August 2009 Issue of Wines & Vines

Shopping for Refractometers

Portable, digital models accurately measure in the vineyard

by Paul Franson
Most winegrape growers use refractometers to measure the amount of sugar in juice, but technically the instruments calculate how quickly light travels through liquid, compared to water.


  • Even grapegrowers who make harvest decisions based on taste seek assurance from a good refractometer.
  • Work in the vineyard or winery doesn't always happen under lab conditions. It's important that your refractometers are well built and a reasonable size.
  • Novice users often find it easy to use digital devices.

Although many modern winemakers proudly tell the media that they don't depend on "numbers," and prefer to taste the grapes to determine whether they're ready to pick, it's a rare one who doesn't also check the chemistry. Sugar readings, as well as pH and acidity, provide valuable information, particularly when combined with tasting the grapes and observing their color and condition, as well as that of the seeds and stems.

Knowing initial Brix is also important in future monitoring of fermentation and in estimating alcohol content.

The first step in harvest for most growers and winemakers is to sample Brix, and relatively new digital refractometers can make the task even simpler and more accurate than traditional optical analog models. They're not much more expensive, either, thanks to the wonders of modern electronics technology. Still, some winemakers prefer the old-fashioned way--some citing inconsistencies and lack of correlation to their traditional tools.

Analog or digital, a refractometer is an optical instrument that measures the density of water-soluble materials, i.e., the proportion dissolved in the water as a ratio. It measures the refractive index, which is the speed at which light passes through a liquid: The denser the liquid, the slower the light will travel through it, and the higher the reading will be on the refractometer. The unit may include refractive index (RI), but it is surely calibrated in a more useful scale, such as Brix, specific gravity, Baumé or other scales in some countries.

Traditional optical refractometers are compact and easy to use in the vineyard with almost no training--although they're only accurate at one temperature, so a correction must be applied for testing grapes in other temperatures.

Refractometers designed for field use are usually rugged and easy to use. They only require a few drops of liquid--certainly less than is contained in a single grape--for testing sugar content.

Digital refractometers depend on the same optical property of solids and liquids dissolved in water, but they incorporate a light-emitting diode and optical sensor as well as analog-to-digital conversional electronics to provide a more accurate and precise reading. They can conveniently incorporate calibration and temperature compensation. They're also easy to use, and even unskilled users can get consistent readings of the same sample.

Various scales for measuring sugar in must

Edited by Misco Inc. and listed in order of date developed:

: Developed by a French pharmacist in 1768, the Baumé scale was designed to make hydrometers easier to read. The method uses two separate hydrometers and is used mostly in France.

: The Twaddell hydrometer, developed in England between 1812 and 1839, consisted of a series of spindles with graduations from 0 to 174. It is still in use in England and some former English colonies.

Gay-Lussac Scale (°GL): Invented between 1798 and 1850, the GL scale was used to measure percent of ethanol by volume. It is the same as the Tralles scale but measured at 15°C (59°F).

Tralles: Like the Gay-Lussac scale, the Tralles scale was a hydrometer scale designed for reading percent ethanol by volume. It found usage with customs officials primarily in the U.S. and Germany.

Öechsle Scale (°Oe): The Öechsle scale was invented in Pforzheim, Germany, in 1836. It is used predominately in Germany and Switzerland to measure ripeness of grapes or the sugar content in must.

Balling: The Balling hydrometer scale was developed by a German chemist in 1843 to measure the concentration of a sucrose solution. The scale is used in the South African wine industry.

Plato: Fritz Plato developed this scale as an improvement to the Balling scale. It is used mostly by European beer brewers.

Brix: Austrian Adolph Brix developed the Brix scale for measuring sugar concentration between 1850 and 1870. Brix has become the defacto standard in the U.S. and most the world.

Klosterneuburger Mostwaage scale (KI°, °KMW, Babo): Baron August Wilhelm von Babo introduced the KMW scale in Klosterneuburg, Austria, in 1861. It was later adopted by the Italians and is called the Babo scale in Italy. P.F.

As any grower and winemaker knows, however, sampling methods can have a large impact on readings, particularly with the small samples employed in refractometers. Sugar content can differ significantly in different parts of a vineyard, in clusters on a vine, and even among grapes in a cluster. It's common for readings taken in the field to differ by a few degrees Brix from those of must samples taken from vats at a winery.

Opinions about sampling methods differ somewhat--from random berry samples around a vineyard, to strict numeric berry sampling, to choosing and pressing whole clusters at various locations. Certainly, full readings should be performed on the crushpad to correlate with field readings. This is especially true if you're using uncompensated analog instruments, which provide only an estimate of the sugar level in most cases.

Hints for use

• Use temperature-compensated instruments or apply correction.

• Clean instruments well before use to remove any potential residue or contaminants.

• Calibrate with plain water before use.

• Clean instruments well after each use.

Wines & Vines asked major manufacturers of refractometers to recommend their most popular hand-held, portable instruments for wine applications. Many resellers offer these and other instruments, including similar analog refractometers; some are sold at very low prices.

Typical analog refractometers
Misco economy refractometer: The Misco economy import ECO7113 refractometer offers a low-cost alternative to the company's premium refractometer product line. These refractometers are ideal when cost is more important than durability, accuracy and precision. The company claims, "If all you need is a quick ballpark reading, then our new economy refractometer is right for you." Price: $125.

Reichert Rhino handheld refractometers: Reichert produces the Brix Rhino series of hand-held refractometers in three ranges, one (0-30) suitable for most winemaking applications. It reads in the Brix scale or percent solids (as sucrose). The instrument is now produced in a black, impact-resistant polymer housing with double-cemented glass optics for ruggedness. It is IP 67 dustproof and water-resistant. It claims improved image quality and a blue prism for improved scale and reading visibility. It also includes automatic temperature compensation. Price: about $125.

Digital refractometers
Atago Pocket PAL-1 digital refractometers: The Atago Pocket PAL-1 digital refractometer is lightweight and compact, and it has a range 0°-53°Brix. Other models have other ranges. It meets IP65 water resistance standards and can be washed by simply holding it under a faucet. It includes automatic temperature compensation and an electroluminescence technology display that can be read both outdoors and indoors. It can be calibrated with tap water. Suggested price: $295.

Hanna HI 96801 Digital Refractometer: The HI 96801 Digital Refractometer is a rugged, portable, water-resistant device that's a little larger than some other portable units. Samples are measured after a simple user calibration with de-ionized or distilled water. The HI 96801 is able to read samples as small as two metric drops. The instrument measures the refractive index of the sample and converts it to °Brix concentration units. Temperature (in °C or °F) is displayed simultaneously with measurement on the large, dual level display along with other helpful message codes. The HI 96801 is operated by a single 9-volt battery with a life of 5,000 readings; it is waterproof to IP65 standards. Dimensions are 19.2cm x 10.2cm x 6.7cm. Suggested price, $185.

Mettler-Toledo Quick-Brix 60: Quick-Brix 60 is a compact, portable digital Brix meter that fits into any coat pocket. It's rugged and, thanks to its splash-proof design, it can be rinsed off for cleaning. Squeeze juice onto the prism, press the read key and get the result. Wipe the prism with a tissue for cleaning and calibrate with a single keystroke and water as standard. It measures Brix in the range from 0º to 60º with a resolution of 0.1º Brix and an accuracy of ± 0.2%. Built-in temperature compensation always converts results to a standard temperature of 20°C. Its usable temperature range is 10°C-70°C. Dimensions are 43mm X 26 mm X 170 mm. The weight is 420g. The price is $407.

Misco Palm Abbe handheld digital refractometers: The Misco Palm Abbe line of hand-held digital refractometers is engineered specifically for the international wine industry. They provide instant digital field determination of grape ripeness, grape-must concentration and density, sugar content, and the potential and actual alcohol content of the finished wine. Certain models display prompts and measurements in English, Spanish, French, German or Russian. Other models are available with scales for various international units of measure. Users have the flexibility to mix and match up to five different scales on some Palm Abbe models. Protection against inaccurate readings due to temperature differences is assured with nonlinear temperature compensation specific to grape juices, and is automatic for fluids reading between 0°C and 50°C (32°F to 122°F). A simple interface consists of two buttons: one to take readings and the other to step through menu options. A large, dual-line, multilingual LCD display is visible even in dim light. Calibration of the Palm Abbe is automatic and does not require special calibration solutions or tools; it automatically calibrates itself to water. The PA201 calibrated in Brix is $325.

Reichert R2mini Digital Refractometer: Reichert claims its R2mini is the world's smallest pocket digital refractometer offering optimum performance. Its measures both ºBrix and Refractive Index. The range is 0º to 62.0º Brix, and 1.3330 to 1.4465 RI with an accuracy of 0.2º Brix and 0.0002 RI. It features automatic temperature compensated measurements. Readings are displayed on a five-digit LCD screen. It's housed in a durable case with non-slip side grips and is rated IP65 dustproof/water resistant for use in any environment. Two AAA alkaline batteries power more than 10,000 measurements. Dimensions are 5.4cm x 2.7cm x 10cm, and it weighs 100g. The price is $195.

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