The coffee extraction process

What is coffee extraction?

The extraction process involves the separation (removal) of certain substances from the ground coffee into a solvent, i.e. water. Extraction is the magic that transforms the water and roasted beans into the beloved beverage - coffee.

We can control this process, i.e. how the coffee is extracted into the water. The method of preparation, the fineness of the grind, the extraction ratio (i.e. the ratio of coffee to water), the extraction time, the temperature of the water, the composition of the water... and many other factors.

Coffee composition or what is extracted from the coffee

You have a craving for coffee. You take, for example, French Press, a kettle of hot water, freshly ground roasted coffee and start pouring the water over it. The moment thecoffee meets the water, extraction begins and from that point on the coffee starts to release these ingredients:

  • soluble solids
  • insoluble solids
  • insoluble oils
  • soluble gases

1. Insoluble solids in coffee

Solids that areinsoluble are trapped on the coffee filters ofcoffee machines and coffee brewing equipment. Those solids that pass through the filter form a certain turbidity in the resulting cup of coffee. The preparation method chosen affects the passage of insoluble solids into the final extract.

For example, coffee from an Aeropress is cleaner than coffee from the aforementioned French Press. This is because the metal filter in the French Press allows more insoluble particles to pass through than thepaper filter used by theAeropress. As a result, this difference is felt not only visually but also when tasting.

You can tell the difference between French Press and Aeropress coffee just by looking at it. The metal filter of the French Press lets more solids through when extracting the coffee. In contrast, the Aeropress with a paper filter produces a cleaner coffee.

2. Soluble solids in the coffee

Soluble solids are the most important determinants of the final taste of beverage. During extraction, they gradually dissolve into the hot water. Thefruit acid molecules are dissolved first . These bring a fruity flavour and a certain acidity to the coffee. Acidic notes in coffee are usually referred to as acidity.

Depending on the type of coffee, the processing, the roasting method and finally the preparation method, the degree of acidity varies. Sometimes it can be minimal, essentially a coffee without acidity. In any case, acidity is natural to coffee and so we must take it into account during extraction and, if necessary, fine-tune its expression during preparation with the right recipe.

Next up are the sugar molecules. The sugars in the coffee bean are caramelised by roasting. Just as when you melt sugar in a pan to make caramel by heating it, the roasting process needs to be carefully controlled. In dark roast coffee, these sugars are not caramelised but burnt. Such coffee will taste unpleasantly bitter in the final cup.

Towards the end of the extraction process, the dry distillates and Maillard compoundsare dissolved. These affect, for example, the nutty and smoky flavours in the coffee. The typical coffee bitterness, which is not astringent but lingers pleasantly in the mouth, is a sign of a properly completed extraction.

3. Insoluble oils

The oils hidden in the roasted coffee beans do not dissolve into the water, but they do leach into the water and bind to it during extraction. The water carries the coffee oils into your cup, where they are then felt as the texture of the coffeewhen you drink it. The coffee oils are more visible in the cup if you use ametal filter in the brewing process . It is these oils that create the typical crema on the surface of the espresso.

4. Soluble gases

Gases are carriers of aromas. They bring aromas to the cup that change as they cool. As with food, aroma influences the perception of taste. The aroma of coffee during preparation, i.e. the gases extracted, can induce a feeling of well-being. This psychological effect of coffee is linked to the positive experiences and memories we associate with coffee.

The principle of coffee extraction

Harmonious coffee with a full-bodied taste. This is the result of perfect extraction, which is the goal of all baristas whether professional or home. Coffee harmony means a spectrum of perfectly balanced flavours. At the same time, the fullness of coffee refers to its strong body, i.e. the feeling we have in our mouth after drinking it.

Coffee, whether it is brewing espresso or filter coffee, can feel full or empty in our mouths. It is this fullness, the strength of the coffee body, that is determined by the percentage of TDS (total dissolved solids).

As we described above, substances are extracted into the water gradually. A perfectly extracted coffee contains gradually both acidity and sweetness (caramels) and pleasantly bitter, chocolate-nutty notes. All of these flavours are in harmony in the final drink, perfectly balanced to create a complex taste experience.

About the coffee yield and extraction ratio

We can measure all the substances that are released into the coffee during the extraction period. We report the result of the measurement as a percentage of the coffee yield. The maximum yield, i.e. the maximum percentage of substances we are able to extract from the coffee, is 30%. However, such coffee is essentially undrinkable. The ideal is 20% extraction (+/- 2%). Coffee with an extraction yield below 18% will be under-extracted, while coffee with a yield above 22% will be over-extracted.

The aforementioned TDS is directly related to the extraction ratio, i.e. the ratio of coffee to water. The more coffee you use, the higher the TDS will be, which equates to more fullness of coffee flavour. The correct extraction ratio affects the harmony of coffee flavours. The flavours must be complex and not overpowering.

Extraction ratio when creating a filter coffee recipe

The most common filter ratio is 1:17 (1 gram of coffee to 17 grams of water). If we specify the volume of water in millilitres to specify the basic ratio, we usually use 6 grams of coffee per 100ml of water. With these figures, we are talking about the filtration ratio used in the preparation of filter coffee.

Ideal espresso extraction

When making espresso , the most common ratio used is 1:2 (counting the espresso from a double portafilter, effectively doppio or two espressos). This means that we use a certain amount of coffee to make espresso according to the recipe and the size of the basket in the lever and as a result, we get once as many grams of extracted coffee out of the lever. For example, from 18 grams of coffee we extract 36 grams of the resulting drink.

What can I do to influence the extraction and make the perfect coffee?

The various factors that come into play for the perfect cup of coffee during extraction include the initial choice of coffee or preparation method. If we have a packet of roasted coffee at home and a chosen preparation method - espresso machine or one of the alternative coffee preparation methods, we can control the extraction process by:

  • the extraction time and the amount of coffee or water
  • by adjusting the grinding coarseness of the coffee grinder
  • adjusting the water for coffee preparation

Coffee quantity and extraction time under control

To ensure correct extraction, measuring tools must be used. Using measurements will make the process controllable and repeatable. Only in this way can we achieve the perfect extraction, i.e. the perfect cup of coffee. Abarista scalewill give us an overview and orientation of the factors determining extraction . It is fast, accurate and shows even hundredths of a gram.

The smart barista scale has an integrated stopwatch, a timer that monitors the extraction time. The correct extraction time is determined by the substances that are gradually released. It is necessary to create the conditions for coffee preparation in such a way that all the flavour potential of the coffee can be released. Thus, not only the acidic flavours, but also the sweet, nutty and coffee-bitter flavours at the end. Simply to ensure that the flavour profile of the coffee is complete without over-extracting or under-extracting the coffee. Time can be a constant variable in coffee brewing that is easily measurable and provides consistency and orientation in coffee extraction.

Properly adjusted coffee grinding coarseness

Coffee extraction is most affected by thegrind. The fineness or coarseness of the grind must be adapted to the selected coffee brewing method. A finer grind increases the surface area - the total surface of the coffee that is exposed to water. Finer ground coffee is therefore easier to extract. This means that the substances released from the coffee into the water are extracted more quickly.

Using the famous French Press as an example, you can see that coarser ground coffee, in order to extract its full potential, takes much longer to extract in this machine than the contrasting coffee in espresso, where very finely ground coffee is used precisely for quick preparation. However, when preparing coffee usingpour-overmethods or also when preparing espresso, the extraction speed is not equal to the water flow rate through the coffee. On the contrary, the water passes faster through the coffee that is ground more coarsely.

A coarser grind, i.e. larger coffee particles, gives the coffee less resistance to flow. Water flows more easily through coarsely ground coffee than finely ground coffee. At the same time, it will not have the necessary time to extract and as a result the coffee will be weak and acidic. The challenge for every barista is to find theright grind for a particular method of coffee preparation, so that the result is a perfect extraction in a certain amount of time, and therefore a harmoniously balanced and complex cup full of flavour.

The optimum water composition for proper coffee extraction

Without water there would be no life, let alone coffee. Water is the solvent in extraction. It activates the substances stored in the roasted coffee and transfers them to the cup, where the resulting coffee contains approximately 98% water. In this cup of coffee, we then smell the substances that are extracted from the coffee in the water. But we must not forget the substances that the water has already carried with it before the extraction process begins.

Itis the minerals andother constituents of water that allow it tobe a solvent andtherefore make the extraction work. Too much of these components in the water increases the hardness of the water. Such water results in some of the extracted substances being bland and the coffee becoming bitter. Therefore, the water for making coffee should not be hard, but neither should it be soft.

It shouldalso meet a pH value of 7. It should befree of odour, impurities and chlorine. It is therefore advisable to use filtered water. As theimportance of water quality is becoming increasingly important, water filtration systems or filter kettles are available on the market and, of course, in our e-shop . These make it possible to achieve the desired water quality both in professional coffee preparation in the café and in the home. With filtered water, you also protect your coffee machine from limescale problems, which often lead to costly servicing.

Hot or cold coffee extraction?

Inaddition to the composition of the water, thetemperature ofthe water also plays a big role in extraction . Warmer water causes many substances to be extracted too quickly. On the other hand, colder water cannot dissolve certain coffee components at all or takes longer to do so. The principle of cold extraction is used in the production of the summer day coffee drink known asCold Brew. That is, cold filtered coffee. Extraction occurs bymacerating the coffee in cold water over a long period of time. Maybe even 24 hours.

Preinfusion of coffee

Extraction is also affected by the way the water reaches the coffee. That is, thepreinfusion (blooming), the dosage or the way it is watered. Then there is thepressure or turbulence of the coffee, which is caused for example by stirring, strong water flow or coffee machine shocks. Preinfusion, or blooming, is the usual start of extraction in filter coffee preparation. This pre-infusion of the coffee bed prepares the ground coffee for subsequent infusion and extraction. However, you can also use the same principle for espresso.

6 steps to perfect coffee

  • Check the coffee preparation with a scale, time, thermometer.
  • Use good quality water.
  • Choose an easily adjustable quality grinder with a consistent grind.
  • Buy properly roasted , select coffee.
  • Learn from your experience and gain valuable information from available professional sources to be able to create and adjust the recipe for your chosen coffee prepared under specific and variable conditions. As changes in humidity or air temperature will also affect the behaviour of your coffee during preparation.
  • Choose the coffee brewing method that suits you best .

Themost important thing in the end: youhave to like the coffee! We all prefer something a little different. Based on your knowledge and experience, create a coffee recipe that will give you coffee with exactly the flavours you brew it for, the flavours you love.

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