America's Test Kitchen on the sweet science of syrup

Syrups can be used in recipes to sweeten and add body to everything from main dishes to desserts. But all syrups are not meant to be used interchangeably. Their different molecular structures mean some are better for certain uses.  To learn more about the science behind syrups Managing Producer Sally Swift talked with Dan Souza, Editor in Chief of Cook's Illustrated. One syrup they talk about is the British classic, Lyle's Golden Syrup. Use it specifically to make this wonderfully delicious America's Test Kitchen recipe for Frozen Yogurt.

Sally Swift: We recently spent a day talking with the wonderful Nigella Lawson. And while we didn't get a chance to talk to her about all those crazy English desserts like the flummery and the Eton mess, it got me thinking about that classic English syrup called Lyle's Golden Syrup. It comes in that beautiful green tin can and it has a toasty flavor. What do you know about it?

Dan Souza: It’s definitely a classic, and I love that’s got that mild caramelized flavor. It's not as in-you-face as maple syrup but it's nice. It shines best in a classic British dessert called a treacle tart, which is so popular it even shows up in the Harry Potter books – it’s kind of a cult favorite and I love it in that application. But I think Americans could get a lot out of Lyle’s if they search for it. Years ago, we found an awesome use for Lyle's Golden Syrup and that’s in frozen yogurt. That might sound kind of strange, but it's really cool. It gives us frozen yogurt that is easier to scoop right out of the freezer, it’s creamier and less icy; it doesn't have a lot of that harsh, rough ice that you feel on your tongue in some frozen yogurt.

Dan Souza Photo: America's Test Kitchen

The reason that Lyle’s is key to that is based on its composition. Lyle’s is considered 50 percent inverted. I'm going to get a little bit nerdy here to explain what that means. When we talk about a syrup where you just took regular white sugar and dissolved it in water, that would be sucrose, which is white table sugar. But if you do certain things to it – like heat it with an acid or add an enzyme to it – you can break that sucrose down into its building blocks. Every sucrose molecule is made up of one molecule of fructose and one molecule of glucose. With Lyle’s, 50 percent of the mix has been converted from sucrose into those smaller molecules of sugar. The reason that matters is when we talk about frozen desserts like ice cream and frozen yogurt we want to keep some of the liquid in that mixture liquid; we don't want it to all freeze. If it all froze you'd have an ice cube of ice cream that wouldn't be very pleasant. The more sugar molecules we pack into an ice cream base or a frozen yogurt base the more of that liquid will remain liquid in the freezer. So, by adding Lyle’s we're adding basically the same amount of sugar overall but more sugar molecules for every quarter-cup that we add. Those additional sugar molecules keep more of the water as a liquid, it will be easier to scoop, and taste a lot creamier.

SS: I didn't understand that about frozen things, that sugar affects the texture in frozen things. Will any syrup work when you are working with frozen sweets?

DS: They will all work a little bit differently, and it's really going to depend on their composition. We've also had good luck using corn syrup in ice cream recipes. That composition is a little bit different; it’s got a fair amount of glucose in it, but it also has these broken starch chains that give a ton of viscosity to corn syrup. When you pour corn syrup you can see that it's really thick, but it's not actually that sweet. It’s got these starch chains that kind of get in the way. That viscosity that adds thickness helps when you're making ice cream as well because it slows the movement of water molecules, so fewer of them bump into one another and form large ice crystals. We get a similar effect with corn syrup but for a slightly different reason.

America's Test Kitchen Recipe: Frozen Yogurt

SS: What about something like honey?

DS: Honey is interesting. It also has a fair amount of fructose and glucose. Those smaller sugars aren't just useful for ice cream making, they're also useful in browning. We talk about browning on baked goods and steaks and roasts; if you add honey into the mix as opposed to just using white sugar you can get deeper and more complex browning and better flavor.

We did this really cool test where we took one whole side of salmon, and on one-third of it we brushed on some honey, one-third we left plain, and on the final third we put a little bit of white sugar. Then we put under the broiler. The side with honey on it got absolutely gorgeous brown over the entire surface; it's because of those smaller sugars in there that promote caramelization and Maillard browning.

SS: That's so interesting. And all of this stemming from a thought about Lyle’s.