Early drafts of the fruit theory posts have been slow going—and people have been bugging me for something they can use. So here’s a sample sorbet recipe, developed with strawberries, but which also works well with peaches (they have similar solids and sugars levels).
This will be the best sorbet you’ve ever had, if you use good fruit. I’m quite confident of this, because every sorbet I’ve encountered, whether at artisanal ice cream shops, grocery stores, or high-end restaurants, has suffered from similar flaws. They’re always at least a little icy. Even when they border on smooth, they have a short texture that’s miles from creamy. And they’re all horrifically too sweet.
These problems result from the technical challenges inherent to sorbet: there’s no milk protein or lactose controlling the water, there are inadequate sources of solids, and the only way anyone’s figured out to get the freezing point depression to the right place and to create any body is to pile on the sugars. Sorbet is typically 20 to 30% sugar, with POD (sweetness) values well over 200. This is insane. I don’t want this in my mouth. The gods made fruit with 4% to 13% sugar. It doesn’t improve by turning it into candy.
There are some other reasons for these problems, stemming from old habits. Most professional recipes have two parts, like an epoxy: a sugar syrup and a fruit puree. This allows a generic syrup to be kept on hand to combine in varying proportions with different fruits. It also allows easy dissolving of the sugars, and easy hydration of any stabilizers. This approach is convenient, but there’s a price: it forces you to add substantial quantities of water. Most fruit is already around 90% water. We’re not looking for more! So we have found a way out of the syrup trap.
Our Approach: 75% Fruit, 25% Science
Most professional sorbet recipes use around 40% fruit by weight. We come close to doubling this, because the whole point is the fruit. The remaining 25% of ingredients have to work very hard, in order to provide adequate freezing point depression, ice crystal depression, and texture control—and do it all without sending sweetness levels through the roof. There may be some unfamiliar ingredients here. We’ll discuss them below.
Strawberry Sorbet Formula
750g Strawberry (brix 8-9)
65g Atomized Glucose DE40
2g Carboxymethyl Cellulose
1g Lambda Carrageenan
-Hull strawberries and remove any brown or soft spots. Weigh afterwards
-combine dry ingredients
-blend water and strawberries until pureed. Turn down speed until it’s just fast enough to make a vortex.
-Add dry ingredients. Blend for a full 2 minutes. Use a high-powered blender on top speed, to make a perfect puree that doesn’t need straining.
-Check to see that all sugar is dissolved. Blend more if if mixture isn’t perfectly smooth.
-Age in fridge for 2 to 4 hours.
-Spin in an ice cream machine. Ideal drawing temperature is -5°C to -7°C.
-Let harden in freezer at least 4 hours before serving.
-Ideal serving temperature is -12°C to -14°C
Total Fat: 0%
Total Solids: 24.7%
POD: 144 / 1000g (sweetness = to 14% sucrose)
PAC: 318 / 1000g
Absolute PAC: 438 / 1000g (freezing point depression = to a 44% solution of sucrose in water)
Ice Fraction @ -14°C: 74%
What’s going on here?
It’s not as arcane as it looks. There’s a lot of strawberries, a bit of water to help balance the formula, a cocktail of sugars, a cocktail of stabilizers, a tiny quantity of salt, and inulin (a vegetable fiber that modifies texture).
The sugars: the goal here is to get adequate freezing point depression and adequate solids, while keeping the sweetness down. This is why there’s no table sugar; it’s too sweet (although some is naturally present in all those strawberries). We rely on dextrose (low on sweetness, high on freezing point depression), dried glucose syrup (very low sweetness, high solids), trehalose (low sweetness, very high freezing point depression; very similar to the lactose in milk solids), and erythritol (a sugar alcohol that’s almost non-caloric, with low sweetness and high freezing point depression).
There’s a bit more to know about the sugar combinations. Trehalose, like dextrose, has strong water controlling properties and helps with texture. But it has low solubility, and can crystalize if you use too much. So we keep the level at 4%. Erythritol can produce a cooling sensation in the mouth (like mint) that’s a bit disconcerting. And in large quantities it can cause stomach rumbling. We keep it at around 2%. At this level there are no gastric effects, and it’s balanced by the inulin, which produces a warming sensation.
The stabilizers: this is similar to our usual ice cream blend, but we’ve replaced locust bean gum with sodium carboxymethyl cellulose (also known as cellulose gum). Unlike Locust bean gum, CMC hydrates cold. It lets us get away with not cooking the mix. This is critical for great sorbet; it saves us from having to make a separate syrup to hydrate the solids (which adds too much water) or from cooking the fruit (which kills it). CMC is also extraordinarily potent at suppressing ice crystals. It’s not especially popular, because it sounds like something you’d be injected with for chemotherapy. But we’re trusting that you’re smart enough to not judge an ingredient by the number of syllables. CMC is the best sorbet stabilizing ingredient ever discovered, and in real life is about as scary as the fiber in an apple peel. The other two ingredients are more familiar, but no less effective: Guar adds body and elasticity, while magnifying the effects of the CMC; Lambda Carrageenan adds creaminess to the melted texture. These both likewise hydrate cold.
Inulin: this vegetable fiber (extracted from chicory root) works a little like a sugar, a little like a fat, and a little like a stabilizer. It’s become something of a fad health food ingredient, because it’s an effective pre-biotic and constipation remedy, and has been shown to lower people’s blood triglyceride levels (very little of what’s on this blog will do anything good for your triglyceride levels, so this is a bit of a black sheep). It’s a darling among Italian pastry chefs, who use it to increase creaminess in typically low-fat gelatos; they’re the pioneers of artisanal inulin use. Previously Inulin was used most often in industrial low-fat ice cream. We use it for the same reasons as the factories and the gelatistas, although instead of it using at 6–7%, as you see in industrial ice cream, we aim for 4–4.5%. This isn’t enough to mimic a high-fat ice cream, but enough create the smoothness and luxurious melt that’s always been missing from sorbets. You can use more or less depending on your tastes.
Strawberries: Oh yeah—the strawberries! If you’re lucky, you can get good local ones that are a heritage breed, bred more for flavor than durability. But even modern, intrepid strawberries can be good when they’re at peak season, picked when mature, and well-ripened. Here in NYC, we get good strawberries about 3 weeks out of the year. The rest of the summer it’s at best a crapshoot. The above formula was built around halfway-decent strawberries, not great ones, because this is the best most of us can get most of the time.
How do you tell the difference? The old fashioned way is to taste them. Good ones will be very sweet, and have a complex, almost three-dimensional flavor with herbal overtones and a nice background acidity of citric and malic acids. When they’re less good, the sweetness and fresh berry flavors are muted, the acidity dominates, and there may be a significant bitter aftertaste. Most of the best berries at farmer’s markets and specialty shops fall somewhere between these extremes. As long you’re getting good berry flavor, and as long as the bitter aftertaste stays in the background, you can work with them. If not, pick a different project.
The higher-tech, repeatable way is with a brix refractometer. This is an optical device that measures the total dissolved solids in any liquid, as long as those solids have a refractive index similar to that of sucrose. With fruit, most of the dissolved solids are sugars. Because the average refractive index of those sugars is usually pretty close to that of sucrose, and because sugar level tracks closely with ripeness and quality, brix is a pretty good quality indicator.
One source (David Pelly at BEDA Biologics) gives the following guidance for strawberry brix values:
I suspect these values are a bit optimistic; I’ve never encountered strawberries that measure even 14. A brix of 10 correlates with pretty damn good flavor. Another source, the USDA’s Nutritionist V. Database, says the average brix of strawberry is 6.9, based on the following breakdown:
Total sugars: 7%
Total solids: 10%
POD (sweetness relative to pure sucrose): 8.8%
PAC (freezing point depression relative to pure sucrose): 11.9%
Other Strawberry Details: They’re very low in pectin, so they don’t contribute anything that helps with stabilization (besides sugars). They’re pretty acidic, at 0.85% titratable acidity on average. In a formula that’s 75% berries, there’s no need for added lemon juice or any other source of tang.
How to use Brix
It’s not uncommon to see pastry chefs at the fruit market taking samples, crushing pieces with special pliers, and holding their instruments up to the sky to see if the sample is worthy. As someone who’d rather not completely alienate the farmers, I’m more likely to just taste a sample and make sure it’s subjectively good enough. Then back in the kitchen I’ll pull out the refractometer. The idea is to compare the measured brix value to whatever average brix value you’ve based your formula on.
I use the Nutritionist V. Database, which assumes an average brix of 6.9.
If I measure 8.5, then this is 1.23 times the average. Use this as your conversion factor.
Multiply the total solids, the POD (sweetness) and the PAC (freezing point depression) by this factor.
|Average Value||Multipled by 1.23 conversion factor|
Where do you get all this data on fruit? How do you apply the math to balancing a formula? We’ll be writing more about this in upcoming posts.
Is all this scientific geekery necessary for making great sorbet or ice cream? No. But it will be helpful if you’re aiming for precise and repeatable results, or if you’re working through iterations trying to perfect a formula. If you’d rather keep it simple, you can take advantage of our geekery by staying close to our formula … then just make sure you use fruit that tastes good. You’ll do fine.