How Coffee Extraction Works and Why It Is So Important
21st June 2019
Whether you are an experienced barista or newbie to the coffee world, it is always important to revisit and discover the art of extracting the perfect espresso shot.
Practice makes perfect after all! By sharing these tips on how to pull the perfect espresso shot and prepare your coffee grounds, we hope to inspire you to experiment with and improve on your coffee making skills. It is extremely important to get the coffee extraction process right to truly experience the taste of freshly, grounded coffee that has been extracted to perfection. You will never taste dull, dry coffee every again!
Coffee extraction is a balance between grind size and time. It is so important to have a consistent particle size when grinding coffee beans into smaller pieces. If the grind is inconsistent it will cause some of the grounds to be over extracted, while others are under extracted. These are many factors that affect the coffee extraction process, including the type of coffee beans used, the grind size, the dose amount and tamping pressure.
The grind size determines the speed that coffee extraction happens. It is important that you always reach the recommended extraction time of 25-30 seconds for a well-extracted espresso shot. Always taste every extraction and take notes if this is your first time and you are experimenting with your coffee. With practice, you will begin to understand your coffee behaviour on slower and faster extractions.
The result should be a grind that looks and feels like caster sugar, to create the required pressure to create a tasty crema topped espresso. The grind will increase the level of pressure needed to emulsify the CO2 gases and fatty oils and acids into crema to extract espresso. A fine grind is best for when using an espresso machine, so you can build up the necessary pressure to pull an espresso shot. You will also need a fine grind because the brew time is short and you need a maximum surface area to fully extract the coffee in a short time.
Here are some of the grind size descriptions to be used as a guide:
- COARSE: Distinct, chunky pieces of coffee beans. Coarse grounds are best for French Press coffee which takes an average of 4 minutes brewing time.
- MEDIUM: A gritty texture with visible flakes, like coarse sand. This is a great grind for drip coffee or pour over brews.
- FINE: Much smoother texture, like table salt. You need a fine grind to make a great shot of espresso with a traditional espresso machine.
- EXTRA FINE: Coffee grains still barely discernible and finer than granular sugar.
Getting The Dose Right
When preparing espresso coffee the importance of dosing coffee correctly is not to be underestimated. Dosing coffee refers to grinding the correct quantity of coffee for a given filter basket when using a manual or automatic grinder. A highly specified grinder can keep the dosing chamber full at all times and automatically dose one portion of coffee into the portafilter for a single or double espresso shot of coffee and is great for high pressured environments.
There are many different volumes for portafilter baskets. A double portafilter basket usually fits between 18-25 g of ground coffee. Make sure you check this before grinding. Different coffees have different densities and is important to dose by either weight or experiment. To get the dose right, always use a scale to measure the doses. If the end result is a shot that tastes balanced and has a sweet flavour profile then it is the sign of a well-extracted shot.
Adjusting Your Grinder
To create a well-extracted coffee and manage grind dose you will need to calibrate your grinder and manage the settings. Here is guide to adjusting your grinder but remember to always check the make and model of your grinder first, as the process may be different.
- Set your grinder so when pinching the grinds you feel a very fine granularity.
- Load your stock double basket with 12 g of coffee.
- Adjust the grind until you get a shot that weighs 20-25g in 30 seconds. When timing the shot count the time between turning on the pump and seeing the first drop, also known as the dwell time.
- Repeat the procedure using a dose of 16g and a coarser grind. The setting that gets you 20-25g in 30 seconds as before will be your coarsest grind setting to be used for blander tasting coffee.
If the coffee tastes too bland, the caramels and sugars are masking the favours. Increase the dose and coarsen the grind to keep the flow the same. If the coffee tastes too bright, with more acidic flavours, keep the dose the same and make the grind finer to lower the flow rate. Make a slower shot to reduce acidity relative to the bitterness. If the coffee is too bitter, with too much bright flavours in lighter roasts, like the taste of wood, or toast, or dark bitter flavours like tobacco and clove, keep the dose the same and make the grind coarser.
What Are Total Dissolved Solids?
Extraction and TDS are the two ratios that define coffee brewing. TDS is the ratio of solubles to water in a cup which are released during extraction to determine the flavour intensity. It is generally considered that 1.15% to 1.35% is an optimal ratio in the coffee extraction process. Increasing the amount of TDS will produce a stronger flavour but turning it up too high may cause some flavours to overpower the others completely.
The dissolved solids of coffee included chlorogenic acids, caffeine and organic acids like citric, malic and lactic acids. They are compounds that make up a coffee’s body, aroma and flavour and comprise a coffee’s TDS measurement. More dissolved solids means a more concentrated and stronger brew.
TDS reflects the level of extraction of the coffee, as well as how many dissolved solids there are in the water, The most common way to measure the amount of TDS is to use a refractometer which measures the degree to which light is refracted by the liquid. TDS provides easy to analyse data that can help roasters and baristas measure and control extraction. It helps improve the taste and consistency of espresso shots and brews, ensuring that every single time you brew a well-balanced coffee, with a good level of complexity and sweetness.
Tamping Your Coffee
Tamping ground coffee is all part of the extraction process and requires you to do so with firm, even pressure to help form a solid, flat surface of coffee in the filter basket. Here is a quick guide to tamping before extraction your coffee.
- To tamp your coffee grounds, raise your elbow at a 90 degree angle and firmly pack the grounds with the hand tamp using 30 pounds of pressure.
- Use a downward twisting motion when coming up out of the tamp. The goal is to have an even level surface that will force the water to go through the grounds evenly.
- If too much water is put into the basket, it doesn’t leave enough room for expansion. A gap is needed for the water to spread evenly over the surface of the grounds.
- Wipe off any excess grounds that sit loosely on top or around the edges of the basket.
- Purge your espresso machine before inserting the portafilter into the group head to help the machine regulate the correct temperature for extraction.
- The extraction of shots should start out as a drip and last between 20-26 seconds. The end result should be a rust coloured crema on top that lasts a long time.
There are always two things to consider when tamping: level and pressure. Your puck needs to be as level as possible, because even if it is slightly uneven, it can cause the pressurised water to not make its way through the coffee evenly during extraction. To check it is level, raise the portafilter to eye height with the tamper still on top and twist the pipe to inspect it from different angles.
We have provided you with a list of all you need to get the coffee extraction process right from a fully functional espresso machine, to automatic grinder and fresh quality coffee beans.
- Espresso Machine
- Filtered Water
- Fresh Quality Coffee (try our 100 percent Fairtrade, Organically Certified Cafe Bonte coffee beans)
Extracting The Perfect Espresso Shot
You should now be ready to pour the perfect espresso extraction shot with your espresso machine. Remember, it is all about consistency. Make sure you do things exactly the same way every time. An espresso shot is a beverage made from ground coffee, poured from one side of a double portafilter in one continuous extraction. The coarser the ground coffee is, the faster the extraction will be. The finer the ground coffee, the slower it will be. A 20-30 second extraction shot is recommended for the ultimate espresso finish and crema layering.
- Place a pre-warmed cup beneath the portafilter and prepare a single or double espresso shot.
- The espresso will start to flow after 4-8 seconds and should produce a dark-brown crema.
- If the espresso starts to flow after less than 3 seconds then you have under dosed the filter basket and the grind is too coarse. This is an under-extracted shot.
- If the espresso starts to drip but doesn’t flow after 10 seconds, then you have over-dosed the filter basket and the grind is too fine. This is an over-extracted shot.
A great espresso shot is about achieving the perfect balance between sweetness, acidity and bitterness. The flavour of your coffee will depend on these many factors as highlighted in this article, including the type of coffee beans grind size, dose, coarseness or fineness of grind and tamping pressure. You can experiment by adjusting these factors to achieve your preferred taste.