Léonie Lebain
In the field of wines, spirits, or liqueurs, measuring density or specific gravity is a standard part of routine checks. There are several ways to do this, most notably using a hydrometer or an electronic density meter.
While the result sought is the same, the choice between these measurement methods depends on a set of needs and constraints. So, in which cases should you prefer a hydrometer, and when should you choose to use an electronic density meter?
The hydrometer: a simple and effective solution
A hydrometer is a weighted, graduated glass instrument that is submerged directly into the liquid to be weighed. Once it has stabilized, the water line indicates the value corresponding to the density or the quantity shown on its scale.
The temperature of the liquid must also be taken into account when taking measurements. Indeed, the density of a liquid varies according to its temperature. When the sample temperature differs from the hydrometer's calibration temperature (usually 20°C in the beverage industry), a correction based on conversion tables may be necessary to obtain the corresponding value.
Despite the development of electronic instruments, the hydrometer retains several everyday advantages:
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Calibration stability: In the absence of electronic components or measuring systems requiring regular adjustment, the hydrometer offers very high measurement stability over time when handled and maintained properly.
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High mobility: It can be used easily in the field, particularly in cellars, distilleries, breweries, or laboratories.
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Good longevity: Aside from accidental breakage, a hydrometer can be used for many years.
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Limited investment: It is an economical solution for reliable measurements.
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No maintenance: No electronic components, batteries, or power supply required.
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Few upkeep requirements: Requires only careful cleaning.
For many routine measurements, it thus offers a good balance of simplicity, cost, and efficiency.
When should you prefer an electronic density meter?
The electronic density meter offers other advantages and becomes particularly attractive when analyses are numerous and/or very frequent.
It is particularly suitable when:
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the volumes of available samples are small
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a large number of samples must be analyzed
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measurements must be carried out regularly
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reading and recording results need to be facilitated
Electronic density meters are available in portable and benchtop versions. Portable models are practical for routine field measurements, while benchtop models are intended for production or analysis laboratories and generally provide higher precision, compliant with official standards.
In both cases, the devices are equipped with temperature management systems (automatic correction for portable meters, Peltier effect to bring the sample to 20°C for benchtop meters).
For example, the DA135 portable electronic density meter offered by Dujardin-Salleron allows you to measure different quantities and display the result directly in the selected unit. It also features a memory to store the results.
Hydrometers and electronic density meters are therefore not necessarily mutually exclusive: the choice depends above all on the frequency of analyses, the volume of sample available, and the conditions of use.
An important criterion: knowing the MPE of the instrument
When choosing a hydrometer, the scale of the graduation may naturally catch your eye. However, it is not enough on its own to determine the measurement accuracy.
It is also important to check the MPE (Maximum Permissible Error) of the instrument.
The MPE corresponds to the maximum accepted deviation between the value indicated by the instrument and the reference value.
Thus, a finer graduation does not necessarily mean that the instrument provides a more accurate measurement. The MPE is therefore an essential element to take into account when choosing a hydrometer.
In the case of alcoholometers and hydrometers used in a regulated environment, legal metrology requirements may apply. At Dujardin-Salleron, certain hydrometer and alcoholometer references are supplied with a verification report, certifying the instrument's conformity with the model that has passed type examination. To learn more, read our article dedicated to hydrometry and legal metrology: "Hydrometry and legal metrology: what requirements for alcoholometers?"
Density and specific gravity: what is the difference?
The two terms are often associated, but they do not designate exactly the same thing.
Density (mass density) corresponds to the mass of a liquid for a given volume. It can, for example, be expressed in g/cm³, kg/dm³...
Specific gravity is a ratio and has no unit. In the case of a 20/20 specific gravity, it corresponds to the ratio between the density of the liquid at 20 °C and that of water at 20 °C.
This distinction is important for choosing an instrument and a scale adapted to the measurement sought.
Please note: a scale graduated in percentage volume of alcohol can only be read if the instrument is used in a hydro-alcoholic solution (a laboratory distillate, for example).
Which instrument should you choose?
For routine checks and when ease of use and cost are important criteria, the hydrometer remains a particularly suitable solution.
When analyses become very frequent, samples are numerous, or their volume is limited, the electronic density meter can provide more comfort and speed.
The right choice therefore depends above all on the use and needs of the laboratory, cellar, or distillery.
