 flavor profiles of brewed coffee.
Key findings on coffee extraction
- the more we understand what exactly happens when brewing coffee, the more we can predict what flavors will end up in the cup
- most brewing methods were developed to produce different flavors
- there are increasingly more brewing methods that are gaining acceptance, but scientific data is lacking to explain what exactly happens in each
- the methods differ primarily in the applied pressure, the water-to-coffee ratio, water quality, contact time, distribution of particle size, and temperature
- what is still missing would be a thorough explanation of mass and energy transport to explain the relationship between extraction variables and flavors
Step by step: the essence of coffee extraction
In summary, here are statements from the paper with our comments.
Although coffee extraction only takes a few minutes, it is partly responsible for a large portion of coffee quality
- and we must never forget: from harvest, through post-harvest processes, to import and roasting takes approximately +/- 5 months. And then we brew the coffee in 3 minutes and can fail right there
Coffee brewing methods differ depending on geographic, cultural, and social context, as well as of course individual preferences.
- I am always amazed on coffee trips at what you can use to make filter coffee. You really only need a medium that filters the coffee. A fun machine is the chorreador, a traditional brewing method from Costa Rica.
However, what is always the same: the direct contact between water and roasted and ground coffee, so that the water can bring the flavor into the beverage. This is followed by subjective judgment, but this depends on objective standards – if I like more body (subjective), I dose the powder amount higher (objective)
- I like this distinction between subjective and objective, as it can help us speak more neutrally about taste while also seeing 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 and water influence the taste. However, the influence of physical conditions has received even less attention in research. So it appears that there are many myths about coffee extraction
- wonderful! We humans have the habit of making things explainable. And whoever brews coffee repeatedly might wonder why the coffee was better or worse the next day. It's quite possible that the reason was different from what we assumed. The researchers talk, for example, about "permeability" and "diffusion" (p.2) as further research questions to analyze the brewing process even better. Understanding all the details helps us brew coffee even better.
On page 2, they then say that because of so many factors, it is difficult to brew high-quality coffee in a reproducible way.
- definitely. And that's why we brew the same coffee many times in our courses and pay attention to the details. We also compete in brewing championships – so we have the perfect training to always brew the same way.
How is there good coffee?
The coffee quality of a finished beverage is laid out in the green coffee. Chemical substances, also known as aroma precursors, which manifest themselves during roasting, bring the flavor into the cup.
- the aroma precursors that we can create through controlled post-harvest processes and fermentations we discussed in detail here.
These substances are transformed into volatile and non-volatile components during the roasting process. Many of them are then dissolved in the extraction, depending on particle size, among other things.
An adjustment of any one of the parameters naturally means that the beverage can taste different.
Methods of coffee extraction
The authors distinguish between various brewing methods.
Decoction method: (larger amount 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 individual water portions
- filter coffee
Pressure (pressure is responsible for pressing water through a coffee bed)
- Moka, espresso, French press
- Although, French press is a combination of steeping – the pressure plays no role 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 from the 1950s and has changed little. The authors see it as no longer up to date because it does not address flavors and includes only few of today's existing brewing methods. It essentially reduces brewing to extraction and strength.
Further tools are needed that analyze flavor, not just dissolved solids
- and of course, it also requires the human, the sensorily trained palate, with which the taste can be understood.
- in the end, it's about enjoyment – and so far humans do the best work here in distinguishing what is tasty and what is less tasty.
pH and acidity
pH: number of hydrogen ion concentration
total titratable acidity measures all protons
Total acidity and pH have long been used to determine acidity in a beverage. The perceived acidity is primarily attributed to the following acids:
Acetic, malic, formic, lactic, chlorogenic, quinic acid
The relationship between pH and titratable acidity is not yet fully researched.
- but: we measure lower pH values in a coffee from Kenya than in a coffee from Brazil
- lower pH AND less perceived acidity
9 facts about coffee extraction to impress (almost) anywhere
The concentration of fats in unfiltered coffee (e.g., espresso) is higher than in filter coffees. A filter retains many fats.
Fats play an important role in flavor formation because they create an emulsion that can store and transport aromas. They also improve the texture of the beverage.
CGA (chlorogenic acids) are relatively abundant in the beverage and are responsible for antioxidants, are anti-inflammatory, anticarcinogenic, and antimutagen.
A maximum of 30% of bitterness comes from caffeine and trigonelline.
Sugars, organic acids, caffeine are extracted super efficiently in the first seconds, and more than 90%.
In filter coffee – in the first 2 minutes, approximately 65-75% of the available flavor potential dissolves.
In cold brew: 400 minutes (approximately 7 hours) are enough for us to be in balance.
At higher temperatures, the kinetic energy of water molecules is higher. More mobility increases the possibility of dissolving components from the coffee bed.
During brewing, coffee beans grow by 20-23% after being wet for 10-15 minutes.
- We have noted more on the topic extraction and strength here.
- A basic requirement for extraction is the grinding of the coffee. This article covers it in more detail than any other on the net.
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