A soft, scoopable texture
When I set out to make frozen yogurt for the first time, I thought the task would be simple. Unlike ice cream recipes, which typically call for cooking (and then cooling) a finicky custard for a base, most of the fro yo recipes I came across required nothing more than throwing yogurt, sugar, and maybe a few flavorings into an ice cream maker and churning. But these recipes were hugely disappointing: The fro yo turned out icy and rock-hard. I realized that this was partly because frozen yogurt doesn’t have the advantage of yolks or cream, both of which give ice cream proportionally more fat and less water. Fat makes ice cream taste creamier and smoother, while less water in the base means there’s less of it to form ice crystals, leading to a more velvety, scoopable texture. I found a few frozen yogurt recipes that tried to improve texture by adding cream to the mix. But while these versions did turn out less icy, their tangy yogurt flavor had been muted.
For me, this was a nonstarter. I wanted my frozen yogurt to put the fresh-tasting tartness of yogurt front and center. The challenge was to figure out how to do that and achieve a dense, creamy-smooth texture at the same time.
Strain and Drain
The obvious thing was to try to eliminate some water from the yogurt. In my initial tests, I had been using regular whole-milk yogurt (plain was a must, since I wanted to be able to control flavorings and sweetness myself). What if I switched to Greek yogurt, which has had much of the liquid whey strained out? When my first test produced an oddly crumbly texture, I switched to another brand and then another—but they all produced unappealing results.
For Creamier Fro Yo, Forgo Greek Yogurt
Making creamy, smooth frozen yogurt is largely about limiting water, since less water translates to fewer large ice crystals. Thus we were surprised when frozen yogurt made with Greek-style yogurt, which has been strained of excess liquid, churned up crumbly and chalky. The reason for these results is twofold: First, Greek-style yogurt has a particularly high protein content (in lab tests, we found that it had almost twice as much protein as regular yogurt we strained ourselves). Second, it’s often strained by centrifuge, which can damage these proteins and increase the likelihood of a chalky texture. So while it may seem like a timesaver to reach for Greek when making frozen yogurt, you’ll pay for that convenience in texture. That’s why we take the time to strain regular yogurt for the creamiest, smoothest results.
So I considered another option: straining regular yogurt. I spooned a quart of yogurt into a fine-mesh strainer lined with cheesecloth and set over a bowl and left it overnight. By the following morning, a generous amount of whey had drained into the bowl. The fro yo I made with this yogurt was much smoother; I knew this step was a must.
Inverting the Problem
The next ingredient to go under my microscope was sugar. Just as in ice cream (and sorbet for that matter), sugar doesn’t serve as a mere sweetener in frozen yogurt. It also affects the texture. Once dissolved, sugar depresses the freezing point of water, which means the more you use, the more water in the mix will stay in liquid form after churning. That translates not only to fewer ice crystals but also to a softer, more scoopable product straight from the freezer. But balance would be key—I didn’t want to make it so sweet that the yogurt’s flavor was overshadowed. I found that I could go up to a full cup of sugar per quart before the yogurt turned too sweet.
I also knew from my ice cream testing that there were other sweeteners worth considering beyond the granulated stuff. One secret to the velvety texture of an ice cream recipe I’d developed a few years back was swapping out some of the granulated sugar for corn syrup. This sweetener contains starch chains that keep water molecules from joining up and forming large ice crystals. When I tried it in my frozen yogurt, it worked pretty well at minimizing iciness, but the yogurt’s flavor seemed muted. A little research informed me why: Those starch chains trap flavor molecules. This wasn’t a problem in tame vanilla ice cream, but in tart frozen yogurt, the dulling effect was clear.
My next thought was to try incorporating a source of invert sugar, which is better than granulated sugar at depressing the freezing point of water. Why? Unlike granulated sugar, which is made up of larger sucrose molecules, invert sugar is made up of two smaller molecules, glucose and fructose. Freezing-point depression is directly related to the number of molecules dissolved in the water. So a tablespoon of invert sugar provides twice as many sugar molecules and roughly twice as much freezing-point depression as a tablespoon of granulated sugar. Supermarket options for invert sugar include honey and agave syrup, but each has a distinct flavor that I didn’t want in my frozen yogurt. Luckily, I knew of another option: Lyle’s Golden Syrup. While only half invert sugar (the other half is sucrose), Lyle’s was good enough to work magic. Just 3 tablespoons (along with ¾ cup of granulated sugar) noticeably reduced the iciness. This was impressively creamy frozen yogurt. But I suspected I could do better.
Many manufacturers add pectin, gums, or modified starches to get smoother, less icy results. These ingredients essentially trap water, which will minimize large water droplets—and thus large ice crystal formation. Pectin and gelatin seemed most promising, but the citric acid in pectin made the frozen yogurt taste almost fruity. Gelatin, however, was perfect. I needed a liquid to bloom it in, so I reserved ½ cup of whey when I drained the yogurt and microwaved the whey with the gelatin to quickly dissolve the gelatin before incorporating the mixture into my base. Just 1 teaspoon of gelatin gave me the smoothest, creamiest frozen yogurt yet.
There were just a few more details to attend to. Quickly freezing the base was key, since faster freezing, along with agitation, promotes the formation of smaller ice crystals. I refrigerated my base until it registered 40 degrees or less before churning. And as with my ice cream recipe, in addition to churning until it looked like “thick soft-serve,” I also made sure it registered 21 degrees (the temperature at which roughly 50 percent of the water has frozen) for the most consistent results.
My frozen yogurt took some time, but it was mostly hands-off. And best of all, it boasted a wonderfully creamy, smooth texture as well as the distinctively tangy, fresh flavor of its namesake ingredient.
Keys to Success
Minimal icinessFirst, we strain regular yogurt before churning to remove excess liquid that would increase the number of large ice crystals. Second, we add gelatin, which traps some of the water molecules so they can’t join together to form large ice crystals.
A soft, scoopable textureWe substitute an alternative sweetener, Lyle’s Golden Syrup, for some of the granulated sugar because it contains some “small sugars”—glucose and fructose—that are better at lowering the freezing point of the base. A more depressed freezing point means more of the water in our frozen yogurt base stays in liquid form once churned—and that makes it softer and easier to scoop straight from the freezer.
Tart flavorWe use only yogurt for the dairy component, no cream or milk.