Tuesday, May 31, 2016

Ice Cream Stabilizers

Shunned and embraced, demonized and defended, shouted and mispronounced, these ingredients are the most widely missunderstood, proving equally befuddling to ice cream lovers on all sides of the never-ending, stupid lively arguments. I’m hoping to shed some light here.


What Are They?


Stabilizers are any ingredients used to thicken the water in ice cream. They make ice cream smoother, by slowing the growth of ice crystals. And they can improve the texture generally, by adjusting the body, the speed of melt, and the finish.

Technically, they are hydrocolloids — suspensions of fine particles in water that form a network, increasing the water's viscosity, and in some cases forming a gel. When you thicken gravy with flour, make pudding with cornstarch, or mix Jell-o, you’re making hydrocolloids. Which is to say: you’ve probably been using stabilizers for a long time. 

Properly stabilized ice cream not only resists developing an icy texture over time, but will actually form smaller ice crystals to begin with.1 Improperly stabilized ice cream (like improperly cooked food) can indeed be awful. We'll be discussing how to use these ingredients well, with the belief that in most cases, it's possible to make a better ice cream with stabilizers than without.

Stabilizer Examples:


Egg Custard. Custard is indeed a stabilizer. It’s among the most effective at creating great textures, but only middling at slowing ice crystal growth. This is likely because custards exhibit synerisis, or weeping: they let water seep out of their gelatinous structure. The smoothest egg custard ice creams use additional stabilizers. Custard's other drawback is that it damps the release of flavors more than most other stabilizers—especially lighter and more aromatic flavors, and water-soluble flavors (fruits, etc.). 

Custard viscosity varies with the concentration of yolks and cooking temperature. For thickening and stabilization, ice cream requires at least 3% egg yolk by weight, which is between 1.5 and 2 egg yolks per liter. 4 to 6 yolks per liter is more common, and some people go higher, making a dessert that's more a frozen custard than an ice cream, with egg flavors and textures dominating.

Cooked egg flavor, like viscosity, increases with concentrationand cooking temperature, and possibly also with cooking time. With yolk concentrations below 4%, eggy hydrogen sulfide compounds will probably be undetectable except after extreme cooking. For more egg-rich recipes, it may be beneficial to keep the cooking temperature between 70°C and 72°C for longer cooking, or below 82°C for shorter cooking.


Refined Starches, like cornstarch and tapioca, are a staple in many ice cream traditions. Cornstarch is most famously used in Southern Italian gelatos, which are often made without eggs or even cream. It’s become popular in many home recipes because it’s easy to find and easy to use, and gives reasonably good texture and stability. Tapioca works similarly. Starches generally give better flavor release than custard, but not as good as gums.

I’ve seen some recipes that use arrowroot starch, which is possibly the best of the refined starches for savory applications, but should be avoided in ice cream. Arrowroot reacts with dairy ingredients to create unpleasant, snot-like textures.


Gelatin is the oldest known non-egg ice cream stabilizer. And it’s a very good one. Its ice crystal suppression and texture make it arguably superior to starches, and it’s equally easy to use. Gelatin has fallen out of favor partly because of cost, and partly because it’s an animal product. Even non-vegetarians are occasionally skeeved by knowing their ice cream contains rendered beef and pork tissue. But I would still encourage experimentation with gelatin, if you want to play with stabilizers but aren’t ready yet to buy a whole arsenal of hydrocolloids from the molecular ingredient sites.

Gums


These are the mack-daddy stabilizer ingredients. They work in minute quantities, have superior powers of ice crystal suppression, offer almost infinite textural possibilities, have no detectable flavor of their own, give superior flavor release (they don’t mute the flavors of the ice cream), and can be almost endlessly confusing.

We’re going to look at a small selection of gums individually, although much of the strength of gums comes from their synergies; they work best in combinations. The synergies are often such that the gums reinforce one another, and offer capabilities in combination that they did not offer individually. 1 + 1 = 3, etc.

The challenge in creating a gum blend lies is balancing the qualities of the individual gums with each other, as well as with the rest of the recipe, while taking into account the various synergies between those individual gums.

Gums are all polysaccharides—big molecules made up of lots of small sugar molecules linked together. They are close cousin to starches ... you can think of them as superstarches.

Locust bean pods

Locust Bean Gum, also called carrob bean gum, is made by milling the seeds of the locust tree. It’s been used as a thickener since at least 79 AD, and possibly much longer (look up traditional Indian recipes for cluster beans, another name for guar. They eat it by the bowl. We'll be using it by the milligram). LBG has the most powerful ice crystal suppression of all the conventional gums. It favors a smooth, creamy, natural texture that does not draw attention to itself. It manages this by forming a weak gel that is stable while frozen, but that is highly shear-thinning, so once the ice cream melts and starts moving, most of the added viscosity vanishes. These characteristics make it the most important of the gums in ice cream.

LBG needs to be heated to hydrate. Most varieties require heating above 80°C, which is higher than ideal for many ice cream processes. Varieties sold by TIC gums and Willpowder hydrate at much lower temperatures.


Guar beans

Guar Gum is milled from the seeds of the guar plant, which is a legume. Guar gum is chemically similar to locust bean gum, and the two are often used together. Guar is not quite as effective as LBG at ice crystal suppression, but gives greater viscosity than LBG at similar concentrations. In combination, guar and LBG strengthen each other—when using the two together, you can use a lower total quantity of gums.

Guar gum has only been in use since the 1950s, but the guar bean has been cultivated in India as a protein source for hundreds of years.

Guar’s main use, besides strengthening the effect of LBG, is to add body. In high concentrations, it can make ice cream that’s chewy and elastic—either a flaw or a benefit, depending on your point of view. In New England, they like a lot of guar.

Irish Moss / Carrageenan
Carrageenans are extracts from Irish Moss seaweed (chondrus cripus). They’ve been used as food thickeners since the 15th century. Modern versions of carraggeenan are divided into types based on the details of their molecular structure. The most common in the culinary world are Kappa, Iota, and Lambda. These types have different solubility temperatures, gelling characteristics, and interractions.

The most useful type in high quality ice cream is Lambda Carageenan, since the others form gels in the presence of calcium (dairy products). See note on gels, below).

Carrageenan has a moderate effect on ice crystal suppression, and a strong effect on texture, especially of the melted ice cream. Carageenan creates a rich and creamy mouthfeel similar to egg custard, but does so without adding any flavor of its own, and without muting other flavors. 

Carrageenan’s secondary role is to prevent wheying-off, a phenomenon of milk proteins preciptating out of suspension, aggregating, and creating grainy textures. Locust bean gum and carboxymethylcellulose can induce whey-off, so when these stabilizers are used you’ll usually see at least a minute amount of carrageenan.

Giant kelp / brown algae. Where we get the alginate.
Sodium Alginate is another seaweed extract, made from a brown seaweed grown in cold water areas. It’s a popular stabilizer, especially in low-fat and fat-free ice creams, because it forms a gel in the presence of calcium ions in the dairy. Its gelling quality makes it less useful in standard recipes (see the note on gels, below). The gel breaks into a fluid gel when the ice cream is spun, creating a unique body and viscosity. It’s quite effective at ice crystal suppression.

Sodium Carboxymethyl Cellulose: a big-ass molecule

Carboxymethylcellulos, also called cellulose gum, technically called sodium carboxymethylcellulose, is synthesized from plant cellulose. It may have the strongest ice crystal suppression of any known gum. It adds body and chew comparable to guar, and is synergistic with locust bean gum, guar, and carrageenans—it forms a gel in combination with these ingredients, with can be problematic (see note on gels, below).

There are low-viscosity varieties of CMC that suppress ice crystal formation with very little increase in base viscosity, if they're used in a non-gelling blend. These theoretically allow you to control iciness and texture completely independently. Examples include TIC Gums CMC PH-15.

CMC is not popular in higher quality ice creams, because it is a synthetic ingredient. While the word “natural” is rather ambiguous, CMC lies outside most interpretations of natural. This is perhaps more a marketing issue than a real one—there are no health concerns associated with the stuff. It's just a big polysaccharide like the gums that come from ground up seeds. Nevertheless, I’ve only experimented with it once and was dissuaded by its gel-forming with other gums.

You can get xanthan at the supermarket these days.

Xanthan Gum is created by bacterial action, when the organism Xanthomonas campestris chomps on glucose, lactose, or table sugar. It’s a fermentation product, much like cheese and booze. 

Xanthan is often called the “wonder gum,” because it’s easy to dissolve at any temperature, it thickens at any temperature, works at a wide range of acidities, can tolerate alcohol, freezing, thawing, and just about anything else.

While most gum recipes require a scale that reads to 0.01g and careful dispersion and heating, cooks find xanthan pretty friendly in an old-fashioned-ingredient way. Need to stabilize a vinnaigrette? Toss in a pinch of xanthan and whisk until it’s dispersed. Want to add a bit of body to a sauce? Make a slurry with a pinch of xanthan, and whisk in just as you would with cornstarch or arrowroot. 

Xanthan is not, however, my first choice in ice cream stabilizers. It does an acceptable job, but is not the most powerful ice crystal suppressor. And it forms a gel when used with locust bean gum. This makes the mix harder to handle. See note on gels, below. I do recommend xanthan for anyone interested in starting experiments with stabilizers. You can get it anywhere now, and it’s worth having around for a million other uses.

Dondurma vendor offering a cold chew.
Salep, Mastic, Gum Arabic, and Konjac Flour are specialty stabilizers used in Dondurma, a traditional taffy-like ice cream popular in Turkey and Azerbaijan. Also called Maraş, this ice cream is both chewy and resistant to melting. Salep (flour made from the root of the Early Purple Orchid), and Mastic (hardened sap the Mastic Tree) are traditional. Gum arabic (hardened sap of the Acacia Tree) and Japanese konjac flour (starch from the Konjac, aka Elephant Yam) are more readily available substitutes.  A combination of gellan gum (a microbial gum like xanthan, which forms gels) and guar can also substitute



Denatured Whey Proteins: Some of the whey proteins, which make up 20% to 25% of the total protein in milk and cream, can form a gel-like network when heated to the right temperature for the right amount of time. This network functions in the same way as the other hydrocolloids discussed here. Whey proteins may also be denatured chemically or enzymatically, using processes that are probably out of reach in the home and pastry kitchen. We don't know what they do at Haagen Dazs, but they're doing something. See extended discussion in the post on Emulsifiers.




Blends and Variations



Blend 1: Easy-to-find ingredients

Gelatin : Xanthan Gum

3 : 1

1g gelatin 0.33g xanthan For 1 liter of ice cream (0.15% total)


Gelatin hydrates when cooked to 60°C / 140°F. Any standard cooking step will take care of this.

Both the gelatin and the xanthan suppress ice crystals and increase the viscosity of the mix. 

The gelatin forms a weak gel that melts at body temperature and strengthens in the cold, so its effect is most pronounced on the ice cream in the frozen state. The xanthan gum’s activity is almost completely independent of temperature. So its effect is most pronounced on the ice cream in its melted state. So if you want more body, increase the proportion of the gelatin. If you want a creamier melt, increase the proportion of xanthan.

You can experiment freely, but be warned that at much higher concentrations, xanthan’s mouthfeel goes from creamy to slimy. If you’re not getting the results you want from this blend at modest concentrations, you should move on to the other gums.



Blend 2: General Purpose

Locust Bean Gum : Guar Gum : Lambda Carrageenan

4: 2 : 1

0.8g  0.4g  0.2g  for 1L  (0.15% total)

Mix should be cooked at least to the hydration temperature of the locust bean gum. TIC Gums versions hydrate at 74°C / 165°F—most brands hydrate at temperatures higher than what’s ideal for most ice creams. 

All three gums suppress ice crystals and affect texture, but not equally.

The Locust Bean Gum is the most powerful at suppressing ice crystals. It has a subtle effect on increasing the body of the ice cream and the creaminess of the melt.

The Guar amplifies the power of the locust bean gum, and has the strongest effect on the body of the frozen ice cream. Significantly increasing the guar will make the ice cream chewy and elastic.

The Lambda Carrageenan has the strongest effect on the consistency of the melted ice cream. Its mouthfeel is similar to that of custard, although it has a somewhat cleaner finish. If the melt feels too milky or watery, you can subtly enrich it with a bit more LCG.

I use this blend at 0.15% in a 15% milk fat ice cream that uses 2 yolks per liter. For a richer, more custardy mix, you could experiment with using as little as 0.1%. For a lighter ice cream, or one that needs a long shelf life, you could try 0.25%



Blend 3: Eggless Ice Cream

Soy Lecithin: Locust Bean Gum : Guar Gum : Lambda Carrageenan

10: 4: 2: 1

3g 1.2g  0.6g  0.3g  for 1L  (0.5% total)

Mix should be cooked at least to the hydration temperature of the locust bean gum. TIC Gums versions hydrate at 74°C / 165°F—most brands hydrate at temperatures higher than what’s ideal for most ice creams. 
This is the same as the standard formula, but increased 50%, and with soy lecithin added. Egg custard has thickening and stabilizing benefits, so its elimination requires a higher concentration of gums. The eggs also act as emulsfiers (see the next post).

The lecithin content of this blend is equal to two large egg yolks. You could use less—as little as 1/5 this much. I specify this quantity because egg-free bases are most useful when using ingredients that add a lot of fat—like chocolate. In these cases, some extra emulsifier can help ensure a smooth texture.

All the notes for manipulating the standard formula apply here. Be careful if increasing the lecithin. You probably don’t have to. If you go too far, it will actually impede the whipping of the ice cream.



Blend 4: Sorbet

Locust Bean Gum : Guar Gum : Iota Carrageenan : Lambda Carrageenan

4: 2: 2: 1

1.33g  0.66g  0.66   0.33g  for 1L  (0.3% total)


This should be blended into the syrup portion of the sorbet, and brought to a simmer. At this point, flavors can be infused into the syrup (sugar syrup is a powerful solvent for both polar and non-polar flavor molecules). Syrup should be chilled for several hours to allow gums to fully hydrate. Then it can be mixed with chilled fruit puree and frozen into sorbet.

This is similar to the standard formula, but with iota carrageenan added, and total gum quantity doubled. Sorbets have no cream, and are low on solids. They have little to no inherent creaminess, and a lot of water to stabliize. The iota carrageenan forms a weak gel in combination with the locust bean gum, adding viscosity and body. The gel breaks easily into a fluid gel under shear and then re-forms. It's freeze-stable and helps give a creamy texture.

Most sorbets have no fat content and so have no need for emulsifiers. If you wish to make a sorbet with chocolate, nut butters, olive oil or other fatty ingredients, you may get smoother results by adding some lecithin (maybe start with 1.5g / Liter).

We'll look at all this in greater depth in a future post on sorbets.


Notes on Using Gums


Three aspects of gums demand attention: measuring, dispersing, and hydrating.

They can be tricky to measure for small batches because the quantities are minute. You should have, in addition to a higher capacity scale, a small scale that reads to 0.01g. There are many available on Amazon and Old Will Knott Scales for under $40. 

I use a small cup or bowl, and use it to weigh all the ingredients that total less than a few grams. This typically includes the stabilizers and the salt. After the ingredients are measured out, I stir them together, and then thoroughly mix them into to the other dry ingredients (sugars, dry milk, etc.). This helps with dispersion:

Dispersion means mixing the dry ingredients into the wet ingredients evenly, without clumping. Gums make this tricky. So does milk powder. The first defense against clumps is to thoroughly stir all the powdered ingredients together. Locust bean gum will only clump with locust bean gum; dry milk will only clump with dry milk, etc.. So if you mix all the powders together, including the sugar (which makes up a lot of bulk and doesn’t clump at all) you can keep the individual powders separate long enough for them to disperse without clumping.

The second defense is proper use of a blender. Adjustable speeds are handy for this: start on the lowest speed that makes a vortex down the center of the blender jar, and pour in the dry ingredients. Once they’re in, crank the speed all the way and blend for a minute or so. Thorough dispersion is required for thorough hydration:

Hydration, of course, means soaking up water. Gums don’t do anything until they’re hydrated, and many of them need time, or heat, or both. Lambda carrageenan hydrates fairly quickly at room temperature. Guar hydrates at room temperature but can take over an hour to reach full viscosity. Locust bean gum needs to be heated, to 74°C–85°C, depending on brand. It may take many minutes at temperature to hydrate fully. 

Some pastry chefs, including Francisco Migoya, save time by mixing a large batch of stabilizer. Then it can be stored and measured out as a single ingredient, like a commercial blend. This approach demands throrough mixing. It makes the most sense if you use the same stabilizer blend most of the time.

If you experiment, pay special attention to the finish—the flavors and textures left behind in your mouth after swallowing. A successful stabilizer blend won't be detectable. The ice cream flavors should linger and continue to develop, but shouldn't be indelible. The feeling of creaminess should gradually dissipate. It should not devolve into pastiness or stickiness. These kinds of textural flaws point to over-stabilization, or to poor choices in stabilizing ingredients. I like the locust-guar-lambda blend as much for its transparency as for its effectiveness.

Note on Gels


Some common stabilizer ingredients form a gel in ice cream. Examples include Sodium Alginate and Kappa Carrageenan (which gel in the presence of the dairy's calcium). Other ingredients form gels in combination with each other. Examples include xanthan gum with locust bean gum, locust bean gum with kappa or iota carrageenan, and carboxymethylcellose with locust bean gum, guar gum, or any carrageenans.

Gels are solids that exhibit properties of a liquid. Technically they are colloidal dispersions in which the solid forms the continuous phase, while the liquid (we're always talking about water in the ice cream world) forms the dispersed phase. The solids create a network, with either physical or chemical bonds, and typically work in very small quantities—often less than 1% the weight of the water.

Gels can be strong or weak, yielding or elastic, brittle or tough, high or low viscosity. Under shear, some gels exhibit brittleness and crumble (like flan), others stretch and bounce back (like gel-o), others deform (like clay), others form a fluid gel that after sheer reforms into a gel (like iota carrageenan), others form a fluid gel that after sheer stays fluid (like agar).

To gel or no to gel? For most ice creams, I prefer  non-gelling stabilizers. They tend to have a less intrusive texture, and to work more predictably, and to be easier to handle. Often with gelling stabilizers, the mix will be too thick after aging to spin efficiently in the ice cream machine. It will have to be thinned with a blender first, turning it into a fluid gel. If possible, I like to avoid this added step.

If you're making low-fat or fat-free ice creams, or sorbets, gelling stabilizers become useful. They can add body and creaminess that's often lacking in these recipes. 

Closing Thoughts


I hope this post has made a case for the usefulness of stabilizers—of custard, at least, but preferably something with a bit more effectiveness and flexibility. The questions should be about how deeply involved you want to get.

Commercial blends are easy to find and easy to use. They go into many of the world’s best ice creams every day. Pastry chefs who know more than i do—about basically everything—rarely have a clue about the level of hydrocolloid micromanagement we’re discussing here. So why bother rolling your ownI?

Well, you’ve read this far, so you’re probably a geek who likes to tinker under the hood of the world generally. And you may appreciate the level of control afforded by the DIY approach. Blending your own stabilizer is like the next step beyond using curry powder from the supermarket—discovering that there are a dozen spices in there, that they can be varied by proportion and by how they’re added to the dish. 

I have another motive, inspired by my days as a darkroom-obsessed photographer. In any technological medium, your creative process can become dependent on proprietary manufactured products. And when these products are discontinued, or “improved,” you’re screwed, at least until you scramble to figure out an alternative. I learned the hard way the benefits of mixing my own formulas from generic ingredients, after watching some favorite photographic papers and developers vanish. I gradually weened myself from proprietary stuff whenever possible. The kitchen's no different. A company like Cuisine-tech could stop making Cremodan tomorrow—but someone’s always going to be selling plain old locust bean gum.

In the end, stabilizers are just ingredients like any other. If they seem daunting, it’s only because textbooks and cookbooks and culinary websites haven’t addressed the topic adequately. Until they do, I hope the information here proves useful.




Appendix


Ingredient sources

Kalustyans (In NYC ... better to visit than to suffer their web store)


For further reading

Ice Cream, 7th Edition, H. Douglas Goff, Richard. W. Hartel. p. 75–82
Stabilizer Blends and their importance in Ice cream Industry 


Ask the experts

TIC Gum Gurus: (800) 899-3953
CP Kelco support: 1 (800) 535-2687

(The tech support people at both companies, when I've called, have been exceptionally friendly women, completely over-qualified—probably chemistry PhDs,—and have seemed happy to talk ice cream. If you're nice they may send you product samples.)


1"Microscopic investigation revealed that stabilized ice cream (locust bean gum and carrageenan) had significantly smaller mean ice crystal diameters both initially and as a result of heat shock and storage (24 weeks) compared to those of ice cream without stabilizer. However, the differences grew larger over time."
—Caldwell, K. B.; Goff, H. D.; and Stanley, D. W. (1992) "A Low-Temperature Scanning Electron Microscopy Study of Ice Cream. II. Influence of Selected Ingredients and Processes," Food Structure: Vol. 11: No. 1, Article 2.
Available at: digitalcommons.usu.edu/foodmicrostructure/vol11/ iss1/2





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
Part 11 of this series: Introduction to Flavor
Part 12 of this series: Ice Cream Flavor: Coffee

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 other sugars.

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 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.

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.

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 October, 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
Part 11 of this series: Introduction to Flavor
Part 12 of this series: Ice Cream Flavor: Coffee