As a barista you are making assessments about your extractions by how the coffee tastes every day. You can quantify extraction by measuring TDS (total dissolved solids) using a refractometer, but most cafes don’t have ready access to one. Using your sense of taste and your brew recipe (as explored in our last post) you can hit that ideal extraction.
So, let’s break down the common tastes and causes associated with four levels of extraction. From here we can effectively troubleshoot our extractions.
Over extraction is when we extract more than the desired solubles from the coffee. There are several things that can cause over extraction including an overly fine grind, long total brew time, temperature too high, a high brew ratio (dose : beverage weight) that results in excessive beverage weight verses dose that doesn’t match the brew recipe.
Over extraction may taste bitter and dry with a hollow mouthfeel and an unpleasant finish. One or more of these taste characteristics may be present in over extracted coffee.
Under extraction is when we extract less than the desired amount of solubles. It can be a result of a short total brew time, low temperature, a grind that is too coarse, or a low brew ratio (dose : beverage weight) that results in insufficient beverage weight verses dose that doesn’t match the brew recipe.
Under extraction will taste sour, lack sweetness, have aggressive acidity and exhibit a salty and short finish. One or more of these taste characteristics may be present in under extracted coffee.
Before we make changes to the grind based on tastes of over or under extraction we need to rule out uneven extraction.
Uneven extraction will present tastes associated with both under and over extraction at the same time.
It is typically caused by poor or inconsistent technique, resulting in channeling. Factors like an uneven distribution, un-level tamp, stepped basket shapes (as with a single basket), fractured coffee bed (from tapping the portafilter with the tamp), under dosing or too fine a grind leading to a floating puck can all contribute to channeling. It can occur sporadically or with nearly every shot.
An ideal extraction is what we strive for. It is the best any given coffee can taste. It can only be achieved with a bed of coffee that is extracted evenly, at the correct temperature, with the correct brew ratio (dose : beverage weight) and contact time (total brew time). When this happens, you will extract the desired amount of solubles from the coffee.
Ideal extraction will taste sweet, balanced, vibrant and complex.
FIXING EXTRACTION PROBLEMS
So how do we fix these extraction problems? Where do we start?
Rule out channeling from poor and inconsistent technique. Maintain the consistency and accuracy of your technique. Check for issues that cause channeling and variations in dose, distribution and tamping.
2) BREW RECIPE
Refer to your brew recipe. Stepping outside of the brew recipe parameters can lead to extraction problems. These recipes have been created and tested to give you an ideal extraction and the best tasting coffee possible. Variations to this recipe only work when you understand the effect of each variable on each other and to the extraction as a whole. Understanding brew ratios is key to this. We will explore brew ratios in another post. Keep in mind some non-standard equipment set ups may need variations to the brew recipe to get the best result.
After you rule out technique and brew recipe as causes for your extraction problem the next thing to look at is equipment faults.
A dirty grinder can cause flavor taints and inconsistent dosing. Clean your hopper and dosing chambers daily and don’t leave coffee in the grinder overnight.
Old water filter or problems with your water supply (like council works) can bring about flavor taints in your brews. If taste problems appear after water supply works then this could be a contributor.
Grinder blades wear and change the way they grind the beans. The particle size spread widens resulting in higher proportions of fines and boulders. Often you will tighten the grind to compensate and this can cause symptoms of uneven extraction.
This is where daily cleaning and preventative equipment maintenance is key. Prevent the problem before it occurs.
EXTRACTION ANALYSIS IN THE ROASTERY
Every day here in the Roastery we measure extraction by analysing the Total Dissolved Solids (TDS), using a refractometer. We check the resulting espresso and filter extractions from roast to roast, giving us tangible numbers that inform us about our extraction and the performance of our logged roast curves. This quality control allows us to refine our roasts and catch any problems before they reach you. It is a small part of the toolkit we use daily deliver consistent coffees to you. Measuring TDS is the next step on from using your taste and brew recipes to fine tune extractions. We will expand on the theory and use of this advanced tool in coming posts.
An ideal extraction makes a tasty coffee and you are already using your sense of taste each day to find it. What we have just covered gives you the information you need to interpret what you are tasting in the cup. Keep tasting, analysing and hit that ideal extraction.