Extraction science
36 expert answers on extraction science. Click any question for the full answer. 36 questions.
How do you adjust grind to correct extraction?
If the coffee is under-extracted (sour, salty, hollow), tighten the grind by one step. If it is over-extracted (bitter, astringent, ashy), open it by one step. One step typically moves EY by 1-2 points. Change one variable at a time, keeping dose, ratio, temperature and water constant to isolate the
What is agitation in filter coffee and what role does it play?
Agitation in filter coffee refers to any technique that creates movement in the coffee bed or liquid during brewing, spinning the V60 (Rao spin), spoon stirring, turbulent pouring. It improves extraction uniformity by bringing all coffee particles into contact with water more evenly, and can signif
How to avoid channeling in espresso?
Channeling occurs when water takes a preferential path through the coffee puck, over-extracting some zones while leaving others under-extracted. To avoid it: distribute coffee evenly in the portafilter (ideally using WDT technique), tamp horizontally and with consistent force, and use a quality port
What is the bloom in pourover?
The bloom is the initial wetting phase of a pourover: you pour 2 to 3 times the dry coffee weight of hot water and wait 30 to 45 seconds for trapped CO₂ to escape. Skip the bloom and the violent degassing carves channels through the bed, producing a patchy, more acidic and under-extracted cup.
Why isn't bottled water always ideal for coffee?
Because most bottled waters are formulated for cold drinking, not for coffee extraction. Many are over-mineralised (Contrex, Hépar, Vittel) or too alkaline (San Pellegrino), and some lack magnesium. Only a handful (Volvic, Spa Reine, Mont Roucous) drift close to the SCA window, and most of those st
What is the brew chart or Golden Cup standard?
The Brewing Control Chart, the SCA's 'Golden Cup', is a two-axis diagram: EY on the x-axis (14 to 26 %) and TDS on the y-axis (0.8 to 1.8 %). At its centre, a rectangular sweet spot (EY 18-22 % / TDS 1.15-1.35 %) defines a balanced filter coffee per the SCA standard.
What is bypass in filter brewing?
Bypass in filter coffee is a technique that involves brewing coffee more concentrated than the target, then diluting it by adding cold or room-temperature water directly into the extracted liquid. It separates control of extraction (yield) from control of final concentration (TDS), offering more fle
Why does calcium matter in coffee water?
Calcium (Ca²⁺) mainly contributes body and texture to the cup. It promotes the extraction of compounds that add roundness and richness, but at excessive concentrations it causes limescale in machines and can make the profile heavy. The SCA recommends calcium hardness between 17 and 68 mg/L (as CaCO₃
How to calculate extraction yield at home?
Extraction yield is calculated with the formula: Yield (%) = (TDS% × beverage weight in g) / dry coffee weight in g × 100. For example, a V60 with 15 g coffee, 240 g liquid in the cup and TDS 1.35%: Yield = (0.0135 × 240) / 15 × 100 = 21.6%. The SCA ideal zone for filter is 18-22%.
What is channeling in espresso?
Channeling is an extraction flaw where pressurised water finds a preferential path through the coffee puck and bypasses the rest of the bed. The result is a globally under-extracted shot with locally over-extracted spots, yielding the clashing combination of sharp acidity and dry bitterness in the s
Charcoal-filtered vs reverse osmosis water for coffee: what's the difference?
An activated carbon filter removes chlorine, chloramines, certain pesticides and organic off-flavours, but retains most dissolved minerals (calcium, magnesium, bicarbonates). Reverse osmosis removes virtually all dissolved substances, minerals included, producing near-pure water. For coffee, rever
Why does the coffee-to-water ratio matter?
The brew ratio sets the final concentration of the cup at any given extraction. Reference windows: 1:2 for espresso (18 g → 36 g), 1:15 to 1:17 for filter, 1:14 to 1:16 for French press, 1:8 to 1:12 for concentrated cold brew. Changing the ratio alone moves TDS but not EY.
What is an espresso puck and what is it used for?
The espresso puck refers to the disc of ground coffee tamped in the portafilter, both before and after extraction. The term applies to the prepared coffee bed (the 'raw' puck) and to the wet coffee cake remaining after the shot. The state of the puck after extraction, called 'puck autopsy', is one
What is even extraction in coffee and why does it matter?
Even extraction means water flows uniformly through the entire coffee bed, extracting each particle at the same rate. When extraction is uneven, some zones over-extracted, others under-extracted, the cup simultaneously combines bitter and sour flavours, making diagnosis difficult and the profile u
How to measure the TDS of your coffee cup?
To measure coffee TDS, use a coffee refractometer. Take a few millilitres of coffee cooled to room temperature (~20°C), place 1-2 drops on the prism, and read the result in °Brix. Convert to % TDS using a standard correction factor (typically ×0.85 for filter, depending on the instrument). The measu
What is the ideal alkalinity for coffee water?
The ideal alkalinity for coffee water is around 40 mg/L (expressed as CaCO₃) according to SCA guidelines, which corresponds to roughly 2.2 degrees KH. Below 30 mg/L, the cup lacks buffering capacity and acidity becomes aggressive; above 80 mg/L, bicarbonates neutralise too many of the coffee's organ
What is the ideal brewing temperature for coffee?
The ideal extraction window sits at 90-96 °C, with 92-94 °C as the default for a medium roast, 94-96 °C for a light Scandinavian roast, and 88-92 °C for a dark roast or robusta. Above 96 °C, water loses most of its dissolved oxygen and drifts into over-extraction.
What is the ideal espresso pressure?
The standard espresso pressure is 9 bar, established as the reference by Italian tradition and adopted by most semi-automatic machines. It is not a universal truth, however: pressures between 6 and 12 bar are used depending on style and equipment, and pressure profiling (varying pressure during extr
What is an ideal extraction yield?
The ideal extraction yield (EY) sits between 18 and 22 %, as set by the SCA Golden Cup standard: it is the percentage of the dry grind that actually ends up dissolved in the cup. Below it the coffee tastes sour; above it, bitter and astringent. The 20-21 % band is the preferred sweet spot of special
What is the ideal TDS for an espresso?
The ideal TDS (Total Dissolved Solids) for espresso falls between 8% and 12% by mass concentration, with a common specialty target around 9-10%. Below 8%, the espresso is often watery and underdeveloped; above 12%, it becomes overly concentrated, bitter and thick. These values are measured with a co
What is the ideal TDS for filter coffee?
The ideal TDS for filter coffee (V60, Chemex, batch brew, AeroPress, etc.) falls between 1.15% and 1.45% by mass, according to the SCA Brewing Control Chart (BCC). The central value of 1.30% is often cited as the reference target. Below 1.15% the cup is too weak; above 1.45% it is too strong and may
What is the ideal water hardness for coffee?
The SCA standard calls for a total hardness (GH) of 50-175 mg/L CaCO₃, roughly 5-17 °f, with alkalinity (KH) at 40-75 mg/L CaCO₃. The median target usually quoted is about 150 mg/L TDS, GH 68 mg/L, KH 40 mg/L, enough to extract, not enough to scale.
Why is magnesium key in coffee water?
Magnesium (Mg²⁺) is the most important mineral ion for coffee aromatic extraction. It specifically promotes the solubilisation of fruity and floral compounds, and has a higher affinity than calcium for the organic acids and aromatic molecules in coffee. The SCA recommends a minimum of 10 mg/L; optim
What is Matt Perger's extraction theory?
Matt Perger, Australian barista and founder of Barista Hustle, helped popularise the idea that coffee's resistance to water flow (not time alone) is the key variable in espresso. His 'coarse fast / fine slow' theory highlights that two espressos with identical times but different grind sizes have ve
What is over-extracted coffee?
Over-extracted coffee is coffee whose extraction yield (EY) climbs above 22 %: the water has pulled heavy phenolic compounds and partly soluble tannins on top of the good solubles. In the cup: dry bitterness, tannic astringency, ashy finish, sometimes a medicinal edge.
What is particle size distribution (PSD) in coffee?
PSD (Particle Size Distribution) describes the range of particle sizes produced by a coffee grinder. A grinder creates particles of varying sizes, from very fine (< 100 µm, called 'fines') to coarse (> 1000 µm, 'boulders'). The width and shape of this distribution directly influences extraction qua
What is pre-infusion and why use it?
Pre-infusion is a gentle wetting phase applied to ground coffee before full-pressure extraction. It lasts 2-10 seconds in espresso (1-3 bar) and 30-45 seconds in filter brewing (the bloom). Its job: degas CO₂, saturate the bed evenly, and prevent channeling and uneven extraction.
What is the SCA extraction formula?
The SCA extraction formula is: Yield (%) = (TDS × beverage weight) / coffee weight × 100. It positions any coffee on the Brewing Control Chart (BCC), a two-dimensional graph linking TDS and yield to define the optimal quality zone (TDS 1.15-1.45%, yield 18-22% for filter). This theoretical framework
What is the Third Wave Water recipe?
Third Wave Water (TWW) is an American brand that sells mineral concentrate sachets to dissolve in demineralised or reverse-osmosis water, creating an ideal mineral profile for coffee. The recipe targets roughly 150 mg/L total TDS with a precise balance of magnesium, calcium and bicarbonates, within
What is under-extracted coffee?
Under-extracted coffee is coffee whose extraction yield (EY) falls below 18 %: only the first soluble families (acids, partial caffeine) have been dissolved. In the cup you get aggressive acidity, a salty finish, a hollow grassy taste and an absence of sweetness.
Why does water quality matter for coffee?
Because 98-99 % of a cup of coffee is water. Dissolved minerals, magnesium, calcium, bicarbonate, drive the extraction of aroma molecules, while chlorine or excess carbonate kill acidity and mute flavour. The target zone: roughly 75-150 mg/L of mineral TDS in the brew water.
What is coffee extraction?
Coffee extraction is the transfer of soluble compounds from ground coffee into water. Roughly 28-30 % of the bean is soluble, yet only 18-22 % should end up in the cup for a balanced brew. Below that window coffee tastes sour and grassy; above it, bitter and astringent.
What is differential solubility in coffee compounds?
Coffee extraction is a time-selective dissolution. Hot water attacks the coffee in successive layers, according to the solubility of each family of molecules.
What is EK43-style espresso?
Traditional espresso uses a conical or disc grinder set very fine (50-200 µm) to create the hydraulic resistance needed for pressure extraction. The EK43, with its 98 mm flat burrs, produces an exceptionally narrow particle size distribution (PSD) with very few fines, even at espresso-fine settings.
What is James Hoffmann's ultimate V60 recipe?
The recipe uses a 60 g/L ratio (30 g coffee to 500 mL water) and water at 93 °C. The process unfolds in five distinct steps.
What is TDS in coffee?
TDS (Total Dissolved Solids) is the mass percentage of dissolved matter in the beverage: 1.15-1.45 % for espresso, 1.25-1.55 % for filter coffee. A digital refractometer (VST LAB Coffee III, Atago PAL-COFFEE) reads it in seconds. It is the objective gauge of perceived strength in the cup.