tags: [] - coffee/brewing - coffee/brewing/water aliases: - Water alkalinity - Total alkalinity coffee - Bicarbonate alkalinity

Alkalinity¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: Water alkalinity, Total alkalinity coffee, Bicarbonate alkalinity Related: Water in Coffee MOC | KH (Carbonate Hardness) | pH | Bicarbonate in Coffee Water | High Alkalinity Problems Status: ✅ Complete

Overview¶

Alkalinity in the context of coffee water refers to the water's capacity to neutralise acids — its buffering capacity against acidification. In natural and municipal water, alkalinity is primarily contributed by bicarbonate ions (HCO₃⁻), with minor contributions from carbonate (CO₃²⁻) and hydroxide (OH⁻). Alkalinity is the most flavour-critical water chemistry parameter for coffee: bicarbonate ions in brewing water chemically neutralise the organic acids (citric, malic, acetic, quinic) extracted from coffee grounds during brewing, raising the pH of the extract and directly suppressing the perceived acidity and brightness of the resulting cup. High-alkalinity water is the single most common cause of flat, dull, and bitter-tasting coffee in commercial and domestic settings worldwide.

The Chemistry of Alkalinity and Coffee¶

When organic acids extracted from coffee contact bicarbonate-containing water, a neutralisation reaction occurs:

HCO₃⁻ + H⁺ → H₂O + CO₂

This reaction consumes both the bicarbonate ion and a hydrogen ion (H⁺) from the organic acid, raising the solution pH and reducing free acid concentration. In practical terms:

Citric acid + bicarbonate → water + CO₂ + reduced perceived citrus brightness
Malic acid + bicarbonate → water + CO₂ + reduced apple/stone-fruit character
Total acidity is reduced; perceived balance shifts toward bitterness and flatness

At high bicarbonate levels, virtually all extractable organic acid is neutralised before it can contribute to the cup's flavour profile. The result is a cup that tastes bitter, flat, and lacking in any of the origin-specific fruit or floral characteristics that define specialty coffee quality.

Alkalinity vs. pH¶

Alkalinity and pH are related but distinct:

pH measures the current concentration of hydrogen ions (H⁺) in the water — a snapshot of acidity or alkalinity at a moment in time
Alkalinity measures the buffering capacity — how much acid the water can absorb before its pH changes significantly

A water sample can have pH 7.5 (slightly alkaline) with low buffering capacity (low bicarbonate), or pH 7.5 with high buffering capacity (high bicarbonate). For coffee, alkalinity matters more than pH: a slightly alkaline pH with low bicarbonate is relatively harmless; a moderately alkaline pH with high bicarbonate has significant flavour impact.

Alkalinity Units and Measurement¶

Alkalinity is expressed in: - mg/L as CaCO₃ (the SCA standard unit) - mg/L as HCO₃⁻ (direct bicarbonate concentration) - °KH (German degrees of carbonate hardness) = 1°KH = 17.85 mg/L as CaCO₃

Conversion: mg/L as CaCO₃ × 1.22 = mg/L as HCO₃⁻

Measurement methods include: - Titration kits: Acid titration with bromocresol green or methyl orange indicator; drops to colour change indicate alkalinity - Electronic pH meters with calculation: Less accurate for alkalinity - Laboratory ICP or ion chromatography: Most accurate

SCA Alkalinity Target¶

SCA target: 40 mg/L as CaCO₃ (approximately 49 mg/L HCO₃⁻, or approximately 2.2°KH)

At this level, the water has sufficient buffering to prevent the brew from becoming excessively acidic, while not suppressing coffee's natural acid character.

Alkalinity thresholds: - Below ~20 mg/L as CaCO₃: Very low buffer; coffee can taste sharp or sour; suitable for acidity-emphasising applications with light roasts - 40–70 mg/L as CaCO₃: SCA acceptable range; mild buffering without significant flavour impact - 70–120 mg/L as CaCO₃: Increasing alkalinity; acidity suppression noticeable in lighter roasts; dark roasts may benefit (perceived bitterness slightly softened) - Above 150–200 mg/L as CaCO₃: Significant flatness; coffee tastes one-dimensionally bitter; most urban municipal water supplies in hard-water regions fall in this range

Relationship to KH (Carbonate Hardness)¶

Total alkalinity and carbonate hardness (KH) are numerically identical in most natural water where bicarbonate is the dominant anion — the two terms are often used interchangeably. KH (Karbonathärte) is the German water quality term for the same concept. See KH (Carbonate Hardness).

Managing High Alkalinity¶

Options for reducing alkalinity in brewing water: - Reverse osmosis (RO): Removes essentially all ions, including bicarbonate; requires remineralisation afterward - Ion exchange (deionisation): Specific anion exchange resins can selectively remove bicarbonate - Blending with RO or distilled water: Dilutes alkalinity without full treatment - Acid addition: Adding small amounts of food-grade acid (citric, lactic, phosphoric) to directly neutralise bicarbonate; used in some café operations but can be tricky to control precisely

Key Facts¶

Alkalinity is water's acid-buffering capacity, primarily from bicarbonate ions (HCO₃⁻); it is the most flavour-critical water parameter for coffee
Bicarbonate neutralises organic acids extracted from coffee during brewing, suppressing perceived acidity and brightness
SCA target: 40 mg/L as CaCO₃; high alkalinity (above ~100 mg/L) causes flat, dull, bitter cups regardless of coffee quality
Alkalinity and pH are related but distinct: alkalinity measures buffering capacity; pH measures current hydrogen ion concentration
High alkalinity is managed by RO, blending with soft water, or acid addition; it cannot be removed by simple carbon filtration or boiling

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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