How to Interpret Titratable Acidity Results
Joy Ting
The titratable acidity (TA) of a juice or wine represents the sensory perception of acidity or sourness. Chemically, TA is the sum of all the free (dissociated) and bound (undissociated) protons in a solution. This measurement correlates to the total concentration of acid molecules in wine including the tartaric, malic, citric, lactic, acetic and succinic acids1,2. Based on how humans perceive acidity, the TA is a much better measure of how acidic your wine will taste than pH.
It is difficult to assess the acidity of grape juice due to the high concentration of sugar. Sweetness offsets/masks acidity (one of the reasons for residual sugar in German Riesling and hybrid wines made from cold regions). Titratable acidity gives us a quantitative measure of that acidity. This value can help winemakers make pick decisions and guide acid additions at harvest.
Titratable acidity can be measured without expensive equipment. All that is needed is a functioning pH meter, a burette, and some glassware (see protocol above). Though it may take a bit of practice, most winemakers can measure TA with a reasonable amount of precision and accuracy (see Dr. Howe’s webinar for more info). The real question is, what do you DO with the information once you have it? What is a “normal” TA value? What does it mean if TA is lower or higher than “normal”?
TA is dependent on vintage, variety, maturity, vineyard and winemaking practices1–3, leading to a wide range of potential values at harvest.
- Cooler vintages have higher TA (due to malic acid retention).
- TA decreases as grapes mature, so grapes that are picked early in ripening (ex: Chardonnay for sparkling) generally have higher TA than grapes that are left to hang longer on the vine.
- Some varieties also have higher TA. For example, Petit Manseng and Chardonnay at equal levels of Brix have very different titratable acidity levels. (Petit Manseng is higher.) Hybrid varieties like Vidal and Chambourcin also tend toward higher TA.
- Winemaking practices will also alter the TA of the wine. Skin contact in white varieties and skin fermentation in reds will decrease TA. Malolactic fermentation will also decrease the TA.
These all make it difficult to determine what “average” means or to make clear recommendations. However, the impact of TA on sensory properties remains the same, so it is important to know how your grapes compare. Some values reported in textbook literature include:
- 7.0 -8.0 g/L in white wines, 6.0 – 7.5 g/L for reds (Boulton 19991)
- 5.5 – 8.5 g/L with white varieties on the higher end of the range and red varieties on the lower end (Jackson 20142)
- 5.0 – 16 g/L with sparkling wine recommendations from 11-18 g/L (Zoecklein 19953, Zoecklein 20024)
In Virginia, these values are usually lower than reported in California and France. Juice and wine data from WRE experiments in 2014 – 2020 showed mean values of white wines between 6.4 g/L and 7.3 g/L, though these ranged from 3.9 – 12.6 (Table 1). High TA values in Chardonnay were likely due to fruit picked for sparkling wine while the lower TA samples in Petit Manseng were due to extensive skin contact in one experiment. Titratable acidity in Cabernet Franc and Merlot were much lower, with average TA of 4.2 - 4.5 g/L. The average TA at harvest in Petit Verdot was much higher (7.2 g/L). The caveat with Petit Verdot is that this variety usually contains high levels of potassium in the skins that drive down TA and drive pH up) during fermentation. In addition to averages, the ranges were quite wide for all varieties (Figure 1).
Table 1: Titratable Acidity at Harvest for WRE Samples 2014-2020
The take-home message is that measuring TA provides a fuller picture of the sourness of the wine after fermentation. Very low values will lead to wines that are flat while very high values may lead to wine that is sharper than desired.
References
(1) Boulton, R. B.; Singleton, V. L.; Bisson, L. F.; Kunkee, R. E. Principles and Practices of Winemaking; Springer US: Boston, MA, 1999.
(2) Jackson, R. S. Wine Science: Principles and Applications, 4 edition.; Academic Press: Amsterdam, 2014.
(3) Zoecklein, B.; Fugelsang, K. C.; Gump, B. H.; Nury, F. S. Wine Analysis and Production; Springer: New York, 1995.
(4) Zoecklein, B. W. A Review of Methode Champanoise Production. Virginia Cooperative Extension 2002, No. Publication 463-017W.
