[This article was substantially revised in April 2019 and June 2019. Thanks to experience and advances in our software analytics, we’ve updated our approaches to sugars since this first went live in 2016.]
Sugars: they’re sweet, and they keep the ice cream soft. If you’ve had homemade ice cream with the consistency of concrete, it’s because the level of solids—especially sugars—was too low.
Some bloggers and cookbook authors tell you to soften the ice cream by adding alcohol. This works, but you can do better. While alcohol depresses the freezing point, it does so at the expense of smoothness. By increasing the unfrozen portion of water in the ice cream, while doing nothing to help control that water, it will encourage ice crystals to grow larger. You’ll end up with a softer but grainier texture.
Dextrose (another name for the monosaccharide d-glucose) is about 3/4 as sweet as sucrose, but has nearly double the effect on freezing point suppression. Simply by decreasing sucrose and increasing dextrose, you can lower the sweetness while simultaneously softening the texture. Magic! Dextrose is also hygroscopic, meaning that it holds onto water, reducing the formation of both ice crystals and sugar crystals. It’s effectively a stabilizer, although it’s much less powerful than dedicated stabilizers.
Dextrose, fructose, and invert syrup can be especially helpful with flavors that require adding non-dairy fats, like cocoa butter (chocolate) and nut oils (nut butters). These fats tend to freeze harder milk fat, and give ice cream a dry, stiff, crumbly texture. Increasing the proportion of these monosaccharides can help preserve a smooth texture.
Other Important Structural Sugars
Atomized Glucose is useful in odd cases when you need maximum solids, high freezing point depression and minimum sweetness. It contains dextrose, and a whole stew of other mono-, di-, and polysaccharides, including dextrins. This gives it bulk without much sweetness. The trouble with atomized glucose is that it’s not a consistently defined product; you don’t know for sure what you’re getting or what its properties will be. Atomized glucose is a pantry staple for some pastry chefs, especially in Europe. It leads to some confusion, since some chefs don’t know the difference between it and dextrose, and some recipes don’t specify which to use.
Maltodexrin adds solids and bulk with minimal effect on sweetness or freezing point. It’s a bit of an anti-sugar in this sense. It’s useful in particular sorbet flavors which by their nature are low on solids, and so need something to combat their innate wateriness—ones like lemon and watermelon. These flavors are built from fruit juices that are mostly water. Maltodextrin is a bit like atomized glucose minus the glucose. We’ll address sorbets generally in another post.
In ice cream, skim milk powder works better than maltodextrin. And the latter does all the bad things to your body that sugar does, without the benefit of tasting like anything. But milk solids are generally not an option in sorbets, which everyone expects to be dairy-free.
Inulin is technically a starch (derived from plants like chicory and Jerusalem artichokes), but we’re including it here because it offers some sugar-like behavior (some sweetness, some freezing point depression). It’s mostly used as a non-caloric fat replacer, since it has textural qualities similar to fats (this use is outside our purview; if you’re on some kind of diet, you’ve walked into the wrong room). It is, however, pure magic in sorbets, used at around 3.5% the water weight of the formula. It’s slightly exothermic, so it produces a mild warming effect when it melts in your mouth. This can counter the (usually undesirable) cooling effect of ingredients like erythritol. Inulin is interesting to us for cases where we need high solids without a lot of sweetness or freezing point depression. Nominally it doesn’t look as good as maltodextrin for this purpose, but inulin’s textural properties allow it to behave like a much larger dose of solids. You can think of it almost as a specialty stabilizer that also adds POD and PAC. As a bonus, it doesn’t have the lousy health impact of maltodextrin, and is non-dairy—which makes it an ideal choice for adding bulk and creaminess to sorbets.
Trehalose is a naturally occurring disaccharide composed of two glucose molecules stuck together. It’s much less sweet than sucrose, but has the same freezing point depression factor. Its properties are very close to those of lactose. But since the source of lactose is milk solids, it’s not useful in sorbets. Sorbets are the ideal application for trehalose, where it’s often a battle for getting the solids and freezing point correct without creating a cloying sugar-bomb. Trehalose does have a some disadvantages compared with lactose. It’s much less soluble, so we usually limit quantities to a few percent. Relatedly, it does not offer the incredible water control of lactose. It’s also an uncommon ingredient, in many cases leading us to special orders and jacked-up prices, so it’s good that we don’t need piles of it.
Erythritol is a naturally occurring sugar alcohol that provides sweetness with virtually no caloric value. We mammals don’t have the enzymes needed to break it down. Many sugar alcohols are, however, highly digestible to our gut bacteria, which can lead to gas and bloating. Erythritol is much less problematic in this regard. It’s primary drawback is its high price. It’s also endothermic, meaning that it that pulls in heat as it dissolves, creating a cooling effect in the mouth. This is refreshing in breath mints, but not so pleasing in an already-cold dessert. This can be combated with an exothermic ingredient (like inulin) or by just limiting the amount you use. The key benefit of erythritol is its very high PAC:POD ratio, making useful for controlling freezing point and sweetness in sorbets.
Lactose is the sugar that’s already in your milk and cream. Skim milk powder is about 50% lactose by weight—so you might as well just get your lactose from the SMP, which belongs in every recipe anyway. Lactose has the same freezing point depression factor as sucrose, but with sweetness that’s so low it’s barely detectable: highly useful for increasing solids and freezing point depression independently of sweetness. Lactose is also a champion in terms of water control. Lactose can absorb roughly six times its weight in water, which gives some stabilization power, and makes it more effective than most other sources of solids.
[These guidelines differ somewhat from the formulas you’ll see elswhere in the blog series. We will eventually update those formulas to reflect this more refined approach]
How to Tweak:
Is the consistency ok but the sweetness too high? Less sucrose, more dextrose. Maintain PAC and decrease POD
Are you adding flavor ingredients that have their own sugars? Like fruit, chocolate, gianduja, or liqueur? Calculate (or estimate) the amount of added sugar and reduce the sucrose by the same amount.
With fruit, look up the actual composition of the fruit (it usually contains sucrose, fructose, glucose, and other sugars). You can compensate by reducing the glucose as well. We’ll discuss this in detail in a future post on fruit flavors. Or, as a shortcut, use calculated POD and PAC values for each fruit, and adjust the sugars to compensate.
Honey is a useful sugar in some ice cream flavors. It behaves mostly like invert syrup (because it IS mostly invert syrup—around 75% by weight), and tastes rather strongly … of honey. Because it adds about 20% water to the recipe, and increases body, it’s generally not a good idea to substitute honey for all the sucrose. But up to 50% works fine. It can be interesting to experiment with some of the more exotic and intense honey varieties, like buckwheat, heather, and chestnut. You’ll probably want to use these honeys in moderation. Mild honeys like clover and alfalfa are most traditional.
There are other varieties of glucose, including atomized glucose powder, corn syrups (typically around 1/3 glucose by weight) and various glucose syrups, identified by their DE number for dextrose equivalence. The DE number technically refers to the percentage of reducing sugars—in this case meaning either glucose or fructose. The higher the DE number of a glucose syrup, the more glucose it likely contains, and the greater the freezing point suppression. Atomized glucose is just spray-dried glucose syrup. It contains more water than anhydrous dextrose. Here’s all you need to know: Don’t use any of this stuff unless it’s all you can get your hands on. Pure Dextrose powder and invert syrup are more useful, and make it a lot easier to know what you’re getting.
Caramel is useful as a flavor ingredient. A little goes a long way, which is convenient—because it’s hard to know how caramel will effect the ice cream’s texture and freezing point. Caramelizing sugar is a gradual process by which some portion of the sucrose molecules break down into smaller molecules, and combine into larger, more complex, more flavorful ones. I like to use a small quantity of caramel, but to cook it to a fairly dark and flavorful degree. This way it will behave less like sugar in the recipe, and will have maximum effect on flavor.
You might also experiment with using caramels browned to different degrees—like a medium caramel, for more traditional toasted flavors, and a dark caramel, for the more complex and bitter burnt sugar flavors.
Caramel is challenging to calculate for. Its sweetness diminishes gradually as cooks darker, and at a certain point gets overtaken by bitterness. Its freezing point depression factor increases in the early stages of cooking, as the sucrose breaks down into monosaccharides. But as cooking progresses, larger molecules form, reducing the freezing point depression. Light-to-medium caramels can probably be treated like invert syrup.
Molasses is unrefined syrup centrifuged off from sugar cane syrup after it crystalizes. It contains all kinds of stuff, including water, so it’s best to use in small quantities just for flavor. The primary sugar component is sucrose.
Maple syrup is also useful as a flavoring. Like molasses, its primary sugar is sucrose (typically 52%), and it contains water (typically 45%) plus around 3% invert syrup.. It’s not easy to know precisely how much water is in there, since syrup is boiled down to whatever level the maker desires. Fortunately, a little goes a long way. Grade B is the most flavorful. The grade signifies darkness and not quality; annoyingly, many grocers don’t know their trade and stock only the inferior Grade A. It’s worth it to find a reliable local source of the good stuff. Maple syrup is so expensive these days, you should get all the flavor you can from every ounce.
In the next post we’ll explore the dark arts of stabilizers.
Appendix 1: Invert Syrup
How to make Invert Syrup
Most professional kitchens just buy the stuff.
So—What is Invert Syrup?
Sucrose is a disaccharide, meaning a sugar molecule made up of two smaller monosaccharides: glucose and fructose. When we make invert syrup, we split these two monosaccharides apart, with the addition of water—a reaction called hydrolysis. Hydrolysis can occur with just the addition of water and heat, but an acid catalyst improves the efficiency of the reaction.
Typically, we can split (invert) about 85% of the sucrose. Manufacturers may be able to invert more of the sugar, by using other chemical or enzymatic catalysts.
When you cook your own, you control the final water content with the cooking temperature. Cooked to 113°C–114°C the final syrup will contain a bit under 20% water. This is dry enough to work in ice cream without adding too much water, and gives a long life in the fridge. But it’s not unreasonably gluey.
This inversion of polarized light has no known application in the kitchen. Not even Nathan Myhrvold has suggested that we run out and buy a polarimeter. Just try to remember that inverting sugar does not mean turning the bag upside-down.
Appendix 2: Sample Recipe
Quartet of Dark Sugars Ice Cream
I’ve written this for cooking in an immersion circulator, but it adapts fine to the stovetop or other heating methods.
25g maple syrup
10g (2 tsp) alcohol-based vanilla extract
-set immersion circulator to 75°C
-add yolks, cream and vanilla extract.
Milk Fat: 11.3%
Total Solids: 37.4% (a little lower than ideal)
Solids Nonfat: 25.3%
Milk Solids Nonfat: 10.6%
Egg Lecithin: 0.29%
POD: 114 / 1000g
PAC: 263 / 1000g (a little higher than ideal)
Appendix 3: FPDF, PAC, Absolute PAC
Problems in Quantification