pH and Acidity Adjustment: Principles and Protocols

Problem Definition

pH and titratable acidity (TA) independently affect wine quality: pH governs microbial stability, SO₂ efficacy, color stability, and oxidation resistance, while TA determines perceived acidity (sourness). The two parameters do not move in lockstep, creating situations where one value is acceptable and the other problematic.

Common scenarios requiring intervention:

• High pH (>3.6) with adequate TA: Microbial risk without sour taste
• Low pH (<3.0) with high TA: Excessive sourness despite stability
• Warm climate wines: High sugar with low acid and high pH
• Cool climate wines: Low sugar with high acid and low pH

Technical Context

pH vs. Titratable Acidity

Titratable acidity (TA):

• Total concentration of hydrogen ions (measured by titration to pH 8.2)
• Expressed in g/L as tartaric acid equivalent
• Typical range: 5-9 g/L
• Directly correlates with sour taste perception

pH:

• Logarithmic measure of free hydrogen ion activity
• Typical wine range: 3.0-4.0
• Governs chemical equilibria and microbial growth
• Small changes have large effects (0.1 pH change = 26% change in H⁺)

Buffering capacity:

• Wine’s ability to resist pH change upon acid/base addition
• Higher buffering = more acid needed to change pH
• Affected by tartrate, malate, and potassium concentrations

Effects of pH on Wine

Parameter	Low pH (<3.3)	Optimal (3.3-3.6)	High pH (>3.6)
SO₂ efficacy	High molecular SO₂	Balanced	Low molecular SO₂
Microbial stability	High	Moderate	Low (spoilage risk)
Oxidation resistance	High	Moderate	Low
Color stability (red)	Good	Moderate	Poor
MLF difficulty	High	Moderate	Easy
Taste perception	Sharp, angular	Balanced	Flat, flabby

Major Wine Acids

Tartaric acid:

• Primary grape acid; unique to grapes
• Most acid-stable during fermentation
• Subject to potassium bitartrate precipitation

Malic acid:

• Secondary grape acid; higher in cool climates
• Converted to lactic acid during MLF
• Creates “green apple” sharpness

Lactic acid:

• Product of MLF
• Softer perception than malic
• Contributes approximately half the TA of malic per mole

Citric acid:

• Minor grape acid
• Metabolized by LAB (produces VA and diacetyl)
• Used as additive in some jurisdictions

Options and Interventions

Acidification (Lowering pH / Raising TA)

Tartaric acid addition:

• Most common acidification method
• Addition rate: 1 g/L raises TA by ~1 g/L
• pH drop depends on buffering capacity; typically 0.1 pH per 1 g/L
• Best added pre-fermentation (integrates better; precipitation opportunity)
• Legal in most jurisdictions; some limits (e.g., EU: max 4 g/L for reds, 2.5 g/L whites)

Protocol:

1. Measure pH and TA
2. Conduct bench trial with incremental additions
3. Calculate addition rate based on target
4. Add acid; mix thoroughly
5. Remeasure after 24-48 hours (equilibration)

Timing considerations:

• Pre-fermentation: Best integration; tartrate precipitation during cold stabilization removes excess
• Post-fermentation: Quicker correction but less integration time
• At bottling: Emergency correction only; quality compromise

Citric acid:

• Stronger acid (lower pKa) than tartaric
• Less volume needed for same pH drop
• Risk: Metabolized by LAB to acetic acid and diacetyl
• Only use in wines that will not undergo MLF

Deacidification (Raising pH / Lowering TA)

Potassium bicarbonate (KHCO₃):

• Neutralizes tartaric acid
• Precipitates as potassium bitartrate
• Addition rate: 1.25 g/L KHCO₃ reduces TA by ~1 g/L
• Increases K⁺ → promotes further tartrate precipitation

Calcium carbonate (CaCO₃):

• Neutralizes tartaric and malic acid
• Precipitates as calcium tartrate
• Double salt precipitation at high doses removes both acids
• Calcium malate is slightly soluble; not fully removed
• Quality concerns at high doses (calcium haze risk)

Malolactic fermentation:

• Converts malic to lactic acid
• Reduces TA by 1-3 g/L (depending on malic content)
• Raises pH by 0.1-0.3 units
• Biological method; not instant

Cold stabilization:

• Chilling precipitates potassium bitartrate
• Reduces TA (tartaric removal) and may raise pH slightly
• Effect depends on initial tartrate/potassium balance

Electrodialysis:

• Removes potassium ions, inducing tartrate precipitation
• More controlled than chemical addition
• Equipment-intensive

pH Adjustment Without Major TA Change

Ion exchange resins:

• Exchange potassium for hydrogen ions
• Lowers pH without adding acid
• Some jurisdictions restrict usage

Blending:

• Blend high-pH wine with low-pH wine
• Requires available material with appropriate profile
• Most gentle intervention

Trade-offs and Risks

Over-acidification:

• Excessive tartness masks fruit
• May precipitate during cold stabilization (TA drops after addition)
• Difficult to reverse
• Conduct bench trials before cellar-scale addition

Under-acidification:

• Remaining high pH increases spoilage risk
• Reduced SO₂ efficacy requires higher free SO₂
• Color and oxidation stability compromised

Deacidification excess:

• pH may rise above safe range (>3.7)
• Calcium addition risks calcium tartrate haze
• Double salt precipitation removes too much acid

MLF after acidification:

• MLF will reduce TA further
• Plan acidification considering MLF TA reduction
• If blocking MLF, acidification target is final

Regulatory limits:

• EU limits tartaric acid additions
• Some appellations prohibit acidification entirely
• Deacidification not permitted in cool climate regions
• Check specific appellation regulations

Practical Implications

Variety-specific considerations:

• Sangiovese: Moderate natural acidity; Chianti Classico DOCG typically requires minimal adjustment. Hot vintages may need acidification. Complete MLF standard.

• Grenache: Low natural acidity and high pH typical. Châteauneuf-du-Pape wines often at pH 3.6-3.9. Acidification common to achieve microbial stability.

• Riesling: High natural acidity; Mosel wines may exceed 10 g/L TA. Residual sugar balances perception. Deacidification rarely needed; MLF typically blocked to preserve acidity.

• Chardonnay: Moderate acidity with significant regional variation. Warm-climate (Napa Valley) may need acidification; cool-climate may undergo full MLF for softening.

Appellation-specific implications:

• Chianti Classico DOCG: Acidification permitted; deacidification not (cool climate classification). Balance between Sangiovese’s natural acidity and vintage variation.

• Châteauneuf-du-Pape AOC: Hot climate produces high-pH wines. Acidification common for microbial stability. High-alcohol fermentation compounds pH management needs.

• Mosel: Deacidification historically permitted given high natural acidity. Modern practice often uses residual sugar for balance rather than deacidification.

• Napa Valley AVA: No appellation-level restrictions on acid adjustment. Acidification is standard practice for Cabernet Sauvignon in warm vintages.

References

• Ribéreau-Gayon, P., Glories, Y., Maujean, A., & Dubourdieu, D. (2006). Handbook of Enology, Volume 2: The Chemistry of Wine Stabilization and Treatments (2nd ed.). Wiley. Publisher Link

• Ough, C.S., & Amerine, M.A. (1988). Methods for Analysis of Musts and Wines (2nd ed.). Wiley-Interscience. Publisher Link

• Waterhouse, A.L., Sacks, G.L., & Jeffery, D.W. (2016). Understanding Wine Chemistry. Wiley. DOI: 10.1002/9781118730720

• OIV. (2021). International Code of Oenological Practices. Organisation Internationale de la Vigne et du Vin. https://www.oiv.int/