Designing Sorbetto

The frozen dessert without milk

Sorbetto is an old frozen dessert — one could call it the original form of today's gelato. Its base composition is water, sugar, and fruit (juice or pulp), and nothing more. No milk is used, so the solids consist, in essence, of sugar alone.

For design, this means a great deal. Sorbetto has none of the fat and milk solids of Chapter 3 — the components that give corpo, build the frame, and help the melt. Of the four phases Chapter 1 laid out, the structure must stand with the fat globules missing: on sugar, stabilizers, and air alone. That is why the design of the sugar decides everything. Sorbetto is the frozen dessert in which the sugar theory of Chapter 2 is tested in its purest form.

One neighbor is a different thing altogether: granita. Stirred hardly at all, it keeps coarse crystals of ice, and its sugar stays low — about 17–21 °Bx in solution. The smooth-frozen sorbetto aims at another texture entirely.

Measuring the fruit's sugar with a refractometer

The design of sorbetto comes down to one act: measuring the sugar exactly. Yet the sugar of fruit swings widely with variety, origin, and ripeness. The same strawberry brings different sugar at peak ripeness and picked early. Guesswork is not design.

To put a fruit into a formulation is to reduce a thing like this to a single number. There is flesh, there is a stone, there is skin, and ripeness moves what is inside. What the refractometer reads is only the sugar.

Indispensable here is the refractometer (rifrattometro). It reads the soluble solids of a solution at once, as degrees Brix — roughly, the weight percent of sugar. The hydrometer (the Baumé scale) loses accuracy because the mix holds sugars of different molecular weights, the more so once stabilizers enter. So for sorbetto and gelato, where the split of the sugars is being built, the refractometer is the standard. But the Baumé scale is not useless. For a granita mix, where the sugar is nearly all sucrose, the literature holds it sufficient to this day. Measure the fruit's sugar in Brix, add the sugar of the base syrup, and land on the target total. This is the basic movement of sorbetto design.

In practice, a base syrup with the stabilizers dissolved in it is commonly made ahead. The usual strength is 55 °Bx (55 percent sugar). It is pasteurized, sealed and refrigerated, and — because it carries stabilizers — used up within 5 to 6 days.

The target ranges

The sugar of a sorbetto lands, by kind, in roughly the following ranges. Sugar is nearly the only solid, so these values are, almost as they stand, the total solids.

These 27–33 deserve one reading side by side with the table of Chapter 5. There, the total solids of the sorbetto family stood in a band of roughly 28–32 percent. In sorbetto, sugar is nearly the only solid — so total sugar in Brix and total solids are the same thing on two scales. The two bands should overlap, then. Yet the edges differ — and that is not a contradiction. First the upper edge. Load the sugar to 33, and the total solids pass the top of the band. But recall Chapter 5: the three ceilings of the sugar split could not be used at once. The edges of a frame are not values to reach for together. What bites on falling outside is the consequence on the total-solids side. Too low, hard and cold; too high, soft and at times powdery (Chapter 5). Then the lower edge. That this chapter's 27 sits below the band is because the Japanese widening is designed as a pair. Hold the sugar down, and at the same temperature more of the water freezes. So Japanese practice sets the serving temperature warmer as well (Chapter 8). What steps below the band, the serving side receives.

Where a sorbetto carries alcohol, the sugar is held low because alcohol itself depresses the freezing point strongly. Let the two depressions stack, and the sorbetto will not set — so the sugar side gives way. The PAC thinking of Chapter 2 is at work here too.

One distinction is worth drawing before going further. "The alcohol sorbetto" is not one kind.

A sorbetto of wine or spumante stands on its own — a light, cooling plate, welcome in the middle of a meal. But a sorbetto built on liqueur alone is rejected outright by the literature. To balance water, sugar, and alcohol rationally, it says, is like trying to square the circle. The form was once a fashion in France, and there is a reason, so the verdict goes, that it has not come back.

How, then, to use a liqueur? Add a little of it to a fruit sorbetto. Used this way, the aroma rises and the taste grows fuller. Three working points:

• Add it at the end of mantecazione. The earlier it enters, the further the freezing recedes.
• Keep it within 3 percent, counted as pure alcohol. Past that, the freezing-point depression becomes a burden on the structure.
• Choose the partner from the fruit's side. A sharp fruit takes a clean spirit; an aromatic fruit is answered with aroma.

Approfondimento — deep diveDesigning pairings — joining ingredients by aroma↓ Go deeper

Choosing the sugars — what changes in sorbetto

In sorbetto, the use of the sugars shifts a little from the milk-based gelato.

• To hold sweetness down, use glucose syrup. The guide is up to 15 percent of the total sugars, counted as solids.
• Dextrose and invert sugar are avoided in a fruit sorbetto bound for the display case. Their freezing-point depression is too strong. The fruit already brings in monosaccharides (fructose), and the freezing point falls until the storage and selling temperatures must fall with it.

There is a reason these two are written as guides. The literature recommends both — and then, in the worked examples later in the same chapter, follows neither. In its low-sugar sorbetti with alcohol it uses dextrose and invert sugar without ceremony, and its glucose syrup passes 15 percent. This is not a contradiction; the aim is different. Those examples are plates to be eaten on the spot — annotated, by the literature itself, as extremely fragile. Where no shape must hold in a case, there is no reason to fear a sugar that lowers the freezing point.

A rule of avoidance is tied to its purpose. If holding shape in the display case is required, the two rules above bite. If it is not, they may be set aside. Decide first which side you stand on.

The 15 percent here is a ratio of solids to solids, water excluded. The table of Chapter 2 was built per gram of the material as weighed from the bag — a different denominator. With the dried form of glucose syrup (solids near 100 percent), the two nearly coincide. With the liquid form (about 80 percent), they do not — landing on 15 percent at the scale has not measured this ceiling. And the "up to 20 percent of the sucrose" of Chapter 5 is the general guide, milk-based gelato included. In sorbetto, this 15 percent binds first.

Chapter 5 warned that the flesh of the fruit brings its own monosaccharides. Sorbetto is the frozen dessert where that constraint stands furthest forward. Grasp the fruit's sugar in Brix, and design down to the kinds of sugar added.

Acid last, and by taste

A fruit sorbetto — above all an acid one — is tightened with an acidifier: lemon juice, citric acid. Two iron rules here.

First, the amount cannot be set by number. Every fruit has its own pH, and the target acidity is a judgment of the tongue. Second, and most important: acid goes in last, just before mantecazione. Enter it early, and the mix destabilizes. Recall the acid coagulation of casein (Chapter 3) and the acid-weak stabilizers (Chapter 4), and the reason is plain. No milk is used; the constraint of pH reaches sorbetto all the same.

Fragile, so serve it fresh

The structure of sorbetto, without fat or milk solids behind it, is fragile. It does not keep, and this is why it is not mass-produced industrially. Served within hours at the table, the next day at the longest, it shows its true worth: light, full of juice, made to quench.

Chapter 10, next, turns to the ingredients with habits of their own — chocolate, nuts, alcohol — and how to design around them.