Electron micrograph of a milk fat globule. Here’s where the action is. |
If you’re interested in making egg-free ice creams with the best possible texture, or are just a glutton for minutia, read on.
Basics
Emulsifiers in Ice Cream
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.
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.
Non-Egg Emulsifiers
Because they naturally form together, the mono- and di- versions are usually used together and packaged together. The monoglycerides, however, are thought to be the functional component. These typically make up about 40% of the blend. It’s also possibly to use monoglycerides by themselves which are usually isolated to glycerol monostearate (GMS) or occasionally glycerol monooleate. These work in much smaller quantities but are more expensive than the usual mono- / di- mixture.
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3-D diagram of a ß-Lactoglobulin whey molecule. When it denatures (cooks), it unwinds. |
Denatured Whey Proteins
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.
• fresh milk and cream that have been low-temperature pasteurized
• 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.
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.
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
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I've begun experimenting with soy lecithin for some eggless bases and ran into an issue with graininess -- I'm wondering if you have any insights that could help pinpoint the cause:
Control (A): - plain base using egg yolk as the emulsifier (~36g / 1L base)
Test (B): same base as above but substituting soy lecithin for egg yolk (3g / 1L base)
The egg yolk base came out perfectly, but unfortunately the soy lecithin base had a clotted appearance and an extremely grainy texture.
I've seen it mentioned elsewhere that graininess in recipes using lecithin could be due to insufficient shear force. But, I did homogenize the base after cooking with a vitamix for >1 min. Any other thoughts on what might cause this?
Is it possible to over-homogenize the base and cause the destabilized fat to start sticking together in the presence of lecithin?
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Would using the egg yolk powder just reintroduce the eggy flavor thus defeating the point?
Did I just answer my own question? ;)
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However, I've since used soy lecithin dozens of times without incident, so my best guess is that I over-blended my base (while measuring out ingredients for the next batch).
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Thanks!!!
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I will emailing the spreadsheet with some info to your [email protected] shortly.
Sorry for the delay in my reply!
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So, certain amount of crystallization is necessary during aging to prevent full coalescence of the fat droplets(which results in one large fat globule), but complete crystallization prevents any coalescence from taking place because of their rigidity. Because of that, we need to aging to make proper amount of crystallization.
This is what I understood. Is that right? :)
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We don't use emulsifiers to prevent fat from coalescing. The fat needs to partially coalesce in order to whip into foam. The emulsifiers we use in ice cream actually weaken the milk fat's natural emulsification, to help with this process. Counterintuitively, we use emulsifiers as de-emulsifiers.
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The fat needs to be crystalized to coalesce and whip, so you can't skip this step. Chilled mix also freezes faster, which will improve the texture.
It's less clear how long you have to chill the mix. The term "ripening" suggests that all kinds of magical stuff happens, which I've never seen any support for. Some people have said the amount of time is unimportant, as long as you chill the mix enough.
I haven't tested this, since my habit is to let it chill overnight. But that may be more time than necessary. Either way, emulsifiers don't substitute for this step.
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I was studying about how the emulsifiers work, and I concluded that it prevents fat from coalescing each other and prevents water from crystalization.
but this article, on the other hand, says that the addition of emulsifier is needed for fat to make coalescence. This means, emulsifier is needed not to emulsify fat and water in milk and to make more whip. So I got confused. Which part of my understanding is wrong?
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I am back to making ice cream as a hobby after a year off and I have started a blog mainly for beginners. Is it ok if I link this for resources? I don't want to have to go over the components of ice cream structure when you have a great series here.
FYI, if you are looking for a spreadsheet, I wrote one when I started learning how to make ice cream myself last year. It has remained WIP for the last gajillion years but it tunes sweetness, freezing point depression, solids etc and I have a table of main ingredient weights that are pulled from google, nutrition labels and USDA website mainly.
Looking forward to your next entry.
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thanks again for writing. That's an interesting problem—my first inclination is that you're right about the emulsion being destabilized too much. I don't know why this would happen with just 3g / liter lecithin. What more can you tell us about your recipe and method?
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good question. All my research is based on powdered lecithin. I haven't seen much about the liquid version, so don't for sure all the differences. I've read that the liquid version contains a higher percentage of fats, which suggests a lower percentage of pure emulsifier, so by weight you may have to use more. People find the liquid a bit easier to mix, but assuming you're using a blender this won't be an issue. I think the main concern when chosing a source of lecithin is a mild flavor and odor. A good quality product will be undetectable in ice cream.
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Should we prefer liquid lecithin or powdered?
Do you know if they have any differences in the final product?
Thanks!
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Really appreciate all the work you've put in here. Out of curiosity, have you ever given thought or experimented with whey protein isolate powder, the kind used by fitness enthusiasts, in ice cream recipes? Given that cooked proteins are the key agent, I'd be interested in if they might be a more direct route than milk or milk powder.
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Your observations about textures and skin formation in creme anglaise are interesting. I've never experimented with this. I've also never had issues with oiliness or skin formation on anglaise or custards.
The research I've seen primarily shows these ingredients as substitutes for eggs, and as whipping aids ... which I believe means that they promote more overrun and possibly a finer foam structure in high-overrun ice cream. But again I can't speak from personal experience.
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ive been doing some research on ice creams and youve given me a detailed idea on how they work, i am currently doing some research on a high protein ice cream using whey protein, from what i understand proteins act as emulsifiers, and since the fat content is low in whey the result would be an icey texture, would there be a way to still make a creamy texture using the primary ingredient as whey protein?
p.s there will be no cooking involved since itll all be powder based just add water and freeze
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as far as I know, whey develops its emulsifying ability when cooked; it needs to be partially denatured, so the molecules unfold enough to expose their active surfaces. I don't know what, if any, effect you'll get from uncooked whey. I'm curious to know what you discover. If you've been researching and experimenting with this, I'm sure you've figured out much more than I know. My approach to ice cream is quite counter to my approach to sports nutrition!
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Sucrose esters look like an interesting ingredient. I've found very little information about their behavior in ice creams. The only real drawback I can find is their price. If you experiment with this ingredient, please write back and let us know.