The Basics Of Coffee Extraction: Extraction is considered the most critical and least understood aspect of coffee making. All that is in coffee dissolved in water is called coffee extraction.
Everything coffee-related dissolves into the extract. And without the section, you don’t even get a cup of coffee. The concept is relatively easy to summarize but much more challenging to understand and apply.
This post will take some effort to grasp fully, as concepts and calculations may not fit in the sensory world of coffee. Therefore, you can see more Coffee Extraction from Under to Over to really feel the difference in flavor from the extraction process.
The basic theory of coffee extraction
The coffee extraction process is dissolving the flavors in coffee into the water by some method. Each extraction process requires the participation of first coffee, second water, and water. It is affected by temperature for a certain period.
Water is an excellent solvent at the molecular level because it has a polar arrangement, i.e., two hydrogen atoms with a positive (+) charge on one side and an oxygen atom with a negative (-) charge on the other that.
This makes water “super attractive” to a wide variety of molecules. It will pull apart the bonds of other molecules, causing them to dissolve in water. According to Clive Coffee, if you heat water, all its molecules will begin to rush, making it a more efficient solvent.
Therefore, when you mix coffee into hot water, the water dissolves the various flavor compounds in the coffee. But what are the molecules and compounds found in coffee?
The main ingredients in coffee extract
When extracting coffee with hot water, we can get many “things” along with water (collectively called solvents). In terms of molecular weight, the lighter flavor molecules will enter the coffee extract first. The heavier molecules will have the following four groups of substances in turn:
- Enzymatic or Fruity Acids: Coffee’s fruity, acidic taste is the lightest flavor molecule and is dissolved early in the extraction process.
Caffeine is extracted very early, so in almost all cases the caffeine extraction ratio is the same.
- Maillard’s Compounds: Ingredients due to Maillard reaction (Reaction between Carbohydrates and Protein in coffee beans) produced during roasting, popularly flavoring beans (Nutty), toasted grain (Toasted grain), malt (Malty) or smoked meat (barbecued food), or even wood.
- Browning Sugar / Caramels: The sugar and Caramel group is the product of the breakdown of carbohydrates during roasting. Extracted after sourness and easily perceived through vanilla, chocolate, or caramel flavors.
- Dry Distillates: (Should not be translated as dehydrated or distilled). This is the product of a dark roasting process in which Polyphenol molecules bind tightly to the Protein in your saliva when ingested, causing a dry, bitter taste. This is an undesirable flavor ingredient because it causes an intense, spicy sensation of smoke and ash that is very unpleasant and long-lasting – fortunately, they are extracted last.
Concentration and extraction rate
As mentioned, coffee extract is everything in coffee that has been dissolved in water by many different ways of preparing it. And when you are familiar with coffee extraction, you will encounter two key concepts: Strength (concentration) and Extraction yield (extraction rate).
Strength – Extraction concentration is the percentage (%) of the total dissolved substances in your coffee ( Total Dissolved Solids – TDS ). When we say ‘Extract concentration,’ we are talking about the flavor intensity of the coffee; you will often use words like strong, thin, heavy, or light (rich, watery, heavy, and light) to describe it. Describe this feature.
%TDS = Dissolved mass (extraction mass) ÷ Total extract mass (Brewed coffee mass)
Typically, a cup of Espresso coffee has a concentration in the range of 7 – 12%. That means that the coffee cup is 93% to 88% water; the rest is soluble compounds. For conventional brewing methods like Pour Over, the ratio is only between 1-2%, which means they contain 98.2% and 98.8% water – According to baristahustle.com.
Because a cup of Espresso can be ten times stronger than traditional drip coffee, it will significantly affect the ability to taste the natural flavors of the coffee (although coffee contains the same flavors, the taste is not the same). Yours will interpret them differently at different concentrations). At high intensity, you might think the roast is too dark – but after diluting a cup of Espresso, it’s easy to taste flavors created by the roasting process that weren’t apparent before.
The extraction ratio ( extraction Yield or solubles yield ) is the balance of the substances in coffee being water-soluble than the total volume of the original coffee.
If you take 20g of ground coffee to make Espresso, get a cup that weighs 40 grams, and with a concentration meter you see TDS = 10% (4 grams of solute dissolved in that cup), then the extraction ratio (EY) of you are 4g/20g = 20%; Whereas if you use instant coffee, the (EY) must be 99.99%.
Optimum extraction rate (dissolved coffee/total coffee weight) : 18 -22% – According to EE.Lockhart at MIT – Coffee Brewing Institute (1950)
If your coffee cup has an extraction rate of less than 18%, it means that the desired flavor components have not been exploited. The lower the extraction ratio, the more solutes at a later stage have no chance to be extracted, resulting in an unbalanced taste.
On the contrary, if the extraction rate is more than 22%( over-extraction ), it will be very dark and bitter because the undesirable and difficult to dissolve substances have also entered the coffee.
Relationship between Strength and Extraction yield
It is not a coincidence that we can know the extraction ratio (Ey) or extraction concentration (TDS) in a cup of Espresso. Usually, Baristas temporarily calculate the above numbers through the ratio chart. On the other hand, Espresso with a TDS meter (which can be measured with a Brix meter – also known as a refractometer) to determine the concentration of solutes in the coffee, then calculate the extraction rate correctly. More precise:
Extraction yield (% )= [ Brewed Coffee(g) x TDS(%) ] / Coffee Grounds(g)
With the chart above (provided by Sam Sgambellone of Coffee Kaizen, you can easily calculate EY from TDS in a cup with EBR (ratio of powdered coffee/Espresso yield). Let’s say you have a cup of Espresso). About 32g is extracted from 16g of ground coffee, your brew ratio (EBR) is 2:1, look at the chart, the 2:1 oblique line you will see with TDS = 9% (vertical axis) corresponds to EY = 18% (horizontal axis).
According to the SCA, the total amount of soluble solids in coffee should be in the range of 11.5 to 13.5 grams per liter, which corresponds to 1.15 to 1.35%.
Meaning of extraction ratio
Have you ever heard that a cup of coffee was too light, or someone said that Espresso was too strong? Based on what to conclude that coffee is strong, fair, or balanced? Every day we make conclusions about coffee taste based on this, but very little goes into its tenets.
In short, after a bunch of theories about TDS, Exy. If a cup of coffee has an extraction yield in the range of 18 – 22%, it is likely to be “standard” and “delicious.” But not for all cases. Because although the extraction yield is high or low, it is evaluated based on the extracted flavors (Arom and Flavor), not necessarily applying the formula to calculate based on Strength.
More specifically, in some cases, a “strong” cup of coffee (due to a high TDS) can be under-extracted. The typical case is to take too much coffee and then extract it in a short time; at this time, the cup of coffee can be “strong” because many soluble substances are absorbed into the water in the first stage, but in terms of the composition of the extracts, is not diverse, because many compounds are left in the later stages of extraction.
Factors affecting coffee extract
The extraction rate depends mainly on the following factors: temperature, preparation time, milled particle size, and, in a more complicated way, the preparation method.
Coffee grind & extract
If the coffee ground is fine, the total contact surface is large, so when it comes to hot water, the substances in the coffee will dissolve faster. But when the grind is too fine, the distance between the beans is tighter, so the water penetrates longer, and the coffee will be bitter ( over-extraction ).
In contrast, if the grind is coarse, and the contact surface is large, and the coffee beans will need more time to extract the substance. That’s why the French Press needs 4 to 5 minutes of soaking time because the grind size is enormous, while the Espresso machine with fine grind needs only 20-30 seconds to extract.
However, when the task is too coarse, the faster the water penetrates the coffee, the shorter the extraction time will make the coffee thinner and more acidic ( under-extraction ).
In addition, the uniform grind size ( Particle Size Distribution (PSD ) is also important because if you grind different dimensions simultaneously, the particles will be extracted differently, so it is difficult to achieve the taste. Desire.
This is just a summary of the grind of coffee in the extraction process in general, especially for Espresso; you should see technical requirements when grinding coffee for a more specific description.
Coffee brewing & extraction temperature
Temperature, or to be precise, the water temperature, has a significant effect on the ratio of solutes in the extract. According to Kingston (2015), brewing temperature should be between 91-96 o C. If the temperature is lower than 90 o C, some of the solutes constituting flavors are not extracted, resulting in a bland coffee.
Some undesirable substances, such as bitterness, will be removed if the temperature is too high. So, by adjusting the temperature, we can change the flavor of coffee extraction; you can see more brewing temperature in the Espresso technique to better understand.
Finally, extraction time will significantly affect the flavor of the coffee (especially for Espresso). The extraction time is short, the coffee will be sour, and the fruit and fruit flavors will be more pronounced (if any).
Longer coffee will be bitter. Therefore, if you want to reduce bitterness, shorten the extraction time. However, if it is too short, it will lead to a sharp sour taste – This will be better explained in the sensory science of coffee aroma.
Some other relevant factors
If for Pour-over (drip coffee), we are encouraged to have a ratio of 1:16 (according to SCA, it is 1:16 to 1:18), meaning that 15 grams of coffee will make 240 grams of water. Then, in Espresso’s case, the standard remix ratio is between 1:1 and 1:3.
Of course, this ratio depends on many factors, mainly due to the purpose of your extraction; for example, to limit bitterness, we often use a 1:1 ratio, also known as Ristretto, to indicate extracting fruity, nut scents… but leaving most of the savory, spicy. Smoky flavors – See also Espresso mixing ratios for a better understanding.
Type of water: Actually, this is not a minor issue because water makes up 94 to 98% of coffee extract, so in this whole article, we have just mentioned the “minority” part of a cup of coffee, never mind. Regarding this issue, we also have to consider the pH, alkalinity, water hardness… Therefore, you can refer to the quality of coffee-making water according to SCA standards to be effective. Maximum for coffee extraction.
- www.baristahustle.com/ – Coffee Extraction and How to Taste It /
- www.en.wikipedia.org/ – Coffee extraction
- La Ni Kingston (2015) – How to Make Coffee – The Science Behind the Bean