Thursday, June 9, 2016

Ice Cream Emulsifiers

This has so far been the most challenging post to research and write; there’s a lot of arcane and incomplete knowledge on the topic, much of it of questionable relevance to the mission of artisanal ice cream making. If you favor recipes with one or more egg yolks per liter of base, and don’t want extra homework, you can skip this one.

If you’re interested in making egg-free ice creams with the best possible texture, or are just a glutton for minutia, read on.



Electron micrograph of a milk fat globule. Here's where the action is.

Basics


An emulsifier is a two-faced molecule that binds to water on one side, oil on the other. You’ll see one side labelled hydrophilic, the other labelled either hydrophobic or oleophilic—different jargon, same idea.

The adage that oil and water don’t mix still holds true after all these years. This would be a problem for much of the world, especially the plant and animal parts, if it weren’t for emulsifiers helping to hold things together.

Like, for instance, milk. Milk is a colloid made from a polar chemical (water) and non-polar chemical (milk fat), which cannot mix. Technically speaking, they are not miscible. But they can form an emulsion—a more complex arrangement in which immiscible ingredients coexist, with some degree of stability.

Because it’s an emulsion, Milk is creamy, opaque, and homogenous. The fat molecules are divided into many microscopically small globules, which are surrounded by emulsifying chemicals that keep them from glomming together and rising to the top. These emulsifiers include fatty chemicals called phospholipids, and proteins called wheys and caseins.

We’re mostly interested in the caseins, which make up 20% to 25% of the milk proteins. They gather together in clusters called micelles, which expose their hydrophilic and hydrophobic surfaces on different, allowing them to bind both water and fat—thereby keeping the milk from separating.1 If you look at milk under an electron microscope, you see big round fat globules, covered in a thin membrane of casein micelles. This casein, with its hydrophilic end facing outwards, keeps the fat globules connected to the water and discourages them from joining each other.


Emulsifiers in Ice Cream


Milk Fat and Casein. Click to enlarge.

Left: fat globule with membrane made of casein micelles

Center: crystalized fat. Crystals protrude, but casein prevents them from bumping into other globules.

Right: crystalized fat partially destabilized by emulsifiers. Most of the protective casein is gone,
so the fat globules are better able to bump into each other and form a larger structure.


Thanks mostly to the casein, milk and cream are already pretty stable emulsions—so why are emulsifiers so important in an ice cream recipe?

The reason is that the milk and cream emulsions are a bit too stable. A big part of making ice cream involves the same process as making whipped cream, which requires destabilizing the emulsion. As long as the emulsion is stable, those fat globules can't join to create a foam network. With traditional methods, you can only whip cream containing over 30-something percent fat. With lower fat percentages, there’s enough water between the fat globules to keep the emulsion stable. Ice cream usually has far too little fat.

So to whip ice cream, you need extra help to partially destabilize the milk fat emulsion. Then the fat globules can partially coalesce—science talk for the fat glomming together just enough to form a stable foam.2

This is what added emulsifiers are for. They weaken the existing emulsion, allowing the ice cream to whip into a foam more easily, and with better texture and stability.



Ice Cream Emulsifying Ingredients



Egg Yolk


Egg yolks may be the most familiar emulsifier in the kitchen; they hold together mayonnaise, hollandaise and béarnaise family sauces, Caesar’s salad dressing, and chocolate marquises.

Yolks are usually cooked to a custard consistency, which also thickens the water portion of the ice cream (as a stabilizer—see the post on Ice Cream Stabilizers). Yolks are occasionally used without taking advantage of their thickening ability, but they must at least be cooked to the point of pasteurization.

Yolks contain a number of proteins and lipids that work as emulsifiers. By far the most important among these is lecithin. For adequate effect on ice cream emulsification, the mix requires 0.5% to 1% egg yolk. This equals 1/3 to 2/3 yolk per liter of mix, so a single yolk is more than adequate. 2 yolks (3 to 4%) are necessary to get significant thickening / stabilization. For the richest French custard-style ice creams, 4 to 6 yolks per liter is more common, with 8 to 10 being close to the outer fringe.

I would consider anything with 10 yolks per liter a frozen custard rather than an ice cream. Custard texture and flavor will dominate, or at least will compete heavily with everything else. 



Non-Egg Emulsifiers


The following are useful primarily if you’re making ice cream without eggs. Egg-free ice creams can be lighter, can have more vibrant flavors and a cleaner finish, and of course will be completely without egg flavors (although ice creams made with as few as two yolks per liter have essentially no egg flavor). Eliminating eggs can be especially useful in ice creams that have a lot of extra fat from the flavor ingredients: chocolate, nut butters, avocado, etc.  With these flavors, eliminating eggs is a way to to avoid the flavor damping and greasiness that can come with too much total fat content.

Lecithin
Lecithins are complex mixtures of fatty components derived either from eggs or soybean oil. They allow egg-free ice creams to be made with the same, all-natural emulsifier used in custard ice creams. Soy lecithin is as effective as egg lecithin and costs less. A single “large” egg yolk contains roughly 1.5g lecithin. An egg-free recipe can be made with 1.5 to 4.5g lecithin per liter (0.15% to 0.45%) Higher quantities may be helpful in recipes with lots of added fat.

It’s possible that in very delicately flavored ice cream, lecithin will have a detectible flavor of its own. I haven’t found this to be the case (I’ve tried straight soy lecithin out of the jar and found its flavor much milder than milk powder). Flavor may vary with the quality grade of the ingredient. Seek a high quality, very refined lecithin that has a mild flavor, and always disperse it thoroughly in a powerful blender.


Buttermilk Powder 
is similar to skim milk powder, but has a greater number of phospholipids that have emulsifying power. There’s some research into using this ingredient in place of traditional emulsifiers. I haven’t seen research on ice cream specifically, so I can’t recommend quantities or techniques. In larger quantities, it will of course taste like buttermilk. Buttermilk flavored ice cream might be good for first experiments.


Polysorbate-80
Is an emulsifier derived from oleic acid and from a form of sorbitan. It works in minute quantities, so it's both inexpensive and completely flavorless. It belongs to a family of emulsifiers called sorbitan esters, which are believed to be the most active at the fat interface of the ice cream, making them the most efficient at destabilizing the fat emulsion.3 

While the health scares you’ll read the internet are imaginary, I can’t find much compelling reason to use polysorbate in artisanal ice cream. Its advantages over lecithin and egg yolks are in cost and and improved whipability. Cost is a minor issue in small volume production, and most high quality ice creams are intentionally dense (low overrun) and so don’t need improved whipping. If you'd like to experiment, standard concentration is between 0.02% and 0.04%.


Mono- and Diglycerides
These are emulsifiers which occur naturally at very small concentrations in seed oils. Commercial products are manufactured, using a glycerolysis reaction between triglycerides and glycerol—components of fats from either plants or animals. This ambiguity concerning their source gets them flagged by some vegans, although there is no chemical difference in the end product. Because they complement each other, the mono- and di- versions are usually used together and packaged together. Unlike sorbitan esters, glycerides are believed to be most active at the fat-air interface, helping the ice cream form a finer-textured foam. I have not seen this confirmed by studies.

Versions for chefs are often packaged as “glycerin flakes,” although this is a bit of marketing nonsense, since there’s no glycerin in there. The vendors are fighting the bad reputation of ingredients that are manufactured or hard-to-pronounce. There is plenty of internet hysteria about emulsifiers—most of it dreamed up by charlatans like the Food Babe who deserve your active contempt. 

If you'd like to experiment, standard concentration is comparable to lecithin: between 0.1% and 0.2%.
3-D diagram of a ß-Lactoglobulin whey molecule.
When it denatures (cooks), it unwinds.



Denatured Whey Proteins
Whey proteins make up 20%–25% of milk’s protein content, vs. Casein’s 75%–80%. Whey is much less stable than casein when exposed to heat. At temperatures that are typical for pasteurizing ice cream and thickening custard, whey proteins begin to denature—they unfold from their original shape, exposing previously concealed surfaces to the molecules around them.

Another culinary term for using heat to denature proteins: cooking.

When the whey proteins denature, they expose rows of active, hydrophobic (water-hating / oil-loving) molecules to other proteins and fats they encounter. There are several different types of whey proteins in milk, all of which react differently to different temperatures and environmental conditions when they unfold.

In other words, this is complicated. Not only is my own understanding of the science imperfect, but the science itself, with regards to ice cream, is immature.

Here’s what we know: different types of whey protein denature at different temperatures. They partially denature over time above 60°C / 140°F. They don’t fully denature until they reach 90°C / 194°F or higher. When they fully denature, some may form insoluble aggregates that are harmful to the ice cream's texture. 

When they partially denature, they develop different kinds of molecular attractions. Some of them are attracted to the casein micelles. When they bind to the casein micelles, they form stronger bonds than the casein’s original bonds to the fat globules. When enough of this happens, the emulsion partially destabilizes—which is exactly what we use all those other emulsifying ingredients for.

Other denatured whey proteins are attracted to each other. At some temperatures they begin to form aggregates that make a gelatin-like network in the water phase of the ice cream. Which is to say, they behave like a hydrocolloid stabilizer (see the post on Stabilizers). 

What this tells us: we can, in theory, use partially denatured whey proteins as both an emulsifier and a stabilizer. Some industrial manufacturers, like Haagen Dazs, appear to get all of their stabilization from the whey proteins (although they use eggs as emulsifiers). Others, like Jeni’s Splendid, get all of their emulsification from the whey proteins (although they use starch as a stabilizer). In both cases, partially denatured whey proteins probably play a role in the ice cream’s body and texutre.

How much whey do we need? That's unclear, but a recipe that's high on nonfat milk solids is essential. You're not going to get enough from straight milk and cream. I'd suggest adding nonfat dry milk powder to raise the milk solids into the 10% range (which will improve the ice cream for many unrelated reasons as well).

What’s the optimum time and temperature to get these effects? It’s somewhere between 60°C and 90°C, half a minute and 90 minutes. There is no published definitive research on this, and what exists probably expresses ranges with varying characteristics and tradeoffs.

Back when Jeni’s made their egg-free bases in-house, in a big batch processor (as opposed to a continuous processor, which is more common in dairies and manufacturing plants), they cooked it at 75°C for an hour. That's a relatively low temperature and a very long time.

I cook my ice cream at 75°C for 30 minutes, plus 15 minutes for it come to temperature—for a total of 45 minutes in a heated water bath. This works well for my methods—but I’m not counting on the milk proteins for everything. I use gums to stabilize, and a couple of yolks (or some lecithin) to emulsify. I’m only counting on the proteins for some added body and smoothness. 

If you want to rely on the whey completely, you have some experimenting to do. You’ll probably need:

• a formula with a lot of milk solids
• fresh milk and cream that have been low-temperature pasteurized
• or raw milk, and the knowledge required to handle it without killing anyone
• nonfat dry milk that’s been spray dried at low temperatures

And you may need to cook different portions of the whey at different times and temperatures, to optimize them as both stabilizers and emulsifiers.


Ice Cream With No Emulsifiers
It’s possible to make ice cream with just cream, milk, and sugar, skipping the eggs and everything else. The result is called “Philadelphia Style,” although it doesn’t appear to have any roots or any particular following in Philly. This name may be the coinage of a 19th Century Journalist who needed a catch-all for East Coast ice creams that aren’t French. 


This is good news for the citizens of Philadelphia, since the name is rather slanderous. Philly-style ice cream can have vibrant, clean flavors, but it pays for them with a litany of texture defects: it’s icy, it rapidly gets icier, it whips poorly, the foam structure lacks smoothness (it can be grainy) and lacks stability (it deflates). Some people champion this style, and they’re lucky, because it’s easy to make. But I can’t think of other reasons to recommend it.


Closing Thoughts

Egg yolks work really well. If you don't want the flavor of eggs, or the flavor-dulling of heavy custard, you can use just a couple of yolks, or as little as half a yolk. If you really want to banish egg entirely, lecithin works nicely. I make eggless ice cream bases for flavors like chocolate and nut butters, where the flavor ingredients add tons of their own fat. In these cases a bit of lecithin (equal to what's in two or three eggs) and a bit of extra stabilizer takes care of the emulsion perfectly.

If you want to delve into the more efficient manufactured ingredients, there's a world of glycerides and polysorbates to play with. See the ingredient sources listed in the Stabilizers post. If you find any advantages to these ingredients in Artisanal ice cream, I'd like to hear from you.

You can also take advantage of the natural emulsifying power of cooked whey proteins. The whey's already there, and you're already cooking the mix, so why not take advantage? Generally, the emulsifying and stabilizing power of these proteins will be enough to supplement the more conventional ingredients, rather than replace them.

It may be possible to replace the conventional ingredients entirely, although there's only one reason to do so: “label friendliness.” For retail ice cream, the ingredient list has become a marketing document, and therefore a place to play to the whims of an often-uneducated public.

As long as people believe locust bean gum is somehow less natural or less desirable than tapioca starch—even though it’s a superior ingredient—manufacturers will feel pressure to use it. Or to use nothing at all. Denaturing the whey proteins provides a way—even if somewhate ironic and cynical—to use science in the service of pretending your ice cream is as science-free as Grandpa’s. 

Never mind that Grandpa’s ice cream was never all that good. The idea of Grandpa’s ice cream, in all its nostalgic splendor and purity, has created a standard everyone with a retail label aspires to. 

If you’re making ice cream at home or in a pastry kitchen, you’re lucky. You can use the ingredients that make the best product, without concern for labels and mythology. For you, getting some emulsion and texture control from the whey proteins isn’t mandatory—it’s just the cherry on top.


Next Post: Booze!



1Eventually, milk will separate. Fresh from the cow it will separate over time just from gravity (fat is lighter than water) or faster if put in a centrifuge (the way dairies separate cream from skim milk today). Emulsifiers make an emulsion relatively stable, but not perfectly so. We can add stability by thickening the water portion of the emulsion (we call anything that does this a stabilizer) or by breaking the fat globules up into a greater number of smaller ones. This physical process is called homogenization. Most of the milk we buy has been run through a high-pressure homogenizer, which blasts the fat globules into a bajillion nano-sized ones—they’re so minute and plentiful that the emulsion stays stable almost indefinitely.

2Full coalescence would mean whipping the cream into butter, which we’re not trying to do.

3Ice Cream By Robert T. Marshall, H. Douglas Goff, Richard W Hartel, p.85


For further reading:

Oil-in-Water Emulsions Stabilized by Whey Protein—Effects of Heat Treatment and High Pressure Homogenization
Instability and Partial Coalescence in Whippable Dairy Emulsions (abstract)
Studies on heat-induced interactions and gelation of whey proteins
The Effects of Polysorbate 80 on the Fat Emulsion in Ice Cream
Hydrocolloids as Emulsifiers and Emulsion Stabilizers
Ice Cream. Robert T. Marshall, H. Douglas Goff, Richard W Hartel
Emulsifiers in Food Technology Robert J. Whitehurst.
The Science of Ice Cream. Chris Clark




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

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, cooking temperature, and cooking time. 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 concentration, cooking temperature, and 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, have been used in ice creams for a long time. 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. Starches generally give better flavor release than custard, but not as good 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 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.

Semi-Stabilizers. I made up this category to include dry milk powder and invert syrup. These are both ingredients we use for other purposes, but since they thicken the free portion of water, slowing ice crystal growth and improving texture, I’m including them. Invert syrup is a solution and not a hydrocolloid. Dry milk powder is technically a hydrocolloid, but has only a fraction of the thickening power offered by the others mentioned here.

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. 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  (0.7% 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 soy lambda 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.


Next post: some equally breezy gossip about emulsifiers.


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

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 is a bad idea. Alcohol depresses the freezing point, but does nothing positive for texture. In fact, 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: too damn sweet. 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 very 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,” the idea was outrageous. And the flavor: let’s just say that I took a bite and sat there, very quietly, for a long time. The flavors 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 three main sugars we care 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 Sugars

Honey is a useful sugar in some ice cream flavors. It behaves mostly like invert syrup (because it IS mostly invert syrup), 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 45% 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.

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 convert into much larger, more complex, and more flavorful molecules. 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, and it contains water. It's not easy to know 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
30g 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.
-briefly blend again

-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. 

-add cream and vanilla extract. blend another 15 seconds on high speed.
-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.





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