A Guide to Understanding How Coffee Extraction Works
5th July 2019
The coffee extraction process is an art form in itself. It is not just simply the process of dissolving coffee grounds with hot water. It requires dedication and skill to get it right. There are many factors to consider in the process of coffee extraction from the ratio of water to coffee, the precision of your grind, the roast of the coffee, the temperature of the water and the amount of time the water is in contact with your coffee.
Extracting Soluble Compounds
Brewing coffee is the process of extracting the soluble material in roasted and ground coffee. As the coffee is brewed in hot water, hundreds of compounds are extracted from the coffee beans, hence the creation of brewed coffee. Extracted coffee usually contains water-soluble compounds such as caffeine, acids, lipids and fats, sugars and carbohydrates.
The solubility of the coffee can be affected by a number of factors, from the coffee’s genetic characteristics, to grind size, water mineral content, roast degree and methods of brewing. There are different brew methods to consider for each type of coffee. You can do this with a process called “dialing in” the coffee and making adjustments to dose or grind settings as you go along, to affect the flavour.
The Many Brewing Methods
1. Brewing By Immersion
This process involves fully submerging your coffee grounds in water. The water then extracts the coffee over time and is the most common brewing method. An example of this method is the French press and usually takes no longer than 4 to 5 minutes. Most immersion brews will also require filtration. French presses use a metal filter that serves to remove coffee grounds and any unwanted particles from the final brew. Extraction slows down as the immersion time continues due to the rate of coffee solids dissolving into water.
2. Brewing By Infusion
All common drip brewing methods use infusion and can be more efficient at extracting coffee solubles than the immersion method because it provides a constant supply of fresh water. Infusion brewing involves water constantly flowing through a bed of ground coffee and filter.
3. The Espresso Method
Espresso is also a form of infusion and contributes to the coffee brewing process. Espresso is a traditional Italian beverage that is extracted under pressure under the right conditions and using proper equipment, including a manual or automatic grinder and commercial coffee machine. The serving size of an espresso is usually between 20 to 40ml and is much more concentrated than regular drip coffee. A finer grind along with pressurised water enables a quick and efficient brew within 20- 30 seconds.
Brew Ratios and How They Work
A coffee brew ratio is the ratio of ground coffee to water used during the brewing process. If you are looking to scale up and make enough brew for a group of people, then it is important to know your brew ratios inside out, to get the extraction process right.
The standard brew ratio for drip coffee is 1:16 – for every gram of ground coffee, you add 16 grams of water. Most brew ratios tend to lie between 1:15 to 1:18. When it comes to making espresso shots on their own, due to quick rates of extraction the ratio is usually closer to 1:2. If you are using less water to increase the strength of your coffee, it can become difficult for the water to extract out all the desired flavours. Always find a ratio that produces the strength of coffee you enjoy before working on improving your extraction.
Measuring both your coffee and brew water is crucial if you want to pour your ratios correctly. It is recommended to use a digital scale when it comes to measuring out your ratios. With brew ratio you can determine your extraction percentage and tells you how efficiently the dry ground coffee has dissolved into the water as you drink the coffee.
What is Brew Manipulation?
Brew manipulation is the process of altering the taste of your coffee and affecting the way your coffee is brewed. There are various techniques you can use to improve flavour, so let’s check them out:
This involves stirring or disturbing the coffee grounds during the brewing process, which will increase the rate of extraction and is useful for immersion. It helps to break up the crust and build-up of wet coffee grounds that float to the surface when making French Press coffee.
Bypassing is adding water to already brewed coffee and is a simple way of diluting your cup of coffee. If you like the flavour of strong coffee but not so keen on the viscous mouthfeel then just add extra water to reduce the brew strength. This has no affect on your brew ratio or extraction percentage.
Pulsing means adding a small measurement of water at a time when infusion brewing, rather than creating a constant stream, to allow the coffee grounds in the filter bed to settle. This process helps to improve the consistency and efficiency of extraction.
This is the process of introducing enough water to saturate your coffee grounds and is used in infusion brewing. This can help improve the overall quality of the extraction for most drip brew techniques and is also referred to as the “bloom.”
Understanding Under and Over Extraction
There are three types of extraction – under extraction, over extraction and balanced extraction. Under extracted coffee is the result of a coffee that hasn’t yet reached a sweet spot of balanced and flavour where the water hasn’t succeeded in pulling all the bitter compounds, acids and oils out of the coffee, while an over extracted coffee is often too bitter to taste. A balanced extraction, on the other hand, is rich with an array of flavours, is aromatic and crisp with a balanced acidity and even has a hint of low-noted bitterness. In other words, it is every coffee lover’s dream.
The Signs of Over Extracted Coffee
It is also possible to over extract your coffee, when it comes to brewing. Here are some of the main signs to determine whether your coffee has been over extracted.
1. Bitter Taste
Over extracted coffee often tastes unpleasantly bitter resulting from loss of those essential acids and compounds during the extraction process.
Over extracted coffee is like tasting unsweetened black tea and is a result from certains chemicals that cause dryness in coffee, like polyphenols. These chemicals create a dry sensation in the mouth.
3. Hollow and Empty
An over extracted coffee will often taste lifeless, empty and without its key components. There is a lack of flavour and character and is a less desirable experience.
The Signs of Under Extracted Coffee
Here are some signs to watch out for when it comes to knowing whether or not you have an under extracted coffee.
1. Overpowering Sourness
The acids in coffee when balanced, bring life to coffee flavours, creating a huge variety of flavour combinations, from strawberry, orange, chocolate or even apple. If your coffee, on the other hand, tastes sour, overly tangy and has a biting sharpness then it has been under extracted.
2. Thin Flavour
Most of the sugars and oils in a balanced extracted coffee, is left in coffee grounds instead of being pulled into the water during the extraction process with under extracted coffee. This consequently, leads to a coffee that is unpleasant and sour tasting, with a lack of stand out flavour.
Coffee that is under extracted can have salty flavours that can be tasted along with the other, sour flavour profiles. This is another sign of an under extracted coffee.
The Signs of a Balanced Extraction
A well balanced coffee is something to aim towards during the extraction process. Here are some signs to spot when you know you have made a perfectly extracted coffee.
1. Sweet and Ripe
With a well extracted coffee, the acidity is balanced and positive with just the right amount of sweetness and ripeness. The coffee is so sweet you will be able to smell the aroma.
2. Complex Acidity
The acidity is fine, complex and definable and will remind you of a specific fruit or type of wine. If the acidity is so intense you can pinpoint a variety of fruity flavours then you have succeeded.
So there you have it, everything you need to know about the types of extraction methods, signs of under and over extracted coffee and how extraction works.
Dialing in Your Coffee
This is the process of getting the extraction process right. Once you have a target brew to water ratio you can adjust your grind to get the perfect, balanced extraction we have described above. The easiest way to do this is to adjust your grind setting and ensure your tamp level is not causing any channelling. Dialing in your coffee can have two effects:
- Any small particles will slow down the flow of water through the coffee giving it more time to work on those sweeter flavour profiles.
- The small particles will have more surface area exposed making it easier for water to enter the coffee.
If your espresso shots taste bland or bitter, you will want to extract less from your coffee by adjusting your grind settings to make it coarser.
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