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 article has been published, which we summarize here for you.
For the past decade, there has been increasingly more research on coffee. As coffee makers, we are convinced 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. These are pragmatic, detail-obsessed, demystifying, but always somewhat cumbersome for non-scientists.
We are not natural scientists, but we like to delve into most coffee topics. So we thought 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:
NancyCordoba, MarioFernandez-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 about coffee extraction.
What is it really about?
The authors discuss various parameters and their influence on brewing coffee. About roasting, grinding, water quality, etc. All of this has a significant influence on coffee extraction. They say that the flavor notes in brewed coffee can be attributed to volatile and non-volatile components that are created during roasting.
The authors then 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 insights into coffee extraction
- the more we understand what exactly happens when brewing coffee, the better 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 find acceptance, however scientific data is lacking to explain what exactly happens in each case
- the methods differ primarily in the applied pressure, the water-to-coffee ratio, water quality, contact time, the distribution of particle sizes, 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, the following statements from the paper with our comments.
Although coffee extraction only takes a few minutes, it is partly responsible for a large part of coffee quality
- and we must never forget: from harvest, through post-harvest processes, to import and roasting it usually takes around +/- 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 of course individual preferences.
- I am always amazed on coffee trips at what you can make filter coffee with. You really only need a medium that filters the coffee. A funny 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 drink. This is followed by subjective judgment, but which 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 because 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 Dosierung and water influence the taste. However, the influence of physical conditions has received even less attention in research. This is why there are apparently many myths in coffee extraction
- wonderful! We humans have the habit of making things explainable. And whoever brews coffee over and over again might wonder why the coffee tasted better or worse the next day. It's quite possible that the reason was a different one than the one we assumed. The researchers talk, for example, about "permeability" and "diffusion" (p.2) as further research questions to better analyze the brewing process. Understanding all the details thus 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.
- absolutely. And that's why we brew the same coffee many times in our courses and pay attention to the details. We also participate in brewing championships – so we have the perfect training to always brew the same.
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 only manifest themselves during roasting, bring the flavor into the cup.
- the aroma precursors that we can produce through controlled post-harvest processes and fermentations, haben 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.
Adjusting one of the parameters naturally has the consequence that the beverage can taste different.
Methods of coffee extraction
The authors distinguish 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
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 view.
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 consider it outdated because it does not address flavors and includes only few of today's existing brewing methods. It essentially reduces brewing to Extraktion and strength.
Further instruments are needed that analyze flavor, not just dissolved solids
- and of course it still takes people, the sensorially trained palate, with which the taste can be understood.
- at the end of the day it's about enjoyment – and so far people do the best job at distinguishing what tastes good and what tastes less good.
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. Perceived acidity is primarily attributed to the following acids:
Acetic, malic, formic, lactic, chlorogenic, quinic acid
The connection between pH and titratable acidity has not yet been completely researched.
- but: we measure lower pH values in a coffee from Kenya than in a coffee from Brazil
- lower pH AND lower perceptible acidity
9 facts about coffee extraction to impress (almost) everywhere
The concentration of fats in unfiltered coffee (e.g. espresso) is higher than in filter coffee. 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 present in relatively high concentrations 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 acid, caffeine are extracted super efficiently in the first seconds, and more than 90% at that.
With filter coffee – in the first 2 minutes about 65-75% of the available flavor potential dissolves.
In cold brew: 400min (approx. 7h) is enough for us to be in balance.
At higher temperatures the kinetic energy of water molecules is higher. More mobility increases the possibility of extracting components from the coffee bed.
During brewing, coffee beans grow by 20-23% after being wet for 10-15 minutes.
- More on the topic Extraktion and strength we have noted here.
- A prerequisite for extraction is the Mahlung of the coffee. This article covers it in more detail than any other on the net.
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