Acidity Types in Wine

Acidity in wine is composed of several organic acids that develop through grape ripening, alcoholic fermentation, and post-fermentation biochemistry. Tartaric and malic acids originate in the grape berry itself and carry through into the finished wine. Lactic acid forms primarily during malolactic fermentation. Succinic acid is produced de novo by yeast during alcoholic fermentation. Acetic acid emerges as a byproduct of microbial metabolism or oxygen exposure. Citric acid is present only in trace amounts. These acids are measured collectively as titratable acidity, which for most table wines falls in a desirable range of approximately 5.5 to 8.5 g/L.

• Tartaric acid: the principal fixed acid in grapes, stable during ripening and resistant to microbial degradation
• Malic acid: the second most abundant grape acid, decreasing progressively during ripening, especially in warm climates
• Lactic acid: not present in fresh grapes in appreciable quantities; produced by lactic acid bacteria during MLF
• Succinic, acetic, and citric acids: minor contributors with specific sensory and stability roles, arising from yeast and bacterial metabolism or in trace form from grapes

Each acid type produces distinct sensory impressions. Tartaric acid delivers clean, bright, linear acidity associated with freshness and mineral character. Malic acid presents as sharp and green-apple-like, sometimes herbaceous, because the word malic derives from malum, Latin for apple. Lactic acid, being monoprotic and milder than malic, contributes a softer, creamier mouthfeel after MLF. Citric acid adds a lemony brightness but is used sparingly due to its intense sour flavor. Succinic acid imparts a complex combination of sour, salty, and bitter notes. Acetic acid at elevated levels produces a pungent, vinegary aroma. Research confirms that perceived sourness in order from more to less intense runs: malic, tartaric, citric, and then lactic.

• Tartaric: bright, clean, mineral-driven acidity; prominent in cool-climate Riesling and Champagne base wines
• Malic: sharp, green-apple character; noticeable in wines that have not undergone MLF, such as most German Riesling
• Lactic: softer, rounder, slightly creamy; characteristic of barrel-fermented Chardonnay that has completed MLF
• Acetic: vinegary, pungent; a recognized wine fault when volatile acidity rises above sensory threshold of approximately 0.7 g/L

Climate is arguably the most important environmental factor shaping acid composition in grapes. Tartaric acid levels remain relatively stable during ripening regardless of temperature, while malic acid is actively consumed through respiration, with degradation accelerating at higher temperatures. Cool-climate regions such as Burgundy, Mosel, and Champagne retain higher malic acid concentrations because slower ripening limits its degradation. Warm regions experience more complete malic acid breakdown by harvest, leaving wines tartaric-acid dominant and often benefiting from MLF to soften acidity. Grapes from warm climates can also be low in total acidity, prompting winemakers to add tartaric acid before fermentation to restore balance.

• Cool climates retain higher malic acid, producing wines with more pronounced, gripping acidity that benefit from MLF or contribute to freshness when MLF is blocked
• Warm climates see significant malic acid degradation, leaving tartaric acid as the dominant acid and creating rounder, lower-acid profiles
• High-altitude vineyards experience cooler nights that slow malic acid respiration, helping preserve acidity even in warm regions
• Vintage variation directly impacts malic acid levels; cooler growing seasons retain more malic acid than warmer ones in the same appellation

Malolactic fermentation is the conversion of sharper diprotic malic acid into softer monoprotic lactic acid by lactic acid bacteria, most commonly Oenococcus oeni. Because malic acid has two acidic protons and lactic acid has only one, the contribution of lactic acid to titratable acidity is roughly half that of malic acid, which is why MLF reduces TA by 1 to 3 g/L and raises pH by approximately 0.3 units. MLF is standard practice in virtually all red wine production globally and is common in premium white wines such as oaked Chardonnay. It is generally avoided in aromatic white varieties such as Riesling and Sauvignon Blanc, where malic crispness is considered a positive quality trait. Diacetyl, a byproduct of LAB metabolism during MLF, is responsible for buttery or creamy aromas and is more perceptible in white wines due to lower sensory thresholds.

• Full MLF: standard in most red wines worldwide; softens acidity, adds textural richness, and improves microbial stability by removing malic acid as a nutrient source for spoilage organisms
• MLF in whites: used for Chardonnay in Burgundy, California, and other premium regions to add texture; diacetyl contributes a buttery note, which is more prominent in whites
• Blocked MLF: deliberately prevented in aromatic whites such as Riesling and Sauvignon Blanc to preserve crisp malic acidity and primary fruit character
• O. oeni preferred: winemakers favor this species because it tolerates low pH and standard alcohol levels and produces minimal biogenic amines compared to other lactic acid bacteria

The acid composition of wine directly governs its microbial stability, color, and longevity. pH, which is inversely related to acidity, is the critical parameter for microbial control: lower pH values inhibit spoilage organisms and slow oxidation reactions. Tartaric acid is biologically stable and resistant to microbial degradation, making it the preferred acid for winemakers acidifying low-acid musts. During and after fermentation, potassium bitartrate crystals can precipitate, which is why winemakers use cold stabilization or electrodialysis to prevent visible tartrate deposits in finished wines. The OIV sets the maximum volatile acidity limit at 1.2 g/L acetic acid for still wines, while quality producers typically target below 0.6 g/L. Succinic acid, while generally stable, has been shown to inhibit MLF at concentrations above 1 g/L by interfering with Oenococcus oeni activity.

• Tartaric acid stability: resistant to microbial attack under normal winemaking conditions, unlike malic or citric acid; this is why it is the preferred acid addition for acidification
• Cold stabilization: exposes wine to sub-zero temperatures to encourage precipitation of excess potassium bitartrate crystals before bottling
• pH thresholds: wines below pH 3.5 present more favorable conditions for MLF bacteria, though higher pH also encourages spoilage organisms, making SO2 management critical
• Acetic acid bacteria: oxygen-dependent organisms such as Acetobacter that convert ethanol to acetic acid; controlled by minimizing oxygen exposure and maintaining adequate SO2 levels

Modern winemakers rely on titratable acidity (TA) and volatile acidity (VA) measurements to monitor acid profiles and guide cellar interventions. TA captures the total concentration of fixed acids and is typically expressed in grams per liter as tartaric acid equivalents. VA measures acetic and other steam-distillable acids. To track MLF progress specifically, winemakers test for residual malic acid using enzymatic kits or HPLC; MLF is considered complete when malic acid falls below approximately 0.1 g/L. Both TA and pH must be assessed together, as they interact in ways neither measurement alone can capture. Monitoring these parameters allows winemakers to make informed decisions about acidification, MLF induction or prevention, SO2 additions, and cold stabilization timing.

• Titratable acidity (TA): expressed as g/L tartaric acid equivalents; desirable range for table wines is approximately 5.5 to 8.5 g/L
• Volatile acidity (VA): measured by Cash still or enzymatic analysis; aroma detection threshold for acetic acid is approximately 0.6 to 0.9 g/L in red wines
• Malic acid monitoring: enzymatic kits or HPLC chromatography track MLF progress; a result below 0.1 g/L indicates MLF is essentially complete
• pH measurement: essential alongside TA for assessing microbial stability, SO2 management, and predicting tartrate precipitation risk