How to use stabilizers in ice cream
Stabilizers are probably the most controversial area of ice cream science. They're denounced by traditionalists who think everything should be “natural”. And lauded by molecular gastronomers that think science solves everything.
They're a complicated subject. But there's nothing to be scared of here. Most of them are natural. When you use them correctly they'll almost certain improve your ice cream. And in fact, if you've made ice cream then you've almost certainly used them in some form already.
So what are stabilizers?
Put simply: stabilizers are ingredients that thicken water. This is also called adding “viscosity”. The more viscous a liquid is, the “thicker” it is.
In scientific terms, they're hydrocolloids. When hydrocolloids disperse in a liquid they bind to the water molecules, so reducing their movement. This reduced movement appears to us as increased viscosity or thickening.
The most obvious example of using a stabilizer in cooking is when you thicken gravy with flour.
Most stabilizers are natural in origin. They generally come from plant, animal or bacterial origins. However under European Law they are considered food additives and must be represented by E numbers in ingredient lists.
Why do we use stabilizers in ice cream?
Stabilizers can improve ice cream in several significant ways:
- reduce ice crystal growth
- reduce air bubble size
- slowdown melting
- increase smoothness, body and creaminess
- deliver flavour cleanly
Let's have a look at each of these contributions in turn...
How do stabilizers reduce ice crystal size in ice cream?
First of all, why do we want to reduce ice crystal growth in our ice cream? Well, ice crystals are an important part of ice cream. But if the crystals get too big, they are detectable by the tongue and give the ice cream a coarse, grainy texture.
Ice crystals are formed only during the initial freezing and churning stage in the ice cream maker.
When the ice cream is subsequently stored in a freezer, the existing ice crystals may get bigger, but no new ones are formed.
But ice crystals can grow when there are temperature fluctuations that cause existing crystals to melt and then re-freeze. Because when they re-freeze, rather than creating new crystals, the water migrates to join existing crystals, so increasing their size.
Such temperature fluctuations can actually occur both during the batch freezing process (in the ice cream maker) and during storage (in the freezer).
Ice crystal growth in the ice cream maker
During batch freezing, ice crystals are initially formed against the super cooled sides of the ice cream machine. The rotating dasher then scrapes them from the sides and moves them into the center of the mix where temperatures are warmer and where they may melt and then re-freeze later as the temperature of the whole mix decreases.
Ice crystal growth in the freezer
During storage there are many situations that could cause these temperature fluctuations. For example when the freezer door is opened and then closed. Or if the ice cream is taken out to soften before serving and then replaced in the freezer.
So the challenge for all ice cream makers, is to try to make the ice crystals as small as possible during the freezing and churning stage and to stop them getting bigger while the ice cream is being stored.
While there's plenty of material that suggests stabilizers only restrict ice crystal growth during storage, there are other studies that show that the initial size of the ice crystals formed during batch freezing are smaller in mixes that use stabilizers.
How do they do this? The science around this is not clear. But it seems likely that by restricting the free movement of water, stabilizers prevent melted ice crystals from finding and joining existing ice crystals when they re-freeze.
How do stabilizers reduce air bubble size in ice cream?
Why do we want small air bubbles in ice cream? Because lots of small air bubbles make the ice cream smoother.
How do stabilizers keep the air bubbles in ice cream small? Again, the science is not totally clear here. We know that stabilizers make base mixes more viscous. And more viscous base mixes produce smaller air bubbles.
But why do viscous mixes produce smaller bubbles? One theory is that the greater shear stress that's applied to more viscous liquids when they are being churned in the ice cream maker reduces the size of the bubbles more.
Just like ice crystals, air bubbles can grow in size and reduce in number during storage. This happens in two ways:
- Disproportionation occurs when air transfers from smaller to larger bubbles.
- Coalescence happens when two bubbles come into contact and join.
The increased viscosity that stabilizers produce also protects against these processes by thickening the films around the air bubbles and keeping neighbouring bubbles away from each other.
How do stabilizers slow down melting?
Ice cream that melts too quickly is no fun to eat! Stabilizers can help here too by both slowing the rate at which ice cream melts and maintaining it's shape better as it does melt.
This is partly due to the water binding qualities of stabilizers. Viscous mixtures simply melt slower.
But it's also due to the smaller air bubbles. Ice cream with many small air bubbles melts significantly slower and retains it's shape better that ice cream with fewer, larger bubbles. And we already know that stabilizers promote smaller bubbles!
How do stabilizers increase smoothness, body and creaminess?
So we've seen that by reducing the size of the ice crystals and the air bubbles in ice cream, stabilizers make smoother ice cream and slow meltdown.
But they also add body, produce a creamy mouth-feel and a silky finish. These qualities are largely a result of the added viscosity that stabilizers produce.
Less free flowing water produces a more solid, ice cream that tastes creamier and silkier because it's less watery.
Why are people suspicious of stabilizers?
Despite the benefits of stabilizers, many people are suspicious of or outright hostile to their use in ice cream. I think there are two main reasons for this...
- bad experiences of over stabilized ice creams
- the strange names, E numbers, and their chemically appearance make them seem "unnatural"
Over stabilized ice creams are horrible. They may have a gummy or excessively chewy texture. They can exhibit extremely unnatural melting (they don't seem to actually melt!). And they often leave a pasty after-taste in your mouth.
But this is stabilizers used badly. When stabilizers are used well, you don't even realize they're being used at all. You're just amazed by how good the ice cream is!
However, the very idea of using stabilizers is too much for some people. This tends to be down to the idea that they are somehow unnatural, that they're chemicals added to reduce costs rather than improve quality, and that they're unhealthy or even unsafe.
But as I mention above, most of stabilizers come from natural sources. And most of them have been used in cooking for hundreds of years.
It's true, they are often used in cheap, commercial ice creams to cut corners and save money. But it's all a matter of intent. If people are using them to save money we should be wary. If they're using them to make better ice cream then we should be curious.
Besides, if you've already made ice cream at home, you've probably already used stabilizers.
Stabilizers you're already using
Yep, egg yolks act as a stabilizer. So if you're making egg custard bases, you're already stabilizing your ice cream. The stabilizing chemical is egg yolk is called Lecithin and even has it's own E number: E322.
Egg yolks will give your ice cream fantastic texture and body. They'll emulsify your mix. And they'll also reduce the growth of ice crystals and air bubbles.
So why not use egg yolks all the time? Well, they're good, but they're not great. They're certainly not as good at reducing ice crystal growth as other stabilizers. And over time they let water escape, which re-freezes and makes the ice cream icy.
They subdue other flavours (especially lighter flavours like herbs and water based flavours like fruit). And add their own eggy flavour, the strength of which depends on how many eggs you use and how long and how hot you cook the base for.
So yes egg yolks will stabilize your ice cream but they're not the best performing stabilizers available.
If you've ever tried to make a Sciilain Gelato then you may have used corn flour or tapioca flour. In southern Italy they don't use eggs (or much cream) in ice cream. Instead they use these starches to stabilize their milky gelatos.
Corn flour and tapioca flour work quite well as stabilizers. They don't subdue other flavours like eggs and impart much less flavour themselves.
However, I can still detect them, whether it's through a light flavour trace or a slightly pasty texture. And again, there are other stabilizers that perform better.
While you almost certainly have some experience of the thickening properties of egg yolks and corn flour, you're less likely to have used gums before. But when people talk about the stabilizers used in ice cream it's gums that people are usually thinking about.
Gums are the most powerful, flexible and most useful stabilizers that are available to us. They suppress the growth of ice crystals better than any other ingredient. They can be used to alter the texture of ice cream in many different ways. They don't suppress other flavours and are almost flavourless themselves.
What's more, they are so powerful that we only need to use them in tiny amounts. Typically gum stabilizers would only make up 0.1 – 0.5 % of the base mix!
Most gums appear as off white powders. In fact, they're all just complex sugars, also known as polysaccharides. And they're almost all derived from natural products.
Different gums have subtlety different chemical structures that will have very different effects on the texture, body and sensory qualities of ice cream. And even used alone they are very useful.
However, if you combine one or more gums together, the effects of each can be amplified. Or nullified. Or you might get a whole new set of effects! So it is worth experimenting with different combinations of gums to see what effects you find pleasing.
Thickeners vs Gels
While all gums will thicken a liquid, some of them also form gels. Gel are substances that exhibit the characteristics of both a liquid and a solid. Food technologists define a gel as a high moisture food that more or less retains it's shape when released from it's container. And that definition's good enough for us here!
While some gums always form gels, some will only form gels in dairy based mixtures. And others will form gels only when mixed with other gums!
And different gels have different characteristics. For example they might be strong or weak, brittle or elastic etc.
When we're making ice cream, gels are generally harder to work with than mixes that are simply viscous. They can be difficult to get in the ice cream maker cleanly, so you often have to attack them with a blender them to break up the gel.
However, if you're making low fat ice creams or sorbets they're really useful because they add a creamy texture and substantial body that you wouldn't get otherwise.
Gums that form gels by themselves
Locust bean gum
Soft, elastic gel with dairy
Stiff, brittle gel with dairy
Rigid, brittle gel with dairy
Brittle, slightly sticky gel
Gums that form gels with other gums
Locust bean gum + Xantham gum
Locus bean gum + Kappa Carrageenan
Carboxymethyl cellulose + Guar gum
Carboxymethyl cellulose + All Carrageenans
Plant based gums
Most of the gums we use in ice cream are derived from plants. What sorts of plant? Well, generally they're extracted from seeds or seaweeds!
Locust bean gum (E410)
Locust bean gum (LBG), is also known as Carob Bean Flour and is made from the seeds of the Carob Tree. This tree is very common in Mediterranean countries and LBG has been used as a thickener in cooking for thousands of years.
LBG is a very popular stabilizer in ice cream. It has one of the best ice crystal size reducing powers of all the gums. And it produces, a smooth texture, a creamy mouth-feel and a silky finish. It also works well with other gums, especially Guar and Carrageenan.
The great thing about ice creams stabilized with LBG is that usually they don't seem like they've been stabilized at all. It gives ice cream a very natural feel. This is because although it forms a weak gel when frozen, that gel disappears when the ice cream melts.
However, LBG is not without it's disadvantages. It needs to be heated to fully hydrate and different types of LBG hydrate at different temperatures. But it's typically around 185°F (85°C), which is higher than ideal when making ice cream.
Used alone it can also cause wheying off, which is when milk proteins come out of solution to form crystals that are detectable by the tongue and give the ice cream a grainy texture.
Guar gum (E412)
Guar gum is also derived from a seed, in this case the seeds of the guar plant which is a legume, like a bean. Guar beans have been eaten in India for thousands of years but guar gum has only been used as a stabilizer since the 1950's.
Guar gum doesn't reduce ice crystal size as well as LBG, but it adds much more viscosity to the mix which gives more body to the final ice cream. Unlike LBG, it also hydrates at low temperatures.
But Guar works well with LBG, with each amplifying the powers of the other. So they are often used in combination.
Used in high quantities, Guar can give ice cream a chewy texture like toffee, which may be desirable or not depending on how you like your ice cream!
Carrageenans are extracted from seaweeds. Originally these were Irish Moss seaweeds and carrageenans have been used as thickeners in Irish cooking for centuries.
However, nowadays they're extracted from other types of red seaweeds that are grown in the Philippines, Tanzania and Indonesia.
Carrageenans perform pretty averagely at reducing the size of ice crystals. But they have a strong effect on texture, producing a rich and creamy mouth-feel that's similar to egg custard ice creams.
They also help prevent wheying-off (see above) so are often used in conjunction with LBG which can cause this defect.
There are three different types of Carrageenans that are used in cooking, each of which varies slightly in their molecular structure:
Iota and Kappa Carrageenans form gels with milk so are more commonly used in sorbets and low fat ice creams. While Lambada is used in ice creams with sufficient fat to stabilize without gelling.
Sodium Alginate (E412)
Sodium Alginate is also extracted from seaweed, this time the brown ocean kelp that's found in cold water areas.
It dissolves in cold water but hydrates best at temperatures between 155 and 160°F (68 - 71°C). It's pretty good at keeping ice crystals small. Add contributes a texture and body to ice cream that other gums can't replicate.
Sodium Alginate forms a gel with milk, so it's popular in low fat ice creams. And it's the way in which the rigid gel breaks into a fluid gel when it's being churned that gives the finished ice cream it's unique sensory qualities.
Carboxymethyl cellulose (E466)
Carboxymethyl cellulose (CMC) is also know as cellulose gum and is synthesized from plant cellulose.
It's probably better at suppressing the growth of ice crystals than LBG. It adds body and chewiness to ice cream to the same degree as Guar. But it forms a gel when combined with LBG, Guar and Carrageenans, which may or may not be desirable.
Since Carboxymethyl cellulose is a synthesised product that is extracted from cotton and wood pulp it pushes the boundaries of what many people would call “natural”. However it's perfectly safe and is commonly used in ice cream production.
Xantham gum (E415)
Xantham gum is a product of fermentation and is created when the bacteria Xanthomonas campestris feeds on sugar. This might sound weird. But it's just like yeast in beer!
It's an extremely versatile stabilizer. It dissolves in (and thickens) hot or cold water. Viscosity doesn't vary with temperature. It's highly resistant to freeze/thaw cyles. It works at a wide range of acidities. And it works well with other gums.
It's not the best gum at suppressing ice crystal growth. But it's really easy to get hold of in health food stores (because vegans use it as an egg substitute). And it's ready availability, it's ease of use and it's versatility make it a great gum to experiment with.
Gelatin is derived from animal collagen, usually pork or beef. And this is what they used to stabilize ice cream in the old days.
It suppresses ice crystal growth really well and gives ice cream a very pleasing smooth texture. It's also very easy to get hold of.
However, it has largely fallen out of favour, because it's expensive and because it's an animal product.
Pectin is extracted form citrus feel and apple pomace. Pectin has been used for many years as the gelling agent in jam.
There are two types: “low methoxy”, which requires calcium to gel and “high methoxy” which will gel at low pH with loads of sugar.
Denatured Whey Proteins
When we heat the ice cream mix, some of the whey proteins in the milk undergo partial unfolding and begin to form a network similar to those formed by hydrocolloids. This process in called “denaturing” and will help stabilize the ice cream in a similar way too.
However, the stabilization is not nearly as powerful as the hydrocolloid's and should be seen as an addition to rather than instead of.
How to use stabilizers
So if you're thinking you might like to experiment with stabilizers (and specifically gums) there are three steps that you need to get right:
Gums are so powerful you only need to use a tiny amount. Typically they make up between 0.1 and 0.5% of the weight of the base mixture. And if you go just slightly above these proportions you'll start to get over stabilized ice cream which can be quite unpleasant.
So in order to get your weight measurements right you'll need some scales that are accurate to 0.01g. You might be able to get away with experimenting with ¼ teaspoon measures, but it'll be hit and miss. And good quality scales aren't expensive.
Once you've accurately measured out your stabilizer, you need to mix it with the rest of the ingredients. Gums tend to clump together and won't disperse properly if you just dump them into a liquid. And if they're not dispersed, they don't work!
The best way to get an even dispersion is to add the stabilizer to all the other dry ingredients and then mix them thoroughly with a fork or a whisk. Spend a good 5 minutes on this to make sure it's properly mixed.
Once it is mixed, add the liquid and give it a proper going over with a hand blender. Again spend a good few minutes on this.
Some people suggest using the blender to form a vortex in the centre of the liquid and then pouring the dry ingredients into the middle of the vortex for the best dispersion. I haven't found this necessary but it might help.
But I can't stress the importance of this step enough. If you don't disperse the stabilizer it will clump together and won't fully hydrate. Which means your mix won't thicken properly. And your ice cream will be poorer.
In order to be effective, a stabilizer must be hydrated: it must absorb water. Some need to be heated, others hydrate in cold water. Some stabilizers hydrate faster than others. You need to know how to get the best hydration from the stabilizer you're using.
For example, Locust Bean Gum needs to be heated to about 185°F (85°C). While Guar and Xantham gum hydrate at room temperature. And Guar needs up to an hour to fully hydrate. But Xantham gum hydrates much quicker.
Measuring, Dispersion and Hydration: A summary
So remember. Make sure you're working with the right amount of stabilizer by weighing it accurately. Properly disperse it by mixing it thoroughly with the other dry ingredients before you add liquid. And treat it with the appropriate amount of heat and time to fully hydrate it. Get these three steps right and you should have great success!
Stabilizers are often treated with great suspicion and even hostility. Generally, I think this is because people are ignorant of what they are and why we might want to use them.
They're natural and they're safe. Of course some people may be allergic to them. Just as some people are allergic to eggs. If that's the case, they should be avoided.
However, they can help us make much, much better ice cream. And that's the most important point here. We're not using them to save money. We're not using them to cut corners.
When we use them, we use them to deliver better texture, better body, a more creamy, luxurious finish. And more stability!
As home-made ice cream enthusiasts we're already hampered by shitty machines that take ages to freeze our mixtures and inflexible freezers that are never at the right temperature.
Stabilizers can help us overcome these disadvantages to make ice creams that rival the professionals. I urge you to at least experiment!