The Science of the Best Sorbet
The best sorbet I ever made was also the simplest. It was in 2013 during a glut of great strawberries, when 20 pounds of the fruit cost me all of $40 in Chinatown. I puréed 'em, added sugar, salt, and some lemon. That's it. After a few spins of the ice cream maker I had the creamiest, jammiest, and, well, strawberriest sorbet I've ever tasted.
Therein lies the golden rule of great sorbet: start with good fruit and don't screw it up.
But sometimes, despite your best intentions, good sorbet goes bad: it freezes too icy, or it tastes too sweet, or it melts into a puddle as soon as you start scooping. Though it's just as easy to make as ice cream, sorbet is a little less forgiving—its lack of fat and eggs mean you have to be more careful with your recipe.
Now the good news: sorbet has a science like anything else, and once you learn a few things you'll be ready to turn any fruit into fresh, full-flavored, and creamy sorbet—something so creamy you might confuse it for ice cream.
Sorbet in a Nutshell
Sorbet is usually made with fruit and is almost always dairy- and fat-free, but the strictest definition is simply a syrup of sugar and water that's churned in an ice cream machine. That's it: you could make a sorbet with nothing but plain water and sugar.
Sugar doesn't just sweeten sorbet—it's also responsible for sorbet's structure. In ice cream, a combination of fat, protein, and sugar all influence ice cream's texture, but in sorbet sugar is the big fish.
When you dissolve sugar in water you get a syrup with a lower freezing point than water alone, and the sweeter a syrup is (i.e. the higher the concentration of sugar), the lower the freezing point becomes. As water starts to freeze in a syrup, the unfrozen water becomes, in effect, a more concentrated syrup. This process continues until you have a bunch of small ice crystals in a sea of syrup so concentrated that it'll never really freeze.
Know Your Fruit
Remember the golden rule of sorbet? Use good fruit. No, scratch that—use the best fruit you can find: the most fragrant watermelon or the sweetest strawberries or the most ripe, juicy peaches. Nothing matters more to a sorbet's flavor than the fruit you start with.
Beyond that golden rule, the type of fruit, and what it brings to your sorbet, matters. Fruit high in pectin (berries, stone fruit, and grapes) or fiber (mangoes, pears, and bananas) are high in viscosity and full of body, and they make for an especially creamy sorbet that approximates the texture of ice cream. That's because pectin and fiber act as thickeners, their long starchy molecules working like sugar to physically get in the way of growing ice crystals.
By contrast, watermelon and pomegranate juices are thin with no body, so they need some special handling to make their textures as thick and creamy as berry or stone fruit sorbets. It's even trickier with citrus like lemon, lime, and grapefruit; not only does their juice lack pectin or fiber,* they're so tart they need extra sugar to balance their flavor, and even when you add enough, the resulting sorbet isn't as rich.
* Whole citrus fruit has plenty of pectin but it's all in the rind, not the juice or flesh.
Also pay attention to how much sugar your chosen fruit brings to a sorbet. Sweet strawberry purée needs less added sugar than tart lemon juice, and every batch of fruit varies in its exact sugar content depending on season, variety, and a dozen other factors we cooks can't control. But if sugar is our biggest trick for controlling a sorbet's texture, how do we sort through all the variables?
The pros have a handy tool called a refractometer, a small telescope-like device that measures the concentration of sugar in water. Refractometers can measure sugar concentration down to the percentage point (by weight), and once you know how sweet your starting fruit juice or purée is, you can start adding sugar until you hit your magic number, a sugar concentration between 20% and 30%.
You can buy a refractometer for about $30, and if you're willing to spend the cash, there's no better tool for nailing the precise optimal concentration of sugar in every sorbet you make, regardless of what ingredients go into it.
But can you make great sorbet without any extra special equipment? Sure thing.
The Master Ratio
Four cups fruit purée to one cup sugar. That's really all you need to know.
Okay, let's back up a bit.
If you don't know the exact sugar content of your fruit, the best thing you can do is play it safe. A sugar concentration between 20% to 30% will generally produce a scoopable, creamy sorbet.* Add less and your sorbet is too icy to scoop; add more and it may never freeze. But within that window you have some wiggle room, especially with high-pectin or -fiber fruit like berries and stone fruit, which add stability and richness to the sorbet.
* Of course there are exceptions to everything, so depending on the ice cream machine and other ingredients like stabilizers and type of fruit, these numbers may vary.
I start most of my sorbet bases at a sugar concentration of about 20%, then add the fruit's natural sugar on top of that. At most you tick up a few percentage points, but nothing to bring you out of the sorbet safe zone.
Two pounds of fruit, depending on the type, produces about a quart of sorbet. If you trim and purée that fruit, then pass it through a strainer to get rid of excess pulp and seeds, you'll wind up with about four cups of liquid. Add a cup of sugar to that purée (seven ounces by weight) and you wind up with a syrup that's 22% sugar, not counting the sugar already in the fruit.
But the ratio works: from strawberries to plums to even some thin juices like clementines, four cups of fruit to one cup of sugar makes a great sorbet that tastes like nothing but its namesake fruit: because it is nothing but its namesake fruit.
I've used this ratio for all kinds berries and stone fruit as well as pulpy fruit like mangoes and bananas—anything that has some viscosity and body once it's puréed. Since these fruits don't all weigh the same I actually prefer to go by volume—four cups of any thickened fruit purée will likely take well to a cup of sugar. For peaches, that may mean three pounds of fruit instead of two.
But don't confuse a master ratio with a master recipe—as you'll see in the recipes linked here, this is a ratio that may need adjusting. Since every fruit is different, every sorbet may need more or less sugar (less for super-sweet mangoes, for instance). Thicker fruits may need to be watered down while thin juices need bulking up with thickeners. You'll also have to add acid (lemon or lime juice are best) and salt to taste. This ratio is simply a starting point; use your own taste as your ultimate guide.
What About Simple Syrup?
Look at ten sorbet recipes and at least five of them will call for making a simple syrup of water and sugar, then mixing that syrup into fruit purée. I don't care for this approach for two reasons: it dilutes the sorbet's flavor by adding water and simple syrup is a nuisance to make. So why do so many recipes call for simple syrup?
For one reason, it's just how sorbet has been done for a long time, and old kitchen traditions die hard. Adding syrup to fruit purée is also a convenient way to streamline work in a busy restaurant kitchen—provided you have a big batch of simple syrup ready to go. But neither of these are particularly compelling reasons to dilute a sorbet base with water.
There's one rationale I can get behind: some fruits are just too thick when puréed on their own. If you don't add liquid to, say, puréed pears, you wind up with a sorbet that feels like frozen applesauce. That's why Harold McGee recommends diluting some fruit in his chapter on sorbet in The Curious Cook. I agree, but I'd rather swap out water for something more flavorful. In pears' case, Riesling is nice.
Make a few batches of sorbet and you'll get an instinct for what purées are too thick—they'll look more like slushies than melted sorbet. The solution? Thin out the purée with the liquid of your choice, then measure out four cups and proceed as normal.
Should I Cook My Fruit?
This is a personal choice, but I usually don't. On the plus side, cooking fruit concentrates flavor, drives off water for a creamier final texture, and allows you to infuse spices or herbs like ginger or mint. But when I make sorbet I want it to taste like nothing but fresh fruit at its absolute best. Cooking, no matter how delicately, kills that freshness.
Some fruit, like pears, cranberries, and some plums, tastes better when cooked. If that's the case, cook away, but no more than necessary to soften the fruit. When I do cook fruit for sorbet I add bright accents: herbs, citrus zest, spices, or ginger—otherwise the sorbet simply tastes...cooked.
Adding Body to Fruit Juice
The master ratio above works great with any fruit purée that has some body and viscosity. But what about thin juices like watermelon, pomegranate, and citrus? Without any fiber or pectin they tend to produce a thin and icy sorbet, even when made with the correct amount of sugar. What's more, they're less forgiving than berry or stone fruit sorbets, because there's nothing in them besides sugar to inhibit the growth of big ice crystals.
If you're dealing with citrus juice you have another problem: the juice is so tart it needs to be diluted and sweetened with care. Go ahead: try making lemon sorbet with four cups of lemon juice and one cup of sugar: you'll get something so lip-puckeringly sour you'll barely be able to choke it down.
The solution to both of these problems is an alternative kind of sugar, one with different sweetening and freezing properties than sucrose, a.k.a. table sugar.
Sucrose is fairly sweet and doesn't add much body to a syrup. That's why pastry chefs look to liquid sugar like invert sugar, glucose, or dextrose, which all make sorbet creamier when used properly. The easiest alternative sugar—the one you can find in any American supermarket—is plain 'ol non-high-fructose corn syrup. Trust me: it's lemon sorbet's best friend.
I've written a whole article on the benefits of corn syrup in sorbet, but here are the Cliff's Notes: 1) corn syrup is highly viscous, so it makes for richer, creamier sorbet; and 2) it's only one third as sweet as sugar, so you can use three times as much of it as sucrose—making your sorbet three times as creamy—without over-sweetening the end result. In a blind taste test, tasters almost universally preferred lemon sorbet made with corn syrup compared to sugar. You can see the difference in texture here.
Even small amounts of corn syrup (or other liquid sugars) can add body and creaminess to a sorbet made with sucrose. How much you use, and in what proportion to sucrose, will vary from fruit to fruit, but this lemon sorbet recipe is a good starting point for super-sour citrus.
Oh, and because I know you'll ask: no, honey, agave nectar, and maple syrup aren't good alternatives. For one, they bring strong flavors of their own that may or may not jive with your other ingredients. They're also not very effective; honey has more body than sucrose, but it's so sweet you can't use much of it; maple and agave don't have much body at all.
What About Alcohol?
Sorbet recipes often call for alcohol, sometimes as little as a tablespoon, to improve texture. Why? Alcohol reduces a sorbet base's freezing point, thus making the sorbet softer and easier to scoop. And the more alcohol you add, the softer the sorbet gets, until you add so much that the sorbet's freezing point is literally too cold to freeze in a conventional freezer (you start fiddling with this danger zone above five tablespoons of 80 proof alcohol per quart).
Alcohol certainly helps stubbornly icy sorbets become less icy, but it's not a miracle worker. Unlike sugar it adds zero creaminess of any kind—the sorbet will melt just as watery in your mouth. And alcohol-fortified sorbets are less stable, so they melt fast and have a tendency to re-freeze harder and icier than when they were first churned. If you're adding alcohol to a sorbet, do so in small increments, and don't leave your finished sorbet out of the freezer any longer than you have to.
Keeping it Fresh
Once you've spun your sorbet, how do you keep it in top condition? Keep it as cold as possible—in the back and bottom of your freezer piled with other items. Use an airtight container to protect your sorbet from funky freezer odors. And eat your sorbet fast—within a week for best results. Remember, this is fresh fruit we're dealing with. It doesn't last forever.
Want more storage tips? Head right this way.
And if it All Goes Wrong?
Sometimes sorbet just goes to hell. It happens to the best of us. It's okay. Really.
I've developed a few dozen sorbet recipes and every once in a while I screw up without knowing why. My sorbet will be freeze so hard I have to chisel it out of the freezer, or I added too much sugar and it froze into a sticky slush.
If you run into problems, don't throw away your hard work: just let it sit on a counter until it melts and fiddle with the recipe. Too sweet? Add more lemon, water, or fruit. Too icy? Add more sugar until you're satisfied. Underseasoned? Lots of sorbets are; simply add more salt and spin it again. Just chill your base down to 40°F or lower before you churn it again.
And if nothing seems to work and your sorbet is hopeless? Toss it in a blender with your choice of hooch and sip down that boozy slushy like the champion you are. Because sometimes dessert gives you a second chance.