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.
Dextrose 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 invert syrup are 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 invert syrup can bring the softness and smoothness back.
Remember that invert syrup is only about 80% sugar solids by weight when you calculate the solids in your recipe (the rest is water). See notes on invert syrup below in the appendix.
Fructose is the monosaccharide, which, along with glucose (dextrose) makes up both table sugar and invert syrup. It has the same high freezing point suppression of dextrose, but is much sweeter—about 25% sweeter than table sugar, 80% sweeter than dextrose. We could use fructose, like invert syrup, as one of the controls of relative sweetness and freezing point.
Fructose is a more powerful ingredient than invert syrup. It offers more control (because its sweetness is in such high contrast relative to dextrose), it contributes no water, and it’s easier to handle (it’s powder, not goop). Howerver, it’s significantly more expensive than invert syrup, and has never been adopted as a staple among pastry chefs. So it’s a non-standard ingredient. I suggest you get you get some. A little goes a long way.
If you’d like to try substituting dry sugars for invert syrup, just leave out the invert syrup, and replace with dextrose and fructose. Each of these sugars should be measured to 40% the weight of the invert syrup. So if the recipe called for 30g invert syrup, replace it with 12g each dextrose and fructose. This is in addition to any dextrose that’s already in the recipe. Mix in with all the other dry ingredients.
Then the tweaking begins:
Does it need to be less sweet? Increase the ratio of dextrose to invert syrup. If that’s not enough, Reduce the sucrose and increase dextrose by 0.75 times the change in sucrose.
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.
Finally, are there flavoring ingredients that will directly effect the freezing point—namely alcohol? If there’s a lot, the ice cream may need all the help it can get to harden enough. Eliminate the glucose. Reduce the sucrose, too, if there’s any room to lower the sweetness. Add a bit of nonfat dry milk to get th solids up, and increase the stabilizers. We’ll discuss this in detail in a future post on booze flavors.
Other Important Structural Sugars
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 flavors which by their nature are low on solids, and so need something to combat their innate wateriness—typically sorbets like lemon and watermelon. These flavors are built from fruit juices that are mostly water. We’ll address sorbets generally in another post.
As a bulking ingredient, I usually prefer milk solids to maltodextrin, since 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.
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.
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.