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How to use a refractometer

Last Updated: 13.07.20

Refractometers are commonly utilized to measure the concentration of liquids. They can be used under an array of circumstances and in multiple settings, and that’s why we have decided to write this article and let you know how you can make the most of them depending on your application.

In a nutshell, a refractometer is an optical device just like the binoculars from this review are. It can somewhat be compared to a hydrometer and you can use it to measure the specific gravity of urine if you work in a laboratory, or of wort or beer, if you brew your own beverages. Unlike a hydrometer, such a gadget is more compact and, to some extent, easier to utilize. You only need several drops of the aqueous solution to determine its concentration.

There are several varieties of refractometers available out there, which is why we suggest you perform a refractometer comparison before choosing a particular model. Some come with their own light source while others depend on an external one in order to do their job. Most of those that rely on an external light source are more or less inexpensive, so you should consider them if you’re on a tight budget.

When it comes to letting you know the density of the aqueous solution you want to measure, most refractometers will let you know the reading either in Brix or RI, with the second standing for Refractive Index. Because word doesn’t have the same reflective properties as water to which you have added sugar, you need to utilize a formula in order to convert either the RI or the Brix index.


How to calibrate a refractometer

Calibrating such a device isn’t all that difficult, but you do need to use distilled water. Place several drops onto the sample plate and close it so as to allow the water to spread across the surface. There should be no bubbles as they can impact the result.

Most of the models that we have come across are temperature-sensitive, and what that means for you is that you should always make sure that the sample has reached room temperature before attempting to measure its concentration. Of course, there are several alternatives that can compensate for temperature if they’re automatic, but they do cost a pretty penny compared to those that don’t come with this feature.

Take the reading by holding your refractometer up to natural light. If you’ve used distilled water, as we have noted above, you should use the screw or the knob that the unit is outfitted with so as to adjust it to read zero.

If you intend to utilize the device for getting the density of wort, we recommend performing two measurements. One of them should be with distilled water and the other with wort whose specific gravity you know for sure. To do this, you can first get the wort reading using a hydrometer and then match it to that offered by the refractometer.

How to use a refractometer for beer brewing

Using the device per se is more or less simple as it resembles the calibration process that we have depicted above. Start by making sure that the sample plate of the refractometer is both dry and clean, and then add several drops of the wort that you want to use. One note that we have to make in this respect is that the temperature of the wort should not be higher than 68F so as to avoid getting inaccurate readings.

All you have to do then is close the plate, make sure that you check for bubbles, and then hold the device up to a light source. It is preferable to utilize a natural light source as it can help you get accurate results. The reading that you will take from the sight scale can be expressed either in a percentage or degrees depending on the scale you will use — Brix or RI.

Understanding that the gravity of the alcoholic beverage you are making differs depending on its fermentation level is the right way of going about things if you do not intend to be disappointed in your refractometer.

You’ll have to calculate the results either by using a spreadsheet or a specific tool. Keep in mind that the equation changes as the fermentation progresses and more alcohol is produced.


Understanding the Brix scale

The Brix scale can tell you the concentration percentage of your sample. Every time you attempt to get a reading of a sugar solution, you need to make sure that the Brix percentage matches the actual concentration. For that, you will have to utilize a scale. Fortunately, it can be found online.

For instance, the % Brix for cutting oils range from 0 to 8 while that of carbonated beverages can range from 5 to 15. Jams and jellies have a % Brix concentration of 60 to 70 while that of grapes and wines ranges from 14 to 19.

Understanding Refractive Indexes

Unlike their Brix scale counterpart, Refractive index readings depend on the temperature of the environment. At 25 degrees Celsius, the refractive index of acetic acid, commonly known as vinegar, should be 1.370. At 20 degrees Celsius, the RI of olive oil should be 1.471.

As is the case with the Brix scale we were mentioning earlier on, you have a wide array of scales and references available online, and even several formulas that can help you get the concentration of your craft beer.


Make the most of online resources

If you still can’t figure out how to use your device, we suggest you go online and do extensive research on the topic. Luckily, there is a myriad of websites and video channels that you can make the most of. In fact, we’ve come across several YouTube videos that you can use to calibrate your refractometer.

Finally, if your application involves the production of homemade alcoholic beverages, don’t be afraid to use specialized forums and get in touch with other beer or winemakers like yourself.


Reading a refractometer

Since this type of device is a scientific tool for calculating the index of refraction of a liquid, there are some things you should know. Here, you will learn about the use of a sample and how the actual process happens. The measuring surface is practically a prism that allows the light to go through. The way the light refracts can give you some vital information on the composition of the liquid.

Distilled water is used as the baseline for calculating the index. Refractometers work within particular settings that are designed to help them serve specific purposes. That said, you can’t use a unit that was made for the specific gravity of, let’s say, seawater, for calculating the sugar content in a piece of fruit. Nonetheless, there are necessary steps for all refractometers in order for you to read them.

Your first step is to calibrate the refractometer, and you must do so with distilled water. This is the perfect solution as it will make sure that your prism is perfectly clean so that the liquid you need to examine is not contaminated in any way. Make sure that your device is placed horizontally, and then open the daylight plate.

Pour a few drops of distilled water on the measuring surface and then close the plate and keep it down so that the water distributes evenly. The next step is to point your device at a light source and then look through the eyepiece. You will immediately see a circular field and a line that’s created by the line that goes through. At the top, the circular field will be blue and white at the bottom. Your light line should be at the zero value of the index.

If that doesn’t happen, that means that some calibration, and you can do that by adjusting the eyepiece. Once calibrated, your refractometer is capable of reading the refractive index of the liquid you’re examining. To read the value, you will have to repeat the steps explained above when using distilled water. Make sure that you follow these steps with precision so that you can get more accurate readings possible.

Two drops are enough for calculating the refractive index. The light line now will be deviated and will point at a specific value on the internal index. Remember that the specific gravity for which the unit was built should be created for the type of solution you use for observation. Only this way, you can calculate the correct refractive index. In a nutshell, this is how you use this type of device.

How to use a refractometer to measure sweetness in fruits

You already learned earlier about the applications of a refractometer in beer brewing. But that’s not the only common application of this type of device. You can also successfully use one to determine the amount of soluble sugar so that you can tell how sweet the fruit is. The same method can be used for vegetables, as well, and the reason why you should be able to read such values is to determine the best time for harvesting.

In fruits, the level of sweetness should be between 5% and 15%, depending on various factors. For vegetables, the same value should be under 5%. Fresh and preserved products alike can be tested in this manner, a sample being taken from a larger quantity to determine its overall quality. This information can be used for establishing the market value, as well.

As you already know, a refractometer is pretty much a glass prism that comes equipped with a light source. The light must go through the sample, and the way it refracts gives the scientist running the experiment the information necessary for calculating the sugar levels. Such a measurement is required to determine whether the fruits and vegetables are ready to be harvested or not.

Without going into intricate details, you need to know that there is a correlation between the refractive index and the percentage of sugar present. This is just one of the many applications of refraction. The temperature under which the experiment takes place has an influence, too. The refraction is affected if the test is conducted outside the range of 68-86F. The reading will have to be increased with 0.5%SSC for every 10F above the required temperature.

The method is quite simple. First, you need to obtain a sample by cutting a wedge from the fruit in question, preferable from the stem to the core, and from the blossom to the center. Use a blender to crush, or, if you don’t have this type of equipment at your disposal, you can also use a mortar or a garlic press. Filter the liquid through a filter paper so that all the pulp, seeds and other solids are separated.

After that, you must follow several measurement steps. Check the prism for any scratches and stains. It must be spotless and free of such problems to function correctly. Should the glass be dirty, you should use a solution made from distilled water. Pour a few drops on the prism, shake it off, and then wipe it gently with a lint-free cloth.

With the help of a plastic pipette, pour a few drops of the liquid obtained on the measuring surface. Now you can observe it through your refractometer, but make sure that you have a light source, whether it is natural or from an incandescent bulb. Ideally, you should calibrate the refractometer before running your experiment. If everything is in place, now you need to twist the eyepiece until you have a clear image.

Read the value shown at the intersection of the contrast line with the scale. That should be the %SSC or Brix number of the sample. In other words, that is the concentration in % of the sugar content inside the liquid you obtained earlier. To make sure that the unit is ready for the next use, run a calibration by cleaning the measuring surface with distilled water.


Measuring the specific gravity of urine with the help of a refractometer

The refraction process can be used by medical laboratories, as well. While we explained how it could be used for brewing beer, we will now focus on other practical applications of this type of device. Urine has a refractive index, just like any different samples used for experiments. What matters is how the particles inside it can determine the light to refract, and that’s where a unit that can calculate the index at which it does so comes in handy.

For measurement purposes, you should use a model that was calibrated for calculating the index for urine, and not for other liquids. Once you have the correct device in your hands, it’s time to get to work. Place a couple of drops on the measuring surface. The plate must be placed on top and press so that there is no air trapped, and the urine is distributed all over the surface. This way, you will make sure that you will obtain an accurate reading.

Look in the device while keeping it pointed at a source of light. To make sure that the image you obtain is clear, see the adjustable screw that your model should come with. What the screw does is to move the bimetallic strip inside the unit, and that is how you calibrate the refractometer for accurate readings. Remember the step of using distilled water to clean the prism. That’s how you get a unit that’s ready to use.

The automatic temperature of your environment can influence your readings. No measurement is completely accurate unless you ensure that proper conditions are met. Refractors used by veterinarians usually come with 2 or 3 scales. The gravity of urine has a range of 1.000-1.030. But that’s not the only thing that these devices can calculate.

They can also calculate the protein levels present in a solution. Again, the process of refraction will be put to work. Another value that can be obtained with their help is the concentration of different solutions. As long as you abide by the rule of maintaining proper temperature levels, your experiment should run smoothly. However, you should know that not all clinical refractometers are capable of calculating all these values.

Before proceeding to examine urine with the help of this scientific tool, you need to make sure that it is properly calibrated, or, otherwise, any measurement you will take will not be accurate. The distilled water test should indicate a value of 1.000 on the SG scale. When you do that, ensure that the light line is right at the desired value; any small deviation could cause problems later on.

To calibrate the unit correctly, twist the screw and observe how the light line moves to the correct value of the SG scale. When that happens, you have a properly calibrated unit you can start using. Remember that the refraction is influenced by temperature, too, and make the required adjustments if that’s the case.


Other applications of a refractometer

A few applications of this scientific tool have been explained at significant earlier, but it is a good idea to be aware that there are multiple other areas that require the use of such a device.

–     Beekeeping

You might not expect to use such a tool in beekeeping, but it’s actually quite handy for measuring moisture in honey. Of course, the units that serve this purpose are explicitly designed for it, and they are called honey refractometers. Beekeepers use them to determine when the honey is ready for harvesting and has the desired characteristics to be stored. They also know about the importance of automatic temperature that can influence their readings.

And it is not all only about beekeepers wanting to identify the perfect moment for harvesting their honey. The content of water in honey is regulated by the FDA, and beekeepers need to make sure that they keep up with the industry standards, or otherwise, they might end up paying fines.

–     Winemaking

Although you will find plenty of references regarding the use of a refractometer for brewing beer, you should know that these tools are convenient for making wine, as well. The same steps must be followed, with a few drops of grape juice being poured on the measuring surface, and then examining the refraction of light so that you can take a proper measurement of the sugar content.

You need very little to determine if the grapes are ready to harvest so that you can obtain delicious wines. Wineries are all about automatic temperature adjusters so that the product they sell is adequate from all points of view, so there is no wonder that they use refractometers, as well.

–     Coffee making

A refractometer might not sound like the tool you would use for making coffee, but the bitter beverage that everyone loves can benefit from its measurement applications. Such a tool is ideal for measuring caffeine concentration in coffee. If you’re a barista who cares not only about serving clients with coffee at the right temperature but also with the proper amount of caffeine, this is an excellent solution.

You can vary the coffee recipes you make with the help of this device. To determine the amount of caffeine, you only need to pour two drops of coffee on the prism and then place the cover on top to make sure that the coffee got spread evenly, and there are no particles of air trapped inside.

The refraction of light that occurs will let you know where the concentration of caffeine falls on the index scale. Remember to get a model that was made specifically for calculating this value. You won’t be able to do this with a model created for examining saltwater, for instance. The good news is that there are reputable companies that make such refractometers, so your future as a barista is assured, without one shadow of a doubt.


How a refractometer works

Before we give you details on how to use a refractometer, it is essential that you understand how it works because you will be able to better understand the processes you have to go through while using it for different purposes. Optical instruments usually make use of how the light bends when it travels through different lenses made of glass. 

The refractometer is also an optical instrument and, although you can measure how light passes through a lens using it, you can also use it to measure how light travels through water and other liquids. As you probably know, when light rays go through water, the light bends these rays. 

Some of the light is reflected, which means that it goes back into the environment, but the light that travels through water is called refracted light. Normally, if the light would travel through the air, it would travel on a parallel and straight trajectory. 

However, because water or other transparent environments that light can travel through have different densities, the angle of the light modifies. This is why this optical instrument is called a refractometer because it measures the angle of the refracted light that travels through a certain transparent environment.

The degree at which light bends is dependent on the substance it travels through. If sugar is added to a substance, the light will have a higher bending level. This is how the refractometer detects the amount of sugar there is inside a liquid, by measuring how much the light bends.

Understanding the Brix scale

When we add sugar to water, depending on how much we add, we will see the effect that it has on bending light if we measure it using a refractometer. To make the measurement easier, the Brix scale was developed and the principle that it uses is very simple: 1 degree of Brix equals 1 gram of sucrose per 100 grams of solution.

This is pretty easy when we only have water and sugar, but when the substance we are measuring is combined with other ingredients, the Brix scale can only approximate.


Understanding Refractive Indexes

To better understand how to use a refractometer, you have to know the basics, such as what a refractive index is. As we have said before, some refractometers use the Brix scale and others use the RI, or refractive index scale. By using a refractometer that uses the RI scale, you will be able to analyze solutions that contain no sugar too, like saline solutions. 

A refractive index is a number between 1.3000 and 1.7000 for most composites and it has no measurement unit. The index of refraction depends on room temperature and the wavelength of the light. It is very important to control room temperature when we use a refractometer that uses the RI scale because room temperature can affect the refractive index.


How to use a refractometer to measure gemstones

There are lots of purposes for which you can use a refractometer and measuring gemstones is one of the most fun uses. Of course, that, as long as the gemstones are precious and as long as they are yours. No, we are just kidding, measuring how light travels through gemstones is really an interesting process. The result of the refractometer does not depend on the room temperature.

For measuring stones, you will have to use a refractometer that uses the RI scale. The highest measurement that a refractometer specially made for gemstones can make is 1.81. The downside is that you will not be able to measure the RI of a diamond, but you can spot if a diamond is fake because the refractometer will give you a value of less than 1.81.

If you have a refractometer that has an inbuilt lighting system, then it will most certainly have batteries as well. To be able to use it, you will need to turn the refractometer on. After you open the refractometer, you will see that there is a hemicylinder that has to be very clean before you start the measurements. So, if it has dust or dirt on it you should clean it using water and a soft cloth.

Before you examine the stone, you have to make sure that it is also clean of dust or fingerprints so a good practice is to clean it also, using a soft cloth. You should first make sure that it has a facet that is flat.

Now you will have to use an RI liquid to place on the hemicylinder, right on the upper part. You should use a small amount and don’t worry if you do not get the right amount from the first try, after you have been measuring several stones you will know exactly how much you should use. It should be just enough to make a seal between the hemicylinder and the stone you are measuring.

You have to place the stone with the facet on the drop of RI liquid and close the lid. If the stone you want to measure is not small enough to fit the refractometer, you can always leave the lid open. When you look through the eyepiece, you should keep a distance between 4 and 6 inches to be able to observe the scale clearly.

You will have to observe a blue-green flash line and to do that, you will need to move your head in whatever direction you like until you see it. Up, down, left, right, closer to the eyelid or further, it doesn’t matter. Keep trying until you spot the line. If the scale is dark all over, it means that the refractive index of the gem you are measuring it too high.

You would look at the top of the blue line and read the refractive index on the scale. That is your measurement. You can find a refractive index chart online if you may get it from the refractometer manufacturer and you have to compare your results to that chart. Now that you know how to use a refractometer for gems, you will be able to better enjoy your experience.



Ioana Moldovan

Ioana’s professional experience in the optics field has helped her understand the value of passing her knowledge forward. Her curious personality helps her gather useful information for her readers and her goal is to make technical information fun and accessible to everyone.

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