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Refractometers are Fantastic: Why and How you use a Refractometer

Written by Janice M on . Posted in Hygiene & Quality Control, Technical Tips

What does a Refractometer / Brix Meter do?

A refractometer is an instrument that measures the amount of light refracted in a gas, liquid or substance. The refractive index is a measure of how much the speed of light is reduced. For example in a sugar solution, the light bends and we can look through a magnifying eyepiece and see how much it bends! The refractive index becomes higher in matter that has a higher concentration. This is best explained by means of a diagram.

A refractometer is also known as a “brix meter” or “density meter”.

Who invented the Refractometer?

Professor Adolf Brix, a German Chemist, invented the Brix Refractometer in 1854. Winemakers could not predict which grape juice would make the best wine and he invented a machine that measured the density of plant juices. He was honoured by having the measuring process named after him.

This was followed by the invention of the Laboratory Refractometer by Ernest Abbe in the late 1800s.

abbe_refractometer

Ernest Abbe developed this more precise refractometer whilst working for Carl Zeiss and it looks similar to a microscope – modern Abbe laboratory refractometers are very similar in appearance!

Digital refractometers were developed in late 1970, these removed the potential error with the human eye. Further advancements included the ability to measure multiple wavelengths, use of the Peltier effect for heating and cooling and software for recording results.

Pictured: Abbe refractometer with temperature-controlled prisms
Credit: Harvey W. Wiley (editor) Page 131 of Bulletin” by the U.S. Bureau of Chemistry

What is Brix?

Brix is most frequently used measurement scale for refractometers.

The brix is the number of grams of cane sugar dissolved in a cane sugar solution. When measuring a different dissolved substance, a conversion chart is used.

When measuring solutions that have more than one ingredient, the Brix will equal the total concentration % of all dissolved substances, eg sugar and mineral ions.

Why Measure Brix?

With many products, it is useful to know the density of a substance, such as in irrigation water, plant sap, milk and blood.

Plant sap contains energy-rich carbohydrates (sugars). Having a high level of plant sugars in a plant will mean that it has great flavour and goodness. The brix level is one of the most important tools that will tell us that the plant (fruit / vegetable) is of high quality. A high brix level also indicates a high mineral and nutrient level.

For example, a grape with a brix of 8 or less will be poor and sour tasting. A full flavoured, highly nutritious grape may have a brix of 24.

Brix Chart

Dr Carey Reams, an agricultural engineer, developed the Brix Chart for fruit and vegetables.

He owned a large laboratory in Orlando, Florida, and advised farmers on higher quality food production. Farmers who followed his advice produced higher quality crops. He advised adding extra minerals to the soil, such as “soft” rock phosphate, poultry litter and high calcium lime. His lab experiments proved that plant quality correlated directly with the richness of the juice.

View Brix Chart

How to use an Atago analogue refractometer:

analogue_refractometer_usage

How to use an Atago digital refractometer:

5 Tips for Best Results:

  1. Follow the manufacturer’s instructions for calibrating the meter. This is important for an accurate reading.
  2. High viscosity samples will need a larger sample amount. When the sample spreads out completely between the daylight plate and the prism, this is the ideal amount.
  3. When measuring hot and cold samples , wait 20 – 60 seconds before pressing the START / OFF switch so that the temperature of the sample and the prism can approximate to each other.
  4. To clean, use a lint-free tissue to wipe the sample off the surface. If the sample contains oil, use isopropyl alcohol and water to clean the surface.
  5. Avoid storing the meter in direct sunlight or in a moist environment.

Types of Refractometers:

  • Analogue / Optical refractometers – simple handheld device that uses the human eye to view the % brix
  • Digital refractometers – handheld, easier to use with a digital display
  • Special scales – most samples contain substances other than sugar and the brix % equals to the total concentration of all dissolved substances in the sample. Refractometers with special scales can measure parameters other than sugar,eg PAL-ACID1 measures citric acid and PAL-WHISKEYmeasures ethyl alcohol. Here you need to have a pure solution as any other substance dissolved in the sample will affect the readings.
  • Abbe laboratory refractometers – larger with higher accuracy, frequently used for precise lab work and solids
  • Inline refractometers – used in factories, a sensor is placed inside a pipe or tank and this records the brix of the solution

 

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