tags: [] - coffee/brewing - coffee/brewing/water aliases: - Alkalinity and coffee acidity - Bicarbonate and acidity - How alkalinity affects acidity

Alkalinity and Acidity¶

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

Overview¶

Alkalinity and acidity in coffee are directly opposed through a chemical neutralisation reaction: bicarbonate ions (HCO₃⁻) in brewing water react with hydrogen ions (H⁺) from extracted organic acids, consuming both and producing water and carbon dioxide. The practical result is a direct suppression of perceived acidity in the cup — higher water alkalinity yields less bright, less fruity, and less complex coffee, because the organic acids responsible for these flavour attributes are chemically removed from the extract during brewing.

The Neutralisation Reaction¶

When coffee grounds contact hot bicarbonate-containing water, organic acids are extracted and immediately begin reacting with bicarbonate:

HCO₃⁻ + H⁺ → H₂O + CO₂↑

This reaction is fast, exothermic, and essentially complete at brewing temperatures. The CO₂ produced is released as gas; the remaining solution has fewer free hydrogen ions (higher pH) and lower free acid concentration. In sensory terms, brightness, citrus, stone fruit, and berry character — all primarily attributable to organic acids — are reduced.

Specific Acids Affected¶

Organic acid	Flavour contribution	Effect of alkalinity
Citric acid	Citrus brightness, lemon, lime	Neutralised to sodium/calcium citrate — flat
Malic acid	Apple, stone fruit, green apple	Neutralised to malate salts — reduced brightness
Acetic acid	Vinegary brightness, complexity	Partially neutralised
Quinic acid	Dry, astringent bitterness	Relatively less affected (pKa considerations)
Phosphoric acid	Clean, precise acidity	Neutralised
Lactic acid	Smooth, rounded acidity	Neutralised

Quinic acid, produced during roasting from chlorogenic acid degradation, contributes dry, bitter character and is somewhat less neutralised by bicarbonate because of its lower ionisation constant. High-alkalinity water thus preferentially preserves bitter quinic compounds while suppressing the brighter, more pleasant organic acids — exacerbating the perception of bitterness and flatness.

Threshold Effects¶

At low alkalinity levels, partial buffering can actually smooth harsh acidity in very light or sour-tending coffees. At the SCA target of 40 mg/L as CaCO₃, mild buffering occurs without significant acid suppression. Above approximately 70–100 mg/L, acidity suppression becomes perceptible. Above 150 mg/L, the cup is noticeably flat; above 200 mg/L, most perceived acidity is eliminated.

Alkalinity (mg/L as CaCO₃)	Acidity effect
< 20	Minimal buffering; full acid expression; can taste sharp
20–70	SCA range; mild buffer; acid preserved with slight rounding
70–120	Moderate acid suppression; lighter roast brightness reduced
120–200	Significant suppression; flat cups; darker roasts less affected
> 200	Near-complete neutralisation; one-dimensional bitterness

Key Facts¶

Alkalinity and acidity are chemically opposed: bicarbonate neutralises organic acids extracted from coffee
The reaction HCO₃⁻ + H⁺ → H₂O + CO₂ consumes both bicarbonate and organic acid ions, raising cup pH and reducing perceived brightness
Citric, malic, and phosphoric acids — responsible for fruity brightness — are preferentially neutralised; bitter quinic acid is relatively preserved, worsening flavour imbalance
SCA alkalinity target (40 mg/L as CaCO₃) balances mild buffering against acid preservation

References¶

Changelog¶

Date	Change
2026-04-28	Note created

This article is part of All-About-Coffee.com - The comprehensive coffee knowledgebase.