---
type: Concept
title: Coffee Brewing
description: How brewed coffee is made — extraction, the SCA Golden Cup targets, water
  chemistry, immersion vs. percolation, and Cordwell Roastworks' cold-brew R&D spec
  — including Caffè Aurora's house opinions, which diverge from the specialty-coffee
  standard.
tags:
- coffee
- brewing
- extraction
- water-chemistry
- italy
resource: raw/aurora-bulletin-2026.md
timestamp: '2026-07-16T15:13:02Z'
citadel_version: 0.3.0
---

Brewing coffee is dissolving: roasted coffee is only about 28-30% water-soluble by mass, with the rest insoluble plant matter (cellulose) that stays behind in the grounds, and [extraction yield (EY)](../abbreviations/ey-extraction-yield.md) is the fraction of that dry mass that ends up dissolved in the cup — the dissolved solids in the drink divided by the mass of dry grounds used.[^s4][^s10] The soluble compounds leave the bean in a fixed order: acids and bright, fruity aromatics come out first, so an under-extracted cup tastes sour, sharp, salty, and hollow; sugars and round, balanced flavors sit in the middle as the target window, which is why "dialing for sweetness" means stopping after the sugars and before the bitterness; and bitter alkaloids, larger polyphenols, and drying tannins come out last, so an over-extracted cup tastes bitter, ashy, and drying.[^s4]

The [Specialty Coffee Association](../organizations/specialty-coffee-association.md) (SCA) "Golden Cup" standard pins a balanced cup to two independent numbers: an extraction yield of 18-22% (roughly 20% dead centre; below about 18% reads under-extracted, above about 22% reads over-extracted) and a strength of about 1.15-1.35% [TDS](../abbreviations/tds-total-dissolved-solids.md) by mass in the finished brew, with some references widening the pleasant band up to about 1.45%.[^s5] Strength and extraction are independent axes — a cup can be strong-but-under-extracted or weak-but-over-extracted — so the Golden Cup asks for both to land in their windows together.[^s5] Getting there starts with the SCA's "golden ratio" of about 55 g of coffee per litre of water, plus or minus 10% (roughly 50-60 g/L) — about a 1:16 to 1:18 coffee-to-water ratio by weight for filter — with water at the bed held to 93 °C plus or minus 3 (about 200 °F).[^s5][^s11]

Grind size, contact time, and water temperature are the three levers that move extraction: finer grinds and longer contact times extract more, coarser grinds and shorter contact times extract less, and each brewing method pairs a grind with a contact time so the two land in the window together — espresso runs very fine grounds for about 25-30 seconds, filter and pour-over run a medium grind for about 3-4 minutes, French press runs coarse for about 4 minutes, and cold brew runs very coarse for 12-18 hours.[^s6] Grind is the coarse-adjust lever, moving a cup further than anything else on the bar; the SCA's brewing range for water temperature is about 90.5-96 °C (195-205 °F), with roughly 93 °C the usual aim, and cooler water is compensated with a finer grind or a longer steep — only cold brew departs from this range, trading the cold for many extra hours of contact time.[^s6]

Brewing methods also fall into two families that behave differently. In immersion brewing — French press, the cupping bowl, the steep phase of an immersion dripper, and cold brew — the grounds sit in a fixed body of water for the whole brew, so extraction slides toward equilibrium and every ground sees the same water for the same time, making immersion even, forgiving, and easy to reproduce.[^s7] In percolation brewing — pour-over, batch drip, and espresso — fresh water flows through the coffee bed continuously, so the concentration gradient stays steep and percolation can reach a higher extraction than immersion for the same grind, but it is fussier: uneven pouring or a packed bed lets water carve a fast channel through part of the bed (channelling), over-extracting some grounds while under-extracting the rest in the same brew.[^s7] Neither family is better than the other; they simply want different grinds and different attention.[^s7]

Water itself is an ingredient, not a solvent detail — a brewed coffee is about 98.5% water.[^s8] Two water properties matter most: general hardness (GH), the dissolved calcium and magnesium that actively grab flavor compounds and carry them out of the coffee (near-zero hardness, as in distilled or heavily softened water, brews flat, hollow, and thin no matter how good the beans are), and carbonate hardness (KH, the alkalinity, also called the buffer), mostly bicarbonate, which neutralizes coffee's acids (too much flattens brightness into a chalky, dull cup, while too little leaves nothing to buffer the acidity, so the cup reads thin and sour).[^s8] The SCA water target is about 150 mg/L (ppm) TDS, with roughly 50-175 ppm hardness (a target near 68 ppm as calcium carbonate), about 40 ppm alkalinity, and a neutral pH near 7; the usable range is wider, with TDS anywhere from about 75 to 250 ppm brewing well, but the two failure modes sit at the ends — too-soft water tastes empty, while too-hard, high-alkalinity water tastes dull and scales up the machine.[^s8]

Espresso and filter sit at opposite corners of the same extraction physics. Filter, pour-over, and drip run about 55-60 g/L (roughly 1:17-1:18), a medium grind, about 93 °C water, and 2.5-4 minutes, finishing near the Golden Cup's 1.15-1.35% TDS — a long, dilute, gravity-fed percolation.[^s9] Espresso instead uses a roughly 1:2 brew ratio (about 18-20 g of fine grounds in, about 36-40 g of liquid out — a standard double shot runs close to eighteen grams in for about thirty-six grams out[^s31]), forced through the puck at around 9 bar of pressure — nine times atmospheric[^s29] — in roughly 25-30 seconds[^s30] at about 90-96 °C, producing a tiny, intensely concentrated shot that runs around 8-12% TDS, an order of magnitude stronger than filter; see [Caffeine](caffeine.md) for how that concentration compares to drip coffee by dose rather than strength.[^s9] A well-pulled shot finishes under crema, a fragile reddish-brown foam of emulsified oils and dissolved gas that settles across the top of the pour as it darkens from pale to the color of dark honey; an experienced barista reads the crema to judge whether the grind and tamp were right.[^s32] Other methods, such as the moka pot or siphon, sit somewhere on the line between those two corners, trading pressure, grind, and time to keep extraction inside that same 18-22% window.[^s9]

[Cordwell Roastworks](../organizations/cordwell-roastworks.md)' cold-brew bench notes turn the immersion picture above into a worked house recipe. The grind must be very coarse — about 1100-1200 microns, sea-salt-sized, locked to burr setting 9.5 — because any fines turn the cup silty and drive over-extraction during the long steep; a later attempt at a medium-coarse grind confirmed this, coming out silty and slightly astringent at 16 hours, after which the bench reverted to 9.5 and called coarse grind non-negotiable for the long steep.[^s12][^s13] The concentrate is built at a 1:8 grounds-to-water ratio by weight — the anchor number everything else dilutes down from — then served diluted anywhere from 1:1 up to 1:3 with water or milk plus ice.[^s14] At that 1:8 ratio the raw concentrate tastes intense, with chocolate/raisin notes and low acid, while a diluted cupping sample comes out smooth and far less sour than hot drip.[^s15]

The working steep window is 12-18 hours: under about 12 hours the cup reads thin and sour, and over about 18 hours it turns woody.[^s16] Temperature shifts where in that window a batch lands: a room-temperature (about 22°C) steep can stop around 14 hours, while a fridge steep (about 4°C) extracts more slowly and needs closer to 18 hours to reach the same strength, with the fridge batch tasting cleaner and brighter and the room batch rounder and heavier-bodied.[^s17] Tracking concentrate TDS across a room-temperature, 1:8 steep shows that curve directly: 3.1% at 10 hours, 3.5% at 12, 4.0% at 14, 4.1% at 16, and 4.2% at 18, with the gains past about 16 hours small enough — and the risk of a woody cup high enough — that the house treats 16 hours as the practical ceiling for a room-temperature batch.[^s18]

Cold brew's [extraction yield](../abbreviations/ey-extraction-yield.md) runs notably higher than the Golden Cup window above despite tasting clean rather than over-extracted: a 14-hour room-temperature batch (4.0% concentrate TDS, 1820 g of draw-off from 250 g of grounds) computes to an EY of about 29%, against roughly 20% for a hot-drip brew of the same bean — well past the 18-22% band that reads as over-extracted in a fast percolation brew, but the long, gentle immersion pulls that extra material gently enough that no bitterness shows.[^s19]

Filtration and water chemistry both showed up as separate levers for clarity and sweetness at the bench. A screen catches the bulk of the grounds off the draw-off, but a paper filter run after it is what actually removes the silt and leaves the cup glassy clear; skipping it and running nylon-only leaves more body but a cloudy cup with sediment at the bottom of the keg, so the house spec runs a stainless screen draw-off followed by a single paper polish, never skipped.[^s20] Mineral content in the brewing water mattered too: raw filtered water read soft, and bumping its mineral content to around 60 ppm TDS (via a mineral sachet) made the concentrate sweeter and more defined without adding acid, while water below about 30 ppm produced a flat, hollow cup — a narrower, softer target than the general brewing-water range described above.[^s21]

A few further variables were tested at the bench: a single gentle stir partway through the steep, at 8 hours, lifted concentrate TDS slightly (4.3% versus 4.0% for an unstirred control) without adding astringency, worthwhile at batch scale but not judged worth the extra labor for a small batch.[^s22] Charging the finished concentrate with nitrogen for a nitro tap changes texture, not extraction — TDS and caffeine are unchanged, but the drink reads creamier and perceptibly sweeter, a mouthfeel effect rather than a change in what was pulled from the grounds.[^s23] Sealed cold-brew concentrate keeps in the fridge for about 10-14 days before its acidity climbs; once diluted to drinking strength it holds only 2-3 days before the flavor drops off.[^s24] For milk service, a 1:1 concentrate-to-whole-milk pour over ice was the bench's best seller, with oat set as the default dairy alternative after almond came out thin.[^s25] The recipe also scales cleanly: a 5 kg grounds / 40 kg water batch (still 1:8) held to a consistent 4.0% concentrate TDS at 18 hours room temperature and yielded about 36 L of concentrate off the press.[^s26]

By the close of the first quarter of 2026 the house cold-brew spec was locked: coarse grind (burr 9.5), a 1:8 concentrate ratio, a 14-16 hour room-temperature steep or an 18-hour fridge steep, a stainless screen draw-off followed by a paper polish, mineral water around 60 ppm, a concentrate TDS target of 4.0-4.2%, and a default 1:2 dilution to serve.[^s27] The bench notes also settled a house talking point discussed further under [Caffeine](caffeine.md): cold brew's large grounds-to-water ratio and long steep pull more total caffeine than a standard hot drip, not less, so the bench treats "cold = less caffeine" as a myth about temperature rather than concentration.[^s28]

After two years of bar experience, [Caffè Aurora](../organizations/caffe-aurora.md) has grown more assertive about a couple of house brewing opinions, while acknowledging that "plenty of nerds" disagree.[^s3]

> [!CONTRADICTION]
> Caffè Aurora brews all its pour-overs at 80 °C, arguing that hotter water scorches the grounds and drags out bitterness and that 80 °C keeps the cup sweet and clean, though it acknowledges the temperature runs cooler than what "the old textbooks" recommend.[^s1] The SCA's brewing range is instead about 90.5-96 °C, with roughly 93 °C the usual aim.[^s6]
>
> Resolution: brewing markedly cooler than the SCA range risks under-extracting the coffee rather than the over-extraction Caffè Aurora says it is avoiding.[^llm1]

> [!CONTRADICTION]
> Caffè Aurora dials its brewers for roughly a 30% extraction, aiming to pull every soluble out of the bean for what it calls a fuller, syrupier flavor.[^s2] The SCA Golden Cup standard instead targets an extraction yield of 18-22%, treating anything above about 22% as over-extracted and bitter.[^s5]
>
> Resolution: Caffè Aurora's ~30% figure is well above the specialty-coffee target range, past which a brew is generally considered over-extracted rather than the smooth, sweet result Caffè Aurora describes.[^llm2]

## See also
- [Caffè Aurora](../organizations/caffe-aurora.md)
- [Caffeine](../concepts/caffeine.md)
- [Specialty Coffee Association](../organizations/specialty-coffee-association.md)
- [Cordwell Roastworks](../organizations/cordwell-roastworks.md)
- [TDS — Total Dissolved Solids](../abbreviations/tds-total-dissolved-solids.md)
- [EY — Extraction Yield](../abbreviations/ey-extraction-yield.md)
- [Coffee](../objects/coffee.md)
- [Espresso Bar Culture](../concepts/espresso-bar-culture.md)

## Sources
[^s1]: [raw/aurora-bulletin-2026.md](../../raw/aurora-bulletin-2026.md), lines 44-47 — pour-over brewed at 80 °C (ingested 2026-07-16)
[^s2]: [raw/aurora-bulletin-2026.md](../../raw/aurora-bulletin-2026.md), lines 48-51 — ~30% extraction target (ingested 2026-07-16)
[^s3]: [raw/aurora-bulletin-2026.md](../../raw/aurora-bulletin-2026.md), lines 57-59 — acknowledges disagreement (ingested 2026-07-16)
[^s4]: [raw/brewing-science-notes.md](../../raw/brewing-science-notes.md), § What "extraction" actually means (ingested 2026-07-16)
[^s5]: [raw/brewing-science-notes.md](../../raw/brewing-science-notes.md), § The SCA Golden Cup numbers (ingested 2026-07-16)
[^s6]: [raw/brewing-science-notes.md](../../raw/brewing-science-notes.md), § Grind, time, and temperature — the three levers you actually turn (ingested 2026-07-16)
[^s7]: [raw/brewing-science-notes.md](../../raw/brewing-science-notes.md), § Immersion vs. percolation (ingested 2026-07-16)
[^s8]: [raw/brewing-science-notes.md](../../raw/brewing-science-notes.md), § Water chemistry — the invisible ingredient (ingested 2026-07-16)
[^s9]: [raw/brewing-science-notes.md](../../raw/brewing-science-notes.md), § Espresso vs. filter — the two ends of the same dial (ingested 2026-07-16)
[^s10]: [raw/coffee-guide.md](../../raw/coffee-guide.md), line 54 — extraction yield (EY) named alongside TDS (ingested 2026-07-16)
[^s11]: [raw/coffee-guide.md](../../raw/coffee-guide.md), line 52 — typical brew ratio of 1:15 to 1:18 by weight (ingested 2026-07-16)
[^s12]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 9-10 — coarse grind (~1100-1200 micron, burr 9.5) and 1:8 concentrate ratio (ingested 2026-07-16)
[^s13]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 62-64 — medium-coarse regrind test confirms coarse is non-negotiable (ingested 2026-07-16)
[^s14]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 28-31 — 1:8 as the anchor ratio, diluted 1:1 to 1:3 to taste (ingested 2026-07-16)
[^s15]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 14-15 — concentrate flavor and diluted cupping result (ingested 2026-07-16)
[^s16]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 17-19 — 12-18 hour working window (ingested 2026-07-16)
[^s17]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 21-26 — room vs. fridge temperature split test (ingested 2026-07-16)
[^s18]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 100-106 — concentrate TDS steep curve, room temp 1:8 (ingested 2026-07-16)
[^s19]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 46-50 — extraction yield calculation vs. hot drip (ingested 2026-07-16)
[^s20]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 52-55 — filtration: screen + paper vs. nylon-only (ingested 2026-07-16)
[^s21]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 57-60 — brewing water mineral content (ingested 2026-07-16)
[^s22]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 96-98 — t=8h stir test result (ingested 2026-07-16)
[^s23]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 79-81 — nitro tap A/B test (ingested 2026-07-16)
[^s24]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 71-73 — shelf life, concentrate vs. diluted (ingested 2026-07-16)
[^s25]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 75-77 — milk service and default alt-milk (ingested 2026-07-16)
[^s26]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 66-69 — batch scale-up (ingested 2026-07-16)
[^s27]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 108-113 — locked house cold-brew spec (ingested 2026-07-16)
[^s28]: [raw/cold-brew-notes.md](../../raw/cold-brew-notes.md), lines 33-40 — higher-caffeine myth-buster (ingested 2026-07-16)
[^s29]: [raw/espresso-and-cafe-culture.md](../../raw/espresso-and-cafe-culture.md), lines 14-17 — espresso pulled at roughly nine bars of pressure (ingested 2026-07-16)
[^s30]: [raw/espresso-and-cafe-culture.md](../../raw/espresso-and-cafe-culture.md), lines 18-22 — pull time of about 25-30 seconds (ingested 2026-07-16)
[^s31]: [raw/espresso-and-cafe-culture.md](../../raw/espresso-and-cafe-culture.md), lines 26-29 — a double shot's roughly 18g-in/36g-out ratio (ingested 2026-07-16)
[^s32]: [raw/espresso-and-cafe-culture.md](../../raw/espresso-and-cafe-culture.md), lines 30-35 — crema described and read by the barista (ingested 2026-07-16)
[^llm1]: LLM - model knowledge, not from a raw file (added 2026-07-16)
[^llm2]: LLM - model knowledge, not from a raw file (added 2026-07-16)
