How to measure the total and volatile acidity of wine

When it comes to wine, acidity plays a crucial role in determining its overall taste and quality. Two important measurements that help determine the acidity of wine are the total acidity and volatile acidity. Total acidity refers to the overall acidity level of the wine, while volatile acidity measures the presence of specific volatile acids that can impact the wine’s flavor. In this article, we will explore how to measure the total and volatile acidity of wine.

Total Acidity Measurement:
Total acidity is typically measured in terms of tartaric acid, which is the primary acid found in grapes. To measure the total acidity of wine, the most common method is through titration. Here’s a step-by-step guide on how to measure the total acidity of wine:

1. Prepare the Solution: The first step is to prepare a solution of sodium hydroxide (NaOH) with a known concentration, usually around 0.1 normal (N) or 0.1 molar (M). This solution will be used as the titrant to neutralize the acid in the wine.

2. Wine Sample Preparation: Take a sample of the wine and place it in a beaker or flask, ensuring there are no visible impurities or sediments.

3. Indicator Selection: Add a few drops of an indicator, such as phenolphthalein or bromothymol blue, to the wine sample. The indicator will change color once the acid has been neutralized.

4. Titration Process: Slowly add the sodium hydroxide solution to the wine sample while stirring continuously. The sodium hydroxide will react with the acid in the wine, causing the color of the indicator to change.

5. Determining Endpoint: Continue adding the sodium hydroxide solution until the color of the indicator changes permanently. This color change indicates that all the acid in the wine has been neutralized.

6. Calculation: Determine the amount of sodium hydroxide solution used in the titration. This value, along with the known concentration of the solution, can be used to calculate the total acidity of the wine in grams of tartaric acid per liter (g/L) or millimoles of tartaric acid per liter (mmol/L).

Volatile Acidity Measurement:
Volatile acidity refers to the presence of certain volatile acids, primarily acetic acid, in the wine. High levels of volatile acidity can result in undesirable aromas or flavors, such as vinegar-like or nail polish remover-like notes. Measuring volatile acidity requires a slightly different approach compared to total acidity. Here’s how to measure the volatile acidity of wine:

1. Distillation: Distill a sample of the wine using a distillation apparatus, such as a Clevenger apparatus. This process helps separate the volatile components, including volatile acids, from the non-volatile components.

2. Collection: Collect the distillate, which will contain the volatile acids, in a receiver flask.

3. Neutrality Check: Add a small amount of sodium hydroxide solution to the distillate and mix it well. The presence of volatile acids will cause the solution to become turbid due to the formation of precipitates.

4. Titration: Perform a titration using a sodium hydroxide solution of known concentration, similar to the process used to measure total acidity. The sodium hydroxide will neutralize the volatile acids present in the distillate.

5. Calculation: Calculate the volatile acidity in grams per liter (g/L) or millimoles per liter (mmol/L) using the amount of sodium hydroxide solution used and its known concentration.

By measuring the total and volatile acidity of wine, a winemaker or wine enthusiast can gain essential insights into the wine’s flavor profile and quality. Understanding the acidity levels allows for adjustments during the winemaking process to achieve a balanced and desirable product.