Monday, May 30, 2016

Sugars in Ice Cream



Sugarcane


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. 


Personal narrative and manifesto: 

The quick fix would be to add more sugar, but most ice creams are too sweet already. A typical home recipe is 17% or more table sugar by weight: kid stuff. You cannot taste any subtlety through cloying sweetness—you can’t taste the dairy, and you can’t taste any of the more delicate, aromatic flavors we’re going to work so hard to put in there. 

It’s not just home recipes. Haagen Dazs is too sweet. Ben and Jerry’s is too sweet. Talenti is too sweet. Cold Stone is too sweet. Every small town “homemade” ice cream shop I’ve ever wandered into: too fricking sweet. 

I once managed an ice cream shop in Colorado, making ice cream that the owners and I were proud of. It was too goddam sweet, of course, but I had no reasonable frame of reference, until after I’d quit and taken a trip to Paris, where I was lucky enough to be invited to dinner at Taillevent—a restaurant which at the time had three Michelin stars and which had once been considered the finest in the city. After uncountable savory courses, we were put in the hands of pastry chef Gilles Bajolle, who would soon become the first chef that I’d shamelessly steal or reverse-engineer recipes from. He was most famous for his marquise au chocolat with pistachio crème anglaise (which indeed I stole and worked on for many years) but the dish that opened up the heavens for me was the single unadorned quenelle of thyme ice cream.

There’s nothing surprising today about an herb flavored ice cream. But back in the 20th Century, for someone who’d been making flavors like “rocky mountain road,” an herb flavor besides mint was a sucker-punch to the imagination. And the flavor itself: let’s just say that I took a bite and sat there, very quietly, for a long time. The sensations kept developing, unfolding, surprising, telling stories. It was obvious that this was the first truly good ice cream I’d ever had. 

Only later did I realize that one of its secrets would be easy to duplicate: make the ice cream less sweet. Let the herbs and the dairy do what they do.

End Rant.


The Problem


Conventional ice cream is too sweet, but reducing the sugar content makes it too hard at serving temperatures.

The Solution


Use different sugars.


Michael Laiskonis, former executive pastry chef at Le Bernardin and current Creative Director at the Institute of Culinary Education, taught me how to think about using sugars. 

Freezing point suppression is dependent on the molecular weight of a dissolved ingredient. The lower the molecular weight, the smaller the molecule, and so the more molecules per gram—and the greater the reduction of the freezing point.  Consider the following table:




The sugars we care most about are sucrose, dextrose, and invert syrup. 

Sucrose is table sugar. Since it's the most familiar, and has the flavor we most expect, we use it as our foundation. It also provides a frame of reference for understanding the other sugars.

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! 

Invert syrup is a liquid sugar that I think of separately. It’s slightly sweeter than sucrose, and offers slightly stronger freezing point suppression, but the differences are too small to matter much. Invert syrup is fantastically useful, however, as a texture modifier. It adds a bit of body, and suppresses the growth of ice crystals—much like milk solids and stabilizers. And it does so while acting as a sweetening ingredient. It does all this without any downsides. 

It’s 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.

In Practice

My starting point is 13% sugar by weight (not counting the lactose in the milk).

The blend consists of:
60% sucrose 
26% dextrose
13% invert syrup

So, as an example, if the total recipe is 1000g, we start with 130g sugar:

78g sucrose
34g dextrose
17g trimoline

Then the tweaking begins:


Does the ice cream need to be softer? Reduce the sucrose and increase the dextrose by 1.33 times the change in sucrose.

Does it need to be less sweet? Reduce the sucrose and increase dextrose by 0.75 times the change in sucrose.

Are there ingredients that add fats which could harden the ice cream—like chocolates or nut butters? If so add more invert syrup, and subtract an equal amount of sucrose. (My chocolate ice cream’s sugar blend is over 40% invert syrup, with no sucrose beyond what's in the bittersweet chocolate).

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.

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. We could use fructose, like invert syrup, as one of the controls of relative sweetness and freezing point.

Fructose, in combination with dextrose, can replace invert syrup. This has the advantage of adding no water to the recipe (invert syrup is typically around 20% water) and is also a little easier to handle. Invert syrup is a sticky goo that clings to spoons and fingers and has a finite shelf life. I've asked a top-shelf pastry chef why this isn't a popular solution, and he said, simply, that he has invert syrup in the pantry, because he uses it for a million things. He doesn't have other uses for fructose.

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.

Variety Sugars

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.

Non-Caloric Sweeteners

It’s not easy, but it’s possible, to make decent sugar-free ice creams. The trick is finding ingredients that taste like sugar, adequately suppress the freezing point, and won’t give you a bellyache. 

By these standards, the perfect ingredients do not exist—although some of the sugar alcohols, like erythriol, come pretty close. We’ll discuss these in a later post (although I’m no expert on the topic).


In the next post we'll explore the dark arts of stabilizers.



Appendix 1: Invert Syrup


How to make Invert Syrup

250g sucrose
120g water (approx)
0.25 – 0.5g citric acid or cream of tartar (tartaric acid)


Mix ingredients in a saucepan and bring to a boil.

Once the mixture boils wash away any sugar crystals stuck to the side of the pan with pastry brush dipped in water. Water from the brush won't affect the outcome.

On medium heat without stirring boil the mixture to 235°F / 113°C. Remove from heat and cover the pan. Let cool at room temperature until it’s reasonably safe to handle. transfer to plastic container. Store in a refrigerator. Invert sugar will last at least a few months. 

You can melt and re-cook it if starts to crystalize. Toss it if you see mold.

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. 

The stuff is great to have around. In addition to magic it works on ice cream, substituting about 10% invert syrup for sucrose in most desserts will improve moistness and add shelf life.


Why is it “Inverted?” 

This may be the most useless piece of knowledge in the entire blog series. But you asked. 

Chemists measure the composition of optically-active solutions with a polarimeter, which passes plane-polarized light through the solution being measured. When the solution contains sucrose, the light rotates to the right. When the solution breaks down to glucose and fructose, the light rotates the other way, hence the inversion: 

C12H22O11 (sucrose, Specific rotation = +66.5°) + H2O (water, no rotation) C6H12O6 (glucose, Specific rotation = +52.7°) + C6H12O6 (fructose, Specific rotation = −92°) net: +66.5° converts to −19.65° (half of the sum of the specific rotation of fructose and glucose). 

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 wanted to create a recipe that gets all its flavor from the sweeteners, and that explores the possible depth and range of those flavors. It uses caramel, molasses (from the dark muscovado sugar), maple syrup, and chestnut honey. This ice cream has a lot of layers. Background hints of vanilla and salt take it even farther. It's not kid stuff—it isn't even especially sweet.

Muscovado sugar is a semi-refined brown sugar that's heavy on molasses and has a deep, complex flavor. Chestnut honey is dark, bitter, and challenging. For the maple syrup, look for one marked "Grade B", which is darker and more flavorful than grade A. The grade has nothing to do with quality.

I've written this for cooking in an immersion circulator, but it adapts fine to the stovetop or other heating methods.


Makes 1 to 1.3 liters

55g dark muscovado sugar
50g nonfat dry milk

3g salt 
0.8g locust bean gum (TIC or Willpowder)
0.4g guar gum
0.2g lambda carrageenan

35g (approx) water
35g granulated sugar
30g (approx) water

460g  whole milk
2 egg yolks (36g)
27g chestnut honey 
25g maple syrup

270g  heavy cream
10g (2 tsp) alcohol-based vanilla extract


-thoroughly stir together muscovado sugar, dry milk, gums, and salt.
-set immersion circulator to 75°C

-heat 1st portion of water and granulated sugar in a saucepan. Cook to medium-dark caramel.
-turn heat low. Deglaze with second portion of water. Water will boil off and caramel will clump.
-when water is mostly gone, add milk and stir to disolve caramel. Stir in the honey and maple syrup.

-pour milk mixture into blender.
-set blender speed to create a vortex; add powdered ingredients. cover and blend on high for 30 seconds to disperse the stabilizers.
-add yolks, cream and vanilla extract.
-briefly blend again on high speed.

-pour mixture into 1gal ziplock bag.
-add weight (recommended, to keep bag from floating) and evacuate the air.
-cook in water bath for 45 minutes to set custard, hydrate stabilizers, denature milk proteins.
-gently agitate bag after 5 and 15 minutes. if you see air accumulated in the bag after 15 minutes, release it, and carefully reseal bag.
-mix will be pasteurized (pasteurization time after reaching this temperature is under 2 minutes).

-remove bag from water bath. open and pour hot mix into clean blender container (or a square container if using a homogenizer or stick blender). remove weight (with tongs). use bag to squeegie off any mix. temporarily seal bag and keep handy. 
-blend on highest speed for 30 seconds to homogenize. 
-pour mix back into ziplock bag.

-chill bag in ice water bath (use ice bath to evacuate the air when sealing bag). carefully agitate to cool. Try to cool to refrigerator temperature. 
-refrigerate at least 4 hours, below 38°F / 3°C to age mix / pre-crystalize fat.

******
-pour into ice cream machine: snip off bottom corner of bag, and squeeze out mix as if using a pastry bag. or squeeze out into an intermediate container that’s easy to pour from.
-spin in the ice cream maker. With a mulitispeed machine, use a slow setting (this recipe works best with a low overrun). Ideal drawing temperature is 23°F / -5°C.

-harden in a blast freezer for several hours, or overnight in a cold standard freezer (should be set to -5°F / -20°C or lower). Ice cream will have to warm up several degrees before serving. 20 to 30 minutes in the fridge works well. Ideal serving temperature is 6 to 10° F / -14 to -12°C.



Shameless Plug:


Keep an eye out for my photography book on the Brooklyn Domino Sugar Refinery. To be published by Schiffer, Fall 2017.





Part 1 of this series: Introduction
Part 2 of this series: Components
Part 3 of this series: How to Build a Recipe
Part 4 of this series: Basic Recipe Examples
Part 5 of this series: Techniques
Part 6 of this series: Sugars
Part 7 of this series: Stabilizers
Part 8 of this series: Emulsifiers
Part 9 of this series: Booze
Part 10 of this series: Solids, Water, Ice


11 comments:

  1. David Lebowitz says use alcohol to soften ice cream. What's wrong with this?

    ReplyDelete
  2. I think Lebowitz is just trying to keep things simple for people. Alcohol works. But unlike sugars, it doesn't do anything to improve the ice cream's texture. By lower the freezing point without adding anything to improve body or stability, alcohol actually results in an icier ice cream, not a smoother one.

    In a later post I'll get into alcohol flavors—for these we add more nonfat milk solids, and change the sugar blend so we don't get too much softening.

    ReplyDelete
  3. First of all, thank you for sharing your knowledge on ice cream! Your articles are a pleasure to read and have taught me a lot.

    I have a quick question regarding invert sugar:
    Are the stabilizing & textural benefits of invert syrup attributable to its monosaccharide constituents, or is there some other underlying cause?

    Would I get the same effect by using a proportional amount of anhydrous glucose / fructose in place of invert syrup?

    ReplyDelete
    Replies
    1. Hi Paul,

      Sorry to take so long with a response. Your question has occurred to me before, and I've never been able to find an answer. There's no shortage of sources that go on endlessly about the benefits of invert syrup. None that I've found say why (or if) it's any different from a glucose and sucrose dissolved together.

      I'm waiting for answers from a couple of real chemists and will let you know what i find out.

      Delete
    2. Thanks for looking further into this.

      Anecdotally, glucose has been working well in my home experiments.

      Delete
    3. I asked chef Laiskonis your question. He doesn't see why it wouldn't work, and suggests trying it. The substitution isn't interesting to him, because as a pastry chef, he always has invert syrup on hand, but doesn't use fructose powder.

      I find the idea compelling, though—because it's easier to work with powdered ingredients than with a heavy syrup in ice cream. I haven't tried it yet, because to to set up a controlled experiment is difficult, and I don't have facilities for making identical, simultaneous batches of ice cream.

      I'm looking for a food scientist to ask.

      Delete
  4. "Quartet" recipe came out GREAT! My wife said it would probably pair with a nice stout!

    Boy, to think of all the failed batches I could have prevented eating if only I found this site first. So...many...calories...

    Not only is this the best technique around it is all explained in ways that make sense. Excellent job, I just wish you were able to post more often! (but grateful to get it when you're able)

    THANKS!!!

    ReplyDelete
  5. Anon, I'm so glad it worked out. That's one of my favorite recipes.

    ReplyDelete
  6. Thank you for sharing all these informations. However I'm wondering about the use of glucose, which is almost always used by professionnals, here in France.
    In contrary, dextrose is not recommended by french ice cream makers because it might significantly limit overrun. What do you think about this ?

    ReplyDelete
    Replies
    1. Hi Jerome, thanks for writing.

      Dextrose and glucose are interchangeable names for the same sugar. The only likely difference in practice is that products labelled Dextrose are (usually) the anhydrous or monohydrated powdered forms of the sugar. These versions contain little or no water.

      Sugar labelled Glucose, when sold in baking supply stores, is often either a syrup or "atomised glucose"—which is a powder made by spray-drying glucose syrup. Both of these products contain a lot more water than the Dextrose powder products.

      It's also possible that some products sold as Glucose are identical to Dextrose powder, but it can be hard to tell.

      The bakery glucose products typically add more water than we want to add to an ice cream formula, but the worse problem is that we often don't know how much.

      So it makes life much simpler to just use Destrose powder.

      As far as overrun, there's no difference between any of these, at least if you compensate for any added water. The sugar molecules are identical.

      Delete
  7. Thanks for taking the time to discuss this, would you mind updating your blog with more information? It is extremely helpful for me.

    Dry Ice Blasting in Dubai & Dry ice Dubai

    ReplyDelete