Use Brix for the Perfect Slushie Mix
Science is present in every kitchen and foodservice operation, whether you're searing steaks or checking temperatures for HACCP protocols, but the amount of science and number of measurements that go into developing slushie recipes may surprise you. While pre-mixes are available, if you want to develop your own recipes to use in frozen drink machines, you're going to have to learn about Brix and how to use a refractometer.
A Foundation of Brix
Brix is a measurement you will need to use to create any frozen drink mix, as it will determine the consistency at which the drink freezes and affect the quality of the product you serve. A drink mix with the proper Brix measurement won't freeze solid and damage your frozen drink machine. Brix is a unit of measurement for the sugar content of a liquid solution, with 1 degree Brix equaling 1 gram of sugar in 100 grams of water. Brix is measured with a refractometer, which uses how light refracts through the liquid to determine the volume of dissolved solids, like sugar, within it.
Generally, water freezes at 32 degrees Fahrenheit, forming ice crystals that eventually solidify into ice. Sugar particles suspended in the water make that freezing process more difficult by physically hindering those ice crystals from bonding with each other. When there is more sugar present in the mix, the formation of ice in the liquid is inhibited, which means it must be colder before it will freeze. This is especially true in a frozen drink machine that keeps the mixture moving. Not checking the Brix measurements on your slushie mixes can lead to a solid block of ice and a burned-out slushie machine. On the flip side, a Brix measurement that's too high will prevent your drink from freezing into the slushy texture that customers crave.
Using a Refractometer
If you've ever looked at a straw in a glass of water, you've probably noticed how it looks like it bends as it meets the liquid. This effect is caused by refraction, or light bending as it moves through different mediums, whether those mediums are solids, liquids, or gases. Because light moves differently through water than air, it gives the straw a bent appearance. Refractometers use prisms to measure how light moves through the liquids you test to determine how much sugar is dissolved in the mix.
To use a refractometer, first follow the manufacturer's instructions to ensure it is properly calibrated. Add some of your liquid to the prism, close the light plate, and look through the viewing lens. The line between the differently colored sections is your Brix reading. Some sources say that frozen drink machines can function with a rating as low as 11 or as high as 18 degrees Brix (represented as °Bx), but most seem to put the target between 13 and 15 degrees Brix.1 While any liquid with this Brix measurement should work well in a frozen drink machine, it's always wise to keep an eye on it when you use it in the machine the first time, as any mistakes in measuring could lead to the mixture freezing solid. In 2002, 7-11 encountered some issues with this when they wanted to market slushies made out of diet sodas, which do not contain any sugar. While they finally figured out a way to make it work, during development the trial mixes often froze solid, destroying the frozen drink machines they were working with.2
There are many flavors of slushie syrup available, each with specific instructions that ensure the final mix has the proper Brix measurement. These syrups are a great way for beginners to get started with a slushie program, but if you want to offer unique flavors you will need to branch out with flavored extracts or syrups. If you've developed your own slushie mix and the Brix isn't quite where it needs to be, adjusting the mix is simple. To lower the degrees Brix of your concoction, simply add some water, mix, and measure again until you reach the desired reading. To raise the Brix of your mixture, add simple syrup, which you can order premade or make yourself with just some water and sugar.3. Always make sure to mix the solution thoroughly before taking a new reading.