The science of slushy drinks and how to make a good one

What’s cooler than being cool?
What’s cooler than being cool?
Image: Daniel Wolfe
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Trying to make a Starbucks-style Frappuccino at home? Or even just trying recreate the texture of that smooth flavorful slush? The secret to the drink that drives 11% of the coffee company’s US revenue is xanthan gum.

What is xanthan gum?

Xanthan gum is a carbohydrate that’s produced when bacteria called Xanthomonas campestris eats. Allene Jeanes a chemist at the US Department of Agriculture, honed the process of deriving it in the 1940s. These days, it comes in a powdered form for commercial and home kitchen use.

Besides Frappuccinos, xanthan gum has been used to create bread-like chewiness in gluten-free baked goods, freezer-burn resilient ice cream, unseparating salad dressing, and easily squeezable toothpaste.

In the US, xanthan gum can be easily found online and in stores. It’s sold by brands like Red Mill in the US, and Doves Farm in the UK.

Why does the gum make for better slushy drinks?

If you’ve ever made a fruit smoothie with ice cubes, you might have noticed that the drink tends to separate. A layer of fruit bits is suspended in the ice and a thin liquid sinks to the bottom. That’s because the sugars in fruit promote the formation of ice crystals in water molecules. Xanthan gum inhibits the creation of ice crystals.

The gum is promoting a gel-like structure to form. That’s because it’s a hydrocolloid: an insoluble molecule that is attracted to water. Water molecules are suspended in the gum, preventing them from forming a tight icy bond together. The result is a mouth feel that’s smooth and viscous versus brittle and coarse.

It also keeps our booze well mixed.

A photo of a hand holding up a glass of the finished cocktail: frosé. The scene is a backyard at sunset.
Sunset slurry
Image: Daniel Wolfe

How do I pour one out?

As a party drink, frosé is exceptional. I was bold enough to serve them at a Quartz staff party this summer. The drink stood up well to our pulled pork taco bar, and butter miso grilled corn.

I’d argue it performs best in this kind of environment. The watermelon dilutes the alcohol level to between 4% and 6% depending on the wine, ensuring you can sip these at any pace. The herbaceous back notes from the elderflower keep your company guessing at the hard-to-place finish.

I raise my glass to Smitten Kitchen, for the inspiration to blend frozen watermelon, which protects the flavor profile sweet and undiluted.

Is xanthan gum safe?

“Food additives” are often perceived as unnatural or suspect. Xanthan gum is neither. It is a safe to eat according to the US Food and Drug Administration and the result of a natural plant-based fermentation process.

The vegetable gum’s popularity and versatility also means it’s nearly impossible to avoid in your diet. From ranch dressing, ice cream, to gluten free pizza, and now…frosé.