Refractometers

A refractometer measures the refractive index of a liquid. This value changes depending on the liquid's composition. It can be used to calculate concentration, density, or sugar and salt content. Many models feature automatic temperature compensation (ATC), as the refractive index depends on temperature.

KERN offers different types of refractometers for a wide range of applications, from outdoor measurements to laboratory analysis:

✔ Analogue handheld refractometers
Compact, mechanically robust and ideal for mobile use, for example in agriculture, beekeeping or education. Many models feature automatic temperature compensation (ATC), making them particularly suitable for changing ambient temperatures.

✔ Digital refractometers
With a digital display and integrated ATC for precise measurements, including under varying temperature conditions. Ideal for laboratories, industry and on-site quality control.

✔ Specialised refractometers
Optimised for specific applications such as honey analysis, urine specific gravity measurement, coolant testing or alcohol content measurement. Models with multiple scales are also available.

Using an analogue handheld refractometer is straightforward and takes just a few steps. Clean handling is important.
✔ Clean the prism
✔ Apply a few drops of the sample
✔ Close the cover plate
✔ Hold the instrument towards a light source and adjust the focus if necessary
✔ Read the value at the boundary line
✔ Clean the prism after measurement

The following steps show how to use a digital refractometer correctly and obtain reliable measurement results.

✔ Switch on the device (battery-powered)
✔ Clean the measuring surface
✔ Apply a few drops of the sample
✔ Start the measurement at the press of a button
✔ Read the result on the digital display
✔ Clean the measuring surface immediately after measurement

The choice between an analogue and a digital refractometer primarily depends on the place of use, the required accuracy and ease of operation:

✔ Analogue refractometers

Advantages: robust, affordable, compact and independent of an external power supply

Typical applications: beekeeping, agriculture, mobile food inspection and education

Special feature: Many models already feature ATC (automatic temperature compensation), which is useful when ambient temperatures change.

✔ Digital refractometers

Advantages: high measurement accuracy, easy operation and fast digital readout

Typical applications: laboratories, production, quality assurance and field service with demanding measurement requirements

Additional features: automatic temperature compensation, multiple scales and easy cleaning

In short:

➤ Choose analogue when mobility and simplicity are the priorities
➤ Choose digital when precision and ease of use are particularly important

✔ Food and beverages (sugar content in juices, fruit and vegetables; lubricant testing)
✔ Honey production (moisture content in honey)
✔ Winemaking and brewing (sugar, alcohol and fermentation)
✔ Salinity measurement (NaCl content in water)
✔ Urinalysis (urine specific gravity, diagnostics)
✔ Industry and automotive applications (glycol concentration, battery maintenance and metalworking coolants)
✔ General refractive index measurement

Depending on the application, different measurement scales are available, sometimes combined in a single instrument.

✔ Brix scale: Sugar content in food and beverages
✔ Salinity: Salt concentration in aqueous solutions
✔ Specific gravity / density: For example, urine or industrial liquids
✔ Multi-scale models: Several measurement scales in one instrument

How readings are taken depends on the instrument type. It is important to follow the inspection and calibration instructions in the operating manual.

✔ Analogue: Read the value at the boundary line in the field of view
✔ Digital: Read the result on the display
✔ Check and, if necessary, adjust the instrument according to the operating manual
✔ Keep the prism or measuring surface clean

Regular cleaning and calibration are important for a refractometer to provide reliable, precise measurements over time.

✔ Maintenance

1. After each measurement, clean the measuring surface or prism with a soft, lint-free cloth.

2. Do not use aggressive cleaning agents or a jet of water.

3. Protect the instrument from extreme temperatures, impacts and moisture.

✔ Calibration

Analogue refractometers: Usually calibrated using distilled water or a reference solution

Digital refractometers: Calibration at the press of a button using a test liquid

✔ KERN factory calibration

On request, KERN & SOHN performs factory calibration using certified, traceable reference liquids.
This calibration is carried out under standardised conditions and provides a high level of assurance, for example for use in laboratories, the food industry or audits.

Suitable for quality management systems such as ISO 9001, HACCP and GMP.

ATC is particularly useful when ambient temperatures change because it automatically compensates for the effect of temperature on the refractive index.

✔ Yes: When the instrument is used at varying temperatures (10–30 °C), ATC automatically compensates for temperature changes
✔ No: In a laboratory with a constant temperature, measurements can be performed without ATC. A manual correction is required when temperatures fluctuate.

A honey refractometer is specially designed to display the moisture content of honey.

✔ Standard instrument for beekeepers
✔ Helps safeguard the quality and shelf life of harvested honey

A honey refractometer measures the moisture content of honey, a key quality factor influencing its shelf life.

✔ Excessive moisture increases the risk of fermentation
✔ Guideline range: 15–18% moisture (depending on the applicable quality requirements)
✔ An essential tool for professional and hobby beekeepers to assess the quality and shelf life of their honey harvest

* The stated optimal moisture content of honey (15–18%) is based on the quality guidelines of the German Beekeepers Association (D.I.B.), DIN standard 10752 and international standards such as the Codex Alimentarius FAO/WHO – Honey Standard.

A wine refractometer measures the sugar content of grape must.

✔ Helps determine the optimal harvest date
✔ Supports monitoring of fermentation
✔ Provides a basis for estimating potential alcohol content

Whether in the vineyard or brewery, refractometers are an essential tool for quickly determining the sugar content of grape juice (must) or brewing wort. These values provide information on grape ripeness, fermentation progress and potential alcohol content.

A wine refractometer measures sugar content in °Brix or °Oechsle; in brewing, °Brix (approximately °Plato) is commonly used.

✔ Checking grape ripeness or original wort concentration in brewing
✔ Monitoring fermentation
✔ Providing a basis for controlling alcohol content

The sugar content of brewing wort, also called the original wort concentration, is a key parameter in the brewing process. Refractometers measure this content in °Brix, a unit that is close to °Plato, which is commonly used in breweries.

Typical target values for brewing wort in beer production – measured with a refractometer:

The following overview provides guidance for quality control in breweries:

Beer style | Sugar content (°Brix) | Application / description
✔ Light / alcohol-free beer | 7–10 °Brix | Very low alcohol content, reduced calories
✔ Pilsner / Helles | 11–13 °Brix | Classic, lighter-bodied lager beers
✔ Wheat beer / Export | 12–15 °Brix | Fruity, aromatic and full-bodied beers
✔ Bock / Doppelbock | 16–20 °Brix | Stronger beers with higher alcohol content and a pronounced malt character

Note: °Brix and °Plato are often close in value for unfermented wort; their respective reference systems must be considered for precise calculations. A refractometer with a Brix scale is therefore also suitable for quality control in brewing.

** The stated °Brix values for different beer styles are based on the Brewers Association Style Guidelines, the technical guidelines of the European Brewery Convention (EBC) and specialist websites such as braumagazin.de and bierwiki.org. The approximation °Plato ≈ °Brix reflects common industry practice.

The sugar content of grape must is a key quality factor in wine production. Depending on the region and application, it is measured with a refractometer in °Brix or °Oechsle.

Typical target values for grape must in winemaking – measured with a refractometer:

The following table provides an overview of typical sugar content ranges for different wine categories.

Wine category | Sugar content (°Brix) | Sugar content (°Oechsle) | Application / notes
✔ Early harvest / table wine | 15–18 °Brix | 60–75 °Oe | Light wines, simpler styles
✔ Quality wine | 18–22 °Brix | 75–95 °Oe | Common ranges for many white and red wines
✔ Spätlese / Auslese | 22–26 °Brix | 95–110 °Oe | Late-harvest and sweet wines
✔ Beerenauslese / ice wine | 26+ °Brix | 110+ °Oe | High-quality, sweet speciality wines

Tip: For international applications, a refractometer with multiple scales (Brix/Oechsle/KMW) is recommended.

*** The target ranges for °Oechsle and °Brix values in grape must are based on guidance from the International Organisation of Vine and Wine (OIV), German wine legislation (Section 9 of the German Wine Ordinance) and information from winegrowers' associations such as VDP and DWV.

In industrial applications, refractometers allow fast, reliable analysis:

✔ Testing metalworking coolants, oils or chemicals
✔ Helping protect against tool wear
✔ Maintaining consistent quality
✔ Taking quick on-site measurements without a laboratory

Water-miscible metalworking coolants are used in machining and are mixed from concentrate and water. The correct mixing ratio is essential for machining quality, wear protection and the service life of tools and machinery.

A refractometer can be used to determine the concentration of the coolant emulsion quickly and easily on site. The measured refractive index is converted into concentration using a product-specific correction factor.

Example:
Reading: 4.0 °Brix
Correction factor: 1.5
→ Concentration = 4.0 × 1.5 = 6.0% – whether this is within the target range depends on the metalworking coolant used.

✔ Early identification of excessively high or low concentration
✔ Helping prevent bacterial growth, skin irritation or corrosion
✔ No need to wait for laboratory analysis – ideal for daily testing directly at the machine

Correct antifreeze protection is important for operational safety in vehicles, industrial equipment and heating systems. Antifreeze fluids are based on glycol-water mixtures (such as ethylene glycol or propylene glycol) and must be checked regularly.

A refractometer can display the freezing point directly in °C – quickly, reliably and without the use of additional chemical reagents.

Example:
The refractometer displays −38 °C – an illustrative reading; suitability depends on the required operating temperatures.
Whether the level of antifreeze protection is sufficient depends on the fluid used and the requirements of the system.

✔ Easy freezing-point checks, for example in automotive workshops, cooling circuits or heat exchangers
✔ Instruments with preset glycol scales are available (ethylene glycol, propylene glycol)
✔ No conversions required for readings on the appropriate scale – ready for on-site use