Brewing Coffee

What Is Brewing?

Brewing coffee is the process of combining roasted, ground coffee with water so that water-soluble compounds — acids, sugars, melanoidins, lipids, and aromatic molecules — dissolve into the liquid, creating the beverage we drink. The Specialty Coffee Association (SCA) and coffee science broadly define brewing as a controlled extraction: a deliberate effort to move a desired proportion of a coffee's dissolvable mass into the cup.

While preparation styles vary enormously — from a slowly hand-poured V60 to a fully automated espresso machine — all share four fundamental steps: the roasted beans are ground, the ground coffee contacts water for a defined time, the liquid is separated from the spent grounds, and the brewed coffee is served or stored. Every decision a brewer makes maps onto at least one extraction variable.

Characteristics that different preparation approaches emphasise or suppress include acidity (brightness), aroma (particularly delicate floral and citrus notes), mouthfeel (body), astringency, bitterness, and the duration of flavour perception in the mouth, commonly called the finish.

---

The Six Core Brewing Variables

Even with the same roast, the character of the extraction is highly dependent on a cluster of interacting variables. Understanding each individually is the first step to understanding how they compound.

1. Grind Size & Particle Distribution

Grind size is arguably the most powerful single variable available to a brewer. The fineness of the grind determines how much surface area is exposed to water, directly controlling the rate and completeness of extraction.

• Brewing methods with longer water-contact times require a coarser grind to avoid over-extraction.
• A grind that is too fine for the method will expose too much surface area, producing a bitter, harsh, over-extracted taste.
• A grind that is too coarse will produce weak, under-extracted coffee unless a higher coffee dose compensates.
• Grind uniformity is highly desirable: an uneven particle distribution means fine particles over-extract and coarse particles under-extract simultaneously, muddying the cup.

Burr mills — using two revolving abrasive elements of stainless steel or ceramic — are the preferred tool because they crush and shear beans with minimal frictional heat, releasing oils and producing a comparatively uniform particle distribution. Blade grinders, by contrast, chop beans unevenly, generating a wide spread of particle sizes that makes consistent extraction difficult.

Ground coffee deteriorates faster than whole roasted beans because of the greater surface area exposed to oxygen. Grinding immediately before brewing is the standard professional practice.

2. Water Quality & Composition

Water is roughly 98–99% of brewed coffee by mass, making its chemistry a critical but frequently overlooked variable. The mineral composition of brew water — particularly the levels of magnesium, calcium, and bicarbonate — affects both the efficiency of extraction and the perceived balance of the final cup. Hard water rich in bicarbonate can suppress acidity and produce flat-tasting coffee; very soft or distilled water can produce thin, sour results and may damage metal equipment over time.

3. Brew Temperature

Coffee is usually brewed hot, at a temperature close to the boiling point of water. Brew temperature influences the solubility of different compound classes: higher temperatures extract more rapidly and can favour the dissolution of bitter or astringent compounds, while lower temperatures slow extraction and may leave desirable acids and sweetness behind.

The commonly cited professional range for drip and pour-over brewing sits between approximately 90 °C and 96 °C (194 °F–205 °F), though the precise optimum depends on roast level, grind size, and brew method. Cold brew — in which grounds steep in cold or room-temperature water for many hours — is deliberately far below this range, producing a chemically distinct extraction profile characterised by lower perceived acidity.

4. Brew Ratio

The brew ratio — the mass of dry coffee grounds relative to the mass (or volume) of water used — sets the upper limit of potential strength in the cup. Preferred brew ratios of water to coffee commonly fall in the range of 15:1 to 18:1 by mass; even within this relatively narrow band, differences in strength and body are easily perceived by an experienced drinker. A ratio of 16:1, for example, means 62.5 g of coffee per 1,000 g of water.

Brew ratio and extraction yield interact: the same ratio can produce a very different cup depending on how completely the coffee's soluble mass is extracted.

5. Brew Time & Contact Time

The duration of contact between water and grounds governs how far extraction proceeds. In methods where contact time is fixed by the device (e.g. immersion brewers), adjusting grind size is the primary lever for correcting under- or over-extraction. In methods where time is adjustable (e.g. manual pour-over), a brewer may use a finer grind with a shorter brew time, or a coarser grind with a longer time, to reach a similar extraction yield while using less coffee.

6. Agitation & Turbulence

Agitation — stirring, swirling, blooming with a pre-infusion pour, or the turbulence of pressurised extraction — distributes water evenly through the coffee bed, reduces channelling, and accelerates the early stages of extraction. Uneven flow through a coffee bed is one of the most common sources of inconsistency across brew methods.

---

Extraction Yield and TDS: Measuring What's in the Cup

Two numbers sit at the centre of professional brewing evaluation. For a deeper treatment, see the dedicated article on Extraction: Yield & Strength.

Extraction yield (commonly expressed as a percentage) represents the proportion of the coffee's total dry mass that has dissolved into the brew water. Not all soluble material is desirable: under-extracted coffee (low yield) tends toward sourness and grassiness; over-extracted coffee (high yield) tends toward bitterness and astringency.

Total Dissolved Solids (TDS), typically measured with a refractometer and expressed as a percentage or in parts per million (ppm), describes the concentration of dissolved coffee compounds in the finished beverage — broadly equivalent to the brewer's concept of strength. A beverage can be low in TDS (weak) despite having a high extraction yield if a very high water-to-coffee ratio was used, illustrating why the two metrics are related but distinct.

Extraction yield can be calculated from TDS and brew ratio using a standard formula, allowing baristas and quality-control teams to audit consistency across batches without relying solely on taste.

---

The SCA Brewing Control Chart

The SCA Brewing Control Chart (derived from work originally developed in the mid-twentieth century and refined by the SCA) is the canonical graphical tool for visualising the relationship between extraction yield, TDS/strength, and brew ratio. It plots strength on one axis against extraction yield on the other, with brew ratio curves overlaid, defining a central "ideal" zone — sometimes called the target rectangle — that represents the range of combinations most tasters have historically found balanced and acceptable.

Key features of the chart:

• The target zone occupies a band of extraction yield and strength considered optimal by SCA standards; coffee that falls outside it is categorised as too strong, too weak, over-extracted, or under-extracted.
• Brew ratio curves run diagonally across the chart, illustrating how the same ratio can land in or outside the target zone depending on extraction completeness.
• The chart is a diagnostic tool, not a prescriptive recipe: different preparation methods, roast levels, and drinker preferences legitimately produce preferred cups outside the centre of the target zone.

The chart remains widely taught in SCA curricula and barista training programmes as a framework for systematic troubleshooting.

---

Brewing Methods Overview

All brewing methods are ultimately combinations of the six variables above, organised into a contact architecture. Major categories include:

• Percolation / Pour-Over: water passes continuously through a bed of grounds (e.g. drip machines, V60, Chemex). Grind size and pour technique control extraction rate.
• Immersion / Steeping: grounds are submerged in water for a set time, then separated (e.g. French press, AeroPress in immersion mode, cold brew). Contact time and ratio are the dominant variables.
• Pressure: water is forced through a tightly packed, finely ground puck at elevated pressure (espresso). The combination of fine grind, high pressure, and short contact time produces a concentrated beverage with a distinctive emulsified texture.
• Hybrid: methods combining elements of both percolation and immersion (e.g. AeroPress in percolation mode, Clever Dripper).
• Cold Brew: extended cold-water immersion over many hours, bypassing thermal extraction dynamics entirely.

Each method creates a different emphasis on the sensory characteristics noted above — acidity, body, aroma, finish — making method selection itself an expressive choice.

---

Freshness, Storage, and Practical Consistency

Extraction quality is bounded by ingredient quality. Roast freshness and grind freshness both constrain what any brewing technique can achieve:

• Ground coffee deteriorates faster than whole roasted beans due to the greatly increased surface area exposed to oxygen and moisture.
• Whole roasted coffee is frequently vacuum-packed or sealed with one-way valves to prevent oxidation.
• Grinding immediately before brewing is the standard recommendation for preserving volatile aroma compounds.

Process automation — from machines that grind, dose, and brew automatically to single-serve pod systems — trades some degree of variable control for repeatability and convenience. Professional and enthusiast practice favours manual or semi-manual control precisely because it allows each variable to be independently adjusted in response to changes in the coffee or environment.