Alcohol content in beverages: determination methods and calculations

Have you ever wondered how the alcohol content of drinks is determined? This calculation is not always easy, as there are usually many other substances in the drink, such as sugar, which can interfere wtih the measurement process. However, as the alcohol content on bottles must be stated to the nearest 0.3% vol. by law, various methods have been developed to check the alcohol content precisely. In this article, we present common methods for determining the alcohol content and explain how you can calculate the alcohol content and the amount of alcohol consumed.

Legal requirements for the indication of alcohol content

The exact indication of the alcohol content on drinks bottles is required by law in order to provide consumers with clear information about the alcohol content and to promote responsible consumption. In the European Union, the alcohol content must be stated to the nearest 0.3% by volume. This requirement is intended to ensure that consumers know how much alcohol they are consuming. National authorities, such as the Federal Ministry of Food and Agriculture (BMEL) in Germany and the food control offices of the federal states, are responsible for monitoring and ensuring compliance with these regulations. These authorities carry out regular checks to ensure that the information on the labels is correct.

The different measurement methods for alcohol content

Determining the alcohol content in beverages is an essential part of quality control in the beverage industry. Different measurement methods offer different advantages and disadvantages in terms of accuracy, effort and range of application. Here are the most common methods for determining the alcohol content:

Alcohol determination using a hydrometer

A hydrometer can be used to determine the alcohol content by measuring the density. This device, also known as an alcohol meter, works according to Archimedes' principle. For liquids with few foreign substances (such as vodka or grain), the sample can be poured directly into a standing cylinder and the alcohol meter immersed. The alcohol content can then be read directly from the scale. As the alcohol meter is calibrated to 20°C, a temperature correction may have to be made.

Determination of the alcohol content using steam distillation

A quick method for large companies is alcohol determination using steam distillation. Highly heated steam is passed into the sample, which shortens the distillation time. The alcohol content is then determined using an alcohol meter. For more precise results, an oscillating U-tube can be used, which measures the density more accurately but is significantly more expensive.

Enzymatic alcohol determination (UV test)

A very precise method is the detection of ethanol using a photometer. The sample is diluted and the ethanol is enzymatically converted into NADH with the addition of various substances, which can be determined using the photometer. The photometer measures the light absorption of the NADH, from which the ethanol content is calculated.

Total alcohol determination using a pycnometer

The official reference method for determining alcohol is pycnometry. The sample is first neutralized to remove interfering acids and then distilled. The mass of the distilled alcohol is then compared with the mass of distilled water to calculate the alcohol content. This method requires a high degree of accuracy and patience, as the measurements must be accurate to the fourth decimal place.

Calculate alcohol content: From percent by volume to gram

The alcohol content of all alcoholic beverages is indicated in percent by volume (vol%). This information refers to 100 ml of the drink. A 15% alcoholic drink therefore contains 15 ml of alcohol in 100 ml. To calculate the amount of alcohol consumed and the alcohol content, the alcohol content must be given in grams. As alcohol has a lower density than water, 1 ml of alcohol corresponds to approximately 0.8 grams.

Sample calculation

Let's take a 15% alcoholic drink: 

• 15 ml alcohol in 100 ml drink. 
• Converted into grams: 15 ml x 0.8 = 12 g. 
• This means there are 12 grams of alcohol in 100 ml of the drink.

Tables for converting percent by volume to grams

Calculation of the promille content in the blood

The blood alcohol content indicates how much alcohol is present in the blood and is measured per mille (‰). It is an important indicator for estimating the impairment of driving ability and the risks of alcohol consumption. To calculate the blood alcohol content, the amount of alcohol consumed in grams is divided by the body weight in kilograms and the distribution factor (0.7 for men and 0.6 for women). Here is a simplified formula:

For Men:
Consumed pure alcohol in grams
------------------------------------------------------- = Blood alcohol content
Body weight in kg x 0.7

For Women:
Consumed pure alcohol in grams
------------------------------------------------------- = Blood alcohol content
Body weight in kg x 0.6

For example: A person weighing 70 kg who has consumed 20 g of alcohol would have a blood alcohol content of:

20
------------- = Blood alcohol content -> 0.41‰
70 x 0.7

A blood alcohol content of 0.5‰ can significantly impair driving ability, and in many countries, 0.8‰ is the legal limit for driving under the influence.

Influence of sugar content and other substances on alcohol determination

The sugar content and other ingredients in drinks can influence the determination of the alcohol content and lead to inaccurate measurements. Sugar increases the density of the liquid, which can lead to higher apparent alcohol contents when measuring density with a hydrometer or pycnometer. Therefore, such samples often need to be treated beforehand to remove or neutralize the sugar. In methods such as enzymatic alcohol determination and steam distillation, the influence of sugar and other substances is minimized as these methods are specific to ethanol. Nevertheless, it is important to prepare the sample correctly and choose the right method to obtain accurate results.