Breaking down the pros and cons of optical and digital refractometers for use in the food industry.

Most commonly used in the food and beverage industry to measure sugar (°Brix), a refractometer tracks an optical constant and uses this information to reveal characteristics of the materials it is testing. Put simply, the speed of light is constant when recorded in a vacuum, but decreases whenever it passes through a material. The ratio of these two speeds is the optical constant known as the refractive index.  

Although it’s interesting to think about the science behind this process, refractometers save you the trouble of thinking too hard. Instead, you can rely on this ingenious piece of kit to reveal everything from sugar and salinity levels to glucose and fructose. You can also focus your attention on choosing between an optical and digital refractometer – using our honest comparison to weigh up your options. 

On the subject of honesty, we wanted to be upfront about the fact that Klipspringer supplies both optical refractometers and digital refractometers. With this in mind, we have endeavoured to be as unbiased as possible – drawing on our 22 years of experience and sharing only the most relevant insights. Our goal is always for you to make the right decision for you and your site, and we hope this overview helps to make this possible. 

Optical Refractometers

First, let’s consider the benefits of an optical refractometer. With a durable rubber grip, replaceable prism flap, and a well-balanced design that sits in the palm of your hand, this robust piece of equipment is suited to the daily demands of factory life. It is also IP65 water resistant and doesn’t require any batteries or power source.  

Recognised by operatives across the country and favoured by workers who have a tentative relationship with technology, optical refractometers are a tried and tested solution. This model is a great fit for simple factory applications, as it can measure within an extremely specific range. Measuring a more significant range proves to be a problem though, with many factories having to purchase multiple units to cover the ranges relevant to their processes.  

At Klipspringer we provide optical refractometers that work within the following parameters: 

Unlike a digital refractometer, it isn’t possible to purchase an optical unit that covers 0-95%. This is because as the range of an optical refractometer increases, it becomes more and more difficult to secure accurate results. With optical refractometers already open to human error, this is a risk that factories can’t afford to take.  

Instead of benefiting from the clear LCD display of its digital counterpart, the optical refractometer must be read by an operator through an eye piece that is held up to the light. Although this is a fairly straightforward process, there is always the possibility of results being impacted by an operative that has poor vision, doesn’t fully understand what they’re looking for, or is rushing through their duties. By comparison, the digital refractometer takes two seconds to display an accurate reading that doesn’t need to be interpreted.

Digital Refractometers

In recent years, we have seen a major shift towards digital refractometers, with the possibility of optical models being phased out entirely. This is because units such as the OPTi Digital Handheld Refractometer not only cover the full 0-95 Brix scale in one unit, but also boast an onboard library of 50 common scales. These scales include: 

  • °Brix 
  • Fructose 
  • Glucose 
  • Maltose 
  • Invert Sugar
  • Total Solids of Waste Milk
  • Salinity (NaCl) 
  • °Butyro 
  • Mass Sugar (°Brix) 
  • Alcohol Probable (AP) 
  • °Baumé
  • °Plato

This digital monitor also allows you to pre-set up to three scales, empowering your operatives to move between, for example Brix, Alcohol Probable, and Fructose, with just the touch of a button. This should result in huge savings on time and effort. It will also allow you to de-skill this aspect of your operation, as workers of all abilities will be able to easily operate this piece of kit. 

The key point that could cause a factory to hesitate before investing in a digital refractometer is the slightly higher price point. There is also the ongoing cost of replacing the unit’s batteries. Even with this in mind, we’ve found that once a technical manager considers the time saving benefits of a digital refractometer, they can identify the long-term savings.

Another factor that informs their decision making is the fact that digital refractometers cover the full 0-95 Brix scale. This allows them to purchase just the one unit, as opposed to multiple optical versions. Finally, with 10,000 readings provided by two AAA batteries, this small expenditure doesn’t undermine the overall benefits.  

Key Points to Consider

Digital Refractometers:

  • Increased accuracy 
  • Durable IP65 rated body 
  • Read time of two seconds per sample 
  • 10,000 readings on two AAA batteries 
  • 50 scales available 
  • Option to pre-set three different scales 
  • Full 0-95 Brix range (and 1.33-1.53 RI) 
  • Stainless steel prism dish to stabilise sample temperature 
  • Slightly higher price point 
  • Additional cost of batteries and calibration 

Optical Refractometers:

  • Smooth eyepiece adjustment 
  • Well balanced in the hand 
  • Durable rubber grip 
  • Replaceable prism flap 
  • IP65 water resistant 
  • No need to replace batteries 
  • Open to user interpretation 
  • Less accurate 
  • Limited range 
  • Additional cost of purchasing multiple refractometers to cover multiple ranges 

Benchtop Refractometers

Depending on the specific needs of your factory, it might be that you are in need of a Benchtop Refractometer. When compared to Handheld Refractometers, Benchtop Refractometers tend to offer more accurate results, increased durability, a more extensive method system, and a larger memory capacity.

Here at Klipspringer, our range of Benchtop Refractometers include the RFM732-M, the RFM 742-M, the RFM 340-M, and the RFM 340-T,

Key features of a T-Series Refractometer include:

  • High-definition touchscreen display that can be used with PPE gloves
  • Dual display function allows two different scales to be displayed simultaneously
  • Over 20 pre-programmed scales including Brix and RI
  • Option to programme up to 100 user defined scales using a PC
  • Method system allows for limit checks against stored data and product-specific corrections
  • Precision engineered flat, easy-clean prism for fast, accurate readings
  • Prism with large sampling area – allows for measurement of difficult to read samples such as fruit juice, pulps, sauces, and industrial resins
  • Peltier Temperature Control (Automatic Temperature Compensation), plus SMART temperature stability to ensure results show only once the sample is stable
  • Storage for over 8,000 readings
  • RFID User Clearance, electronic signatures, and audit trails
  • Enhanced functionality via the USB interfaces: back-up, clone, and print to secure PDF formats
  • Option to display the on-screen menu in several languages

RFM340-T:

  • Increased measurement performance between 0-30 °Brix. By improving the performance at the low end of the scale, potential errors are reduced in the critical range for juices and sodas. It will also allow you to reduce syrup dilution to the absolute minimum without breaching manufacturing specifications.

Key features of an M-Series Refractometer include:

  • Over 20 pre-programmed scales including Brix and RI
  • Option to programme additional scales
  • Peltier Temperature Control (Automatic Temperature Compensation), plus a time delay before reading to ensure reliable and stable results every time
  • Artificial sapphire prism mounted in an easy-clean stainless-steel dish with a PEEK spill barrier and an outer-barrier that is sealed and shaped to withstand moisture ingress
  • LED light source for over 100,000 hours of use
  • Tactile, alphanumeric keypad
  • Classic red or modern colour display
  • Enhanced functionality via the USB interfaces: save and print to CSV or secure PDF formats
  • Multiple scale Audit trail (date, time, batch, and operator)

RFM340-M and RFM742-M:

  • Higher resolution that is ideal for use in beverage, dairy, and confectionery manufacturing.

Calibration and Verification

When it comes to purchasing a new piece of equipment, it is always worth considering the calibration or verification process. After all, every unit needs to be calibrated or verified to some extent. Even Optical Refractometers, which can’t be adjusted, still need to undergo a Calibration by Comparison. This is the process of comparing the results of your refractometer to the relevant reference standards to see if it is functioning correctly.

Here at Klipspringer, all the refractometers we supply can be calibrated and the most common interval for this process is 12 months. We have also launched a series of calibration materials that allow you to carry out at least some of your calibrations remotely. In addition to this, we now stock a range of solutions that give you the option of validating your refractometers on site.

The expectations are different for every site, but as a general rule, we recommend calibrating your refractometers with distilled water before every use, if not weekly.

That brings us to the end of our honest comparison of optical and digital refractometers. When it comes to evaluating the pros and cons of each option, the most important thing is that you prioritise the specific requirements of your factory. After, all nobody understands your site better than you! However, we do hope this overview has been a useful resource – helping you to evaluate the risks and applications associated with either purchase.  

With around 22 years of experience supporting over 4,000 food and beverage sites across the UK and Ireland, we are always happy to share our honest feedback and findings, determined to assist you in making the best decision for you and your site.

If you would like further guidance relating to your refractometer requirements, the Klipspringer team would be happy to help. Share your details below to arrange a free consultation.