Coffee Extraction – A Review of Parameters and Their Influence on the Physiochemical Characteristics and Flavor of Coffee. A current research paper has been published under this title in English, which we summarize for you here.
For a decade now, there has been increasing research into coffee. As coffee makers, we believe that coffee is less an art and more a craft. Whether it's roasting, brewing, or pulling espresso shots – it can all be learned.
However, to understand exactly what happens, scientific investigations help us. These are pragmatic, detail-obsessed, demystifying, but always a bit cumbersome for non-scientists.
We are not natural scientists, but we enjoy delving into most coffee topics. So we thought we would read selected papers for you and try to summarize the highlights in simpler words in German.
The discussed paper for download:
The authors are:
NancyCordoba, MarioFernandez-Alduenda, Fabian L.Moreno, Yolanda.Ruizb
Published in 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 coffee brewing. This includes roasting, grinding, water quality, etc. All of these have a significant impact on coffee extraction. They state 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 brewed coffee.
Key Findings on Coffee Extraction
- the more we understand exactly what happens during coffee brewing, the more we can predict which flavors will end up in the cup
- most brewing methods were developed to evoke different flavors
- there are more and more brewing methods gaining acceptance, but scientific data is lacking to explain exactly what happens in each case
- the methods differ primarily in applied pressure, water-to-coffee ratio, water quality, contact time, particle size distribution, temperature
- what is still missing would be a thorough explanation of mass and energy transport to explain the relationship between extraction variables and flavors
In order: the essence of coffee extraction
Summarized below are statements from the paper with our comments.
Although coffee extraction only takes a few minutes, it is responsible for a large part of coffee quality.
- and we must never forget: from harvesting, through post-harvest processes, to import and roasting, it usually takes about +/- 5 months. And then we brew the coffee in 3 minutes and can fail there.
Coffee brewing methods differ depending on geographical, cultural, and social context, as well as individual preferences, of course.
- I am always amazed on coffee trips by what can be used to make filter coffee. You just need a medium that filters the coffee. A fun machine is the chorreador, a traditional brewing method from Costa Rica.
What always remains the same, however, is 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 a subjective assessment, which nonetheless depends on objective standards – if I like more body (subjective), I increase the amount of powder (objective)
- I like this distinction between subjective and objective, as it can help us to talk about taste more neutrally and at the same time to see that the recipe needs to be adjusted.
Specific extraction variables such as extraction time, water composition, temperature, pressure, particle size, and the ratio of dosing and water influence the taste. However, the influence of physical conditions has received less attention in research. As a result, there seem to be many myths in coffee extraction
- Wonderful! We humans tend to make things explainable. And whoever brews coffee again and again might also wonder why the coffee was better or worse the next day. It's quite possible that the reason was different from what we assumed. Researchers, for example, talk about "permeability" and "diffusion" (p.2) as further research questions to analyze the brewing process even better. So understanding all the details helps us to 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.
- Definitely. And that's why in our courses, we brew the same coffee many times and pay attention to the details. We also participate in brewing championships – that way we get the perfect training to always brew consistently.
How to make good coffee?
The coffee quality of a finished beverage is inherent in the green coffee. Chemical substances, also known as aroma precursors, which only manifest during roasting, bring the flavor into the cup.
- We have discussed in detail the aroma precursors that we can produce through controlled post-harvest processes and fermentations here.
These substances are transformed into volatile and non-volatile components during the roasting process. Many of these are then dissolved during extraction, depending on particle size, among other factors.
Adjusting any of the parameters naturally results in the beverage tasting different.
Methods of Coffee Extraction
The authors distinguish different 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 pot, Espresso, French Press
- Although, French Press is a combination of steeping – 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 back to the 1950s and has changed little. The authors consider it outdated, as it does not address flavors and incorporates little of today's existing brewing methods. It essentially reduces brewing to extraction and strength.
Further instruments are needed that analyze taste, not just dissolved particles.
- and of course, humans are still needed, the sensorially trained palate, with which taste can be understood.
- at the end of the day, it's about enjoyment – and so far, humans do the best job of distinguishing what is delicious and what is less delicious.
pH and Acidity
pH: hydrogen ion 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 acids
The connection between pH and titratable acidity has not yet been fully researched.
- but: we measure lower pH values for coffee from Kenya than for coffee from Brazil
- less pH AND less perceptible acidity
9 Facts about Coffee Extraction to Impress (almost) Anyone
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.
CGAs (Chlorogenic Acids) are relatively abundant in the beverage and are responsible for antioxidants, are anti-inflammatory, anticarcinogenic, and antimutagenic.
A maximum of 30% of bitterness comes from caffeine and trigonelline.
Sugar, organic acids, and caffeine are extracted super efficiently in the first few seconds, to more than 90%.
For filter coffee – in the first 2 minutes, approx. 65-75% of the available flavor potential is dissolved.
For Cold Brew: 400 minutes (approx. 7 hours) are sufficient to achieve a balance.
At higher temperatures, the kinetic energy of water molecules is higher. Increased mobility enhances the ability to dissolve 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 of extraction and strength here.
- A basic prerequisite for extraction is the grinding of the coffee. This article covers it more thoroughly than any other on the web.
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