Emulsifiers are used as a key ingredient in ice cream. As a food additive, they hold several functions, depending on the food. Generally, they help increase food palatability, increase food volume and aeration, decrease stickiness, improve food flavor, enhance food textural properties, and impart foam stability.

In ice cream, emulsifiers helps the ice whip more readily. The ice cream also becomes dryer, has better melting resistance, is smoother, and has a better texture. In some ice cream, emulsifiers also destabilize the milk protein in the final ice cream product to improve its structure. Because of their relatively higher surface activity and ability to form liquid crystal metaphases, emulsifiers in ice creams tend to promote protein desorption from the surface of fat droplets. Emulsifiers serve as nucleation sites for triglyceride surface crystallization. They also aid in the formation and stabilization of ice cream foam prior to partial fat globule coalescence and freezing.

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Traditional emulsifiers for ice cream production include egg yolks. They contain lecithin, a natural emulsifier that aids in uniting the molecules of fat and water to produce a creamy and smooth texture. Egg yolks are a common ingredient in custard-based recipes because they give ice cream a richness and depth of flavor.

Today, there are many emulsifiers that can be used for ice cream making. Aside from lecithin from egg yolks, mono-/diglycerides, and polysorbates are commonly used. These emulsifiers are often used as blends.

Let’s discuss them briefly.

HOW EMULSIFIERS WORK IN ICE CREAM

Emulsifiers have a unique chemistry. They have molecules with two ends, one of which is drawn to water and the other to fat. The water-loving end of an emulsifier’s molecule surrounds the water droplets in an ice cream mixture, while the molecule’s fat-loving end surrounds the fat droplets. Small emulsion droplets are produced as a result, which the emulsifiers stabilize and disperse throughout the mixture.

The emulsified fat droplets are broken down into smaller pieces as the ice cream mixture is frozen and churned, giving it a smooth and creamy texture. Without emulsifiers, the ice cream’s fat would collect into lumps, giving it a grainy or lumpy texture. Additionally, emulsifiers aid in preventing the growth of large ice crystals, which can cause the ice cream to separate.

In order for emulsifiers to function properly, the aging must be adequate. During this stage of production, emulsifiers adsorb to the surface of the fat droplets, and partially replace the milk proteins. The emulsifiers start to crystallize as the mix cools. This makes them more hydrophobic. Thus, they adsorb more onto the fat droplets. When the ice cream mix is frozen, it is challenging to incorporate and stabilize air bubbles without them. This is especially true in the industrial setting. The nature of the mix and the intended use determine the aging time, which in turn determines the degree of fat crystallization and emulsifier adsorption.

Aging of mixtures of extruded products for at least 6 hours causes greater partial coalescence. This usually results in a stiffer ice cream. For most types of ice cream products, two hours of aging is sufficient. In factories, it is convenient to age a mixture over night and store it in aging tanks prior to production. Ideally, it should not be kept for more than three days.

EGG YOLK

Egg yolk contains several components that make it a great functional ingredient in food manufacturing.

But in ice cream making, lecithin is the most important as it contributes the most to egg yolk’s emulsifying abilities. The approximate weight percentages of the components of an egg yolk are: 50% water, 16% protein, 9% lecithin, 23% other fat, 0.3% carbohydrate, and 1.7% minerals. Lecithin is made up of phospholipids and phosphatides. It is frequently utilized in premium, homemade, or “all-natural” ice creams

Lecithin does its job by combining the molecules of fat and water to produce a creamy, smooth texture. Without it, ice cream mix can become icy or grainy. Additionally, lecithin aids in stabilizing the ice cream, preventing it from melting too quickly or freezing up too hard. It can aid in lowering overrun (the amount of air whipped and incorporated into the ice cream) of the product.

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Egg yolk is typically supplied for use in the production of ice cream in one of three forms: pasteurized fresh egg yolk, frozen pasteurized sugared egg yolk, or dehydrated egg yolk. Normal usage levels of egg yolk solids range from 0.5% to 3%. Frozen pasteurized sugared egg yolk often contains 10% sucrose to prevent damage during freezing. Super-premium ice cream products may contain high concentration to give ice cream an eggy flavor.

MONO-/DIGLYCERIDES

Mono- and diglycerides are emulsifiers that are made up of a glycerol molecule and one or two fatty acid molecules attached to it. Mono- and diglycerides are lipids or fats that are soluble in both fat and water. This unique property enables them to function as emulsifiers, assisting in the combination and stabilization of fat and water-based ingredients in food products such as ice cream.

Due to the hydrophilic nature of the glycerol end and the hydrophobic nature of the fatty acid end, mono- and diglycerides are surface active. The fatty acids in mono- and diglycerides determine their characteristics, just like they do for triglycerides. Vegetable fats like soybean oil and palm oil that have undergone partial hydrolysis are used to create mono- and diglycerides. They typically contain diglyceride, a small amount of triglyceride, and monoglyceride in amounts ranging from 40% to 60%.

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Ice cream production frequently uses fully saturated mono-/diglycerides that primarily contain stearic and palmitic acids. An example of this is glycerol monostearate, which typically makes up about 0.3% of the ice cream mix. This is ideal for low fat ice cream since it provides smooth texture and body similar to regular ice cream.

POLYSORBATES

As opposed to mono- and diglycerides, polysorbate types of emulsifiers are known to be more effective at displacing proteins from the oil-water interface, making them better emulsifiers for ice cream. However, the mono- and diglycerides have better foaming properties, which means they can create more initial foam before the fat droplets clump together at the air-water interface.

Monoglycerides and sorbitan esters of fatty acids share structural similarities. Polyoxyethylene sorbitan monooleate, commonly called polysorbate 80, is present in many products in a reasonable amount, keeping the ice cream scoopable. Instead of glycerol, polysorbate 80 has a fatty acid attached to a sorbitol molecule. The sorbitol molecule also has polyoxyethylene groups attached to it, making it water soluble. When used as an ice cream emulsifier, polysorbate 80 can be used at concentrations of 0.02% to 0.04%. Like most food additives, polysorbates are safe to consume in moderation, and are subject to regulation by food safety authorities.

References:

M. Wallert, K. Colabroy, B. Kelly, J. Provost (2016). The Science of Cooking: Understanding The Biology And Chemistry Behind Food And Cooking. John Wiley & Sons, Inc..

Chris Clarke (2004). The Science of Ice Cream: RSC (2nd edition). RSC Publishing.

P. Cheung, B. Mehta (2015). Handbook of Food Chemistry. Springer

T. Msagati (2013). Chemistry of Food Additives and Preservatives. John Wiley & Sons, Ltd.

The post Emulsifiers Used In Ice Cream appeared first on The Food Untold.

Here is one thing that is so true—everybody loves desserts. And top of everybody’s list is ice cream. According to World Atlas, New Zealand consumes the most ice cream per capita at 28.4 annually, the United States comes in second at 20.8, and Australia at 18.0. We can’t blame them, though. Who can’t resist that sweet, creamy frozen dessert? The reason for the desirable characteristics of ice cream lies beyond how it is made.

There are several different kinds of edible ice, which are simply blends of water, sugar, flavorings, and additional ingredients that are partially frozen then beaten to create a stiff foam. In most types, milk or cream is a key component. Many types of ice cream contain dairy products such as cream, skim milk, sweet cream buttermilk, or sweetened condensed milk, as well as optional caseinates.

Let’s take a look closer at how ice cream is made through science.

ICE CREAM IS MADE UP OF A MIXTURE OF SOLID, LIQUID, AND GAS

For the many of us, ice cream is merely a frozen bowl of cream. But no, ice cream is one of the many examples of emulsions. Emulsions are mixtures of liquids that do not normally mix, oil and water for example. (We will talk about emulsifiers in ice cream further in this blog post.) Instead, the liquid gets dispersed throughout the other liquid. In the case of ice cream, the mixture is made up of three phases: partially frozen milk fat and ice (solid); unfrozen cream and water (liquid); and trapped pockets of air (gas).

Milk fat and ice

The frozen fat globules and ice water are the solid ingredients in ice cream. They are dispersed throughout the liquid phase of sugar water and cream. These components are typically unstable. But the application of emulsifier prevents them from collapsing into solid and liquid phases.

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Fat contributes to flavor by giving the tongue a creamy sensation and sweetness. Additionally, they are partly responsible for the freezing-point depression and the increase in viscosity. The protein is important for the creation of fat-globule membranes during homogenization and partially assists in stabilizing the foam lamellae during air incorporation. Low temperatures can cause lactose to crystallize.

Ice crystals are essential for the right consistency and coolness in the mouth. Moreover, the low temperature causes the sweetness to be less intense. Small crystals should form in order to avoid sandiness. The quicker the freezing, the smaller the crystals. Cooling should occur quickly to prevent temperature swings and large crystal formation.

To reduce the price of ingredients, whey components are frequently used to replace a portion of milk solids that are not fat. In some countries, vegetable fats, including palm kernel oil that has partially undergone hydrogenation, are frequently used in place of milk fat.

Air

Air makes up a significant portion of ice cream, making this dessert a foam as well. In fact, air makes up up to 50% of the final volume! Ice creams are sold by volume though. But if you try weighing a liter of ice cream, you would probably get only about 500 grams. But the thing is that air contributes to what makes ice cream desirable—light, soft, and fluffy.

In commercial ice cream making, overrun refers to the increase of volume due to incorporation of air in the mixture during freezing. Typically, ice cream overrun range between 60 to over 100%. 100% overrun means half of the ice cream’s volume is air. To make ice cream more affordable, manufacturers tend to exceed 100% overrun. One downside of this is that ice cream melts more readily. Overrun can be calculated by the following formula:

Ice cream can be found in a bewildering array of grades and styles. The best ingredients are used in superpremium and premium ice cream, which has a low overrun and a high fat content. Gelato resembles frozen ice cream but has more fat and little to no overrun. Soft serve ice cream has up to 60% air overrun and is low in fat (3 to 6%). Compared to superpremium or premium ice cream, standard ice cream contains more overrun (air).

EMULSIER IS A KEY INGREDIENT

We have already learned that ice cream is not a solid frozen foam. Instead, it is a mixture of three phases of solid, liquid and gas.

These three phases mix with one another to create a colloid. A colloid is a mixture with characteristics of both homogeneous and heterogeneous mixtures. A closer look at it, it is a microscopically dispersed mixture in which dispersed particles do not settle out. In the case of ice cream, it is both an emulsion and a foam, both of which can be described as a colloid.

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The solid phase of frozen fat globules and ice water spread across the liquid phase of sugar water and cream in ice cream is normally unstable. If kept that way, the mixture will only separate into two phases of fat and water. To prevent this from happening, ice manufacturers use emulsifiers. Emulsifiers are the additives or agents that act as a bridge between the phases of fat and water. Ice cream has a variety of various stabilizers and emulsifiers.

The mouthfeel and creaminess of the ice cream depend heavily on the ratio of each colloid phase. If there is too much fat, the ice cream will have the consistency of butter; if there is too much sugar or milk solids, the ice cream will be weak; and if there are too few crystals, the ice cream will not get crunchy.

Here are some examples of emulsifiers in ice cream.

The majority of ice creams contain stabilizing emulsifiers to reduce the growth of fat and ice crystals, which lessen the flavor of ice cream.

Alginate is a frequently used to lessen the production of ice crystals. It is sourced out of the cell walls of algae. Alginate has a lot of —OH functional groups and can easily form hydrogen bonds with water to bind it. Alginate’s significant hydrogen bonding restricts water movement and creates a gel that serves as a thickener.

The structure of the water-carbohydrate complex also prevents ice crystals from forming. Many foods substitute carrageenan, a cell wall carbohydrate from red algae (seaweed), with alginate.

Polysorbate 80 is another typical ice cream emulsifier. This complex carbohydrate is attached to a long unsaturated fatty acid. It is used in ice cream at fairly high concentrations to keep the ice cream scoopable. While the fatty acid tail of Polysorbate 80 binds hydrophobically with the fat globules, the carbohydrate component of the molecule interacts with water and protein. The water and fat phases are kept together by this covering. This post discusses emulsifiers in ice cream in more detail.

ICE CREAM MANUFACTURING

Now that we have discussed the science of ingredients in making ice cream, let’s discuss the manufacturing process.

The first stage of the manufacture is composing the ice cream mix. The additives include emulsifier, stabilizer, and flavor and color substances. Then, the mix is subjected to pasteurization, homogenization, cooling and holding (for aging), and quick freezing.

Pasteurization

With the ingredients prepared, they are pasteurized. Pasteurization minimizes the risk of disease and extends the shelf life of milk. It is a mild heat treatment (176°F for 25 seconds for ice cream) of a product for it to be safe for human consumption. It achieves its objective by primarily killing pathogenic and spoilage microorganisms.

Since lipase (fat) is still somewhat active even at very low temperatures, inactivating it is the second key goal of the process. Therefore, bacterial lipases ought to be avoided. Lipase is an enzyme, or a special protein that speeds up the rate of many reactions. This naturally occurring enzyme in milk produces flavor molecules that are desirable in cheese making, but only produce rancidity (oxidation of oils or fats in food science) in ice cream making.

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Finally, pasteurization makes the mix more desirable, especially for hardened ice cream, because it decreases the product’s susceptibility to autooxidation. Food products that have undergone autooxidation lose their nutritious value and develop distinctively unpleasant and off flavors.

Homogenization

Homogenization’s main purpose is to stop creaming, or the rise of fat to the top of the milk container. In the case of ice cream, the process aims to provide the ice cream mix a sufficiently fine, smooth texture and slow melting properties. This is achieved by shrinking the size of the fat globules to create a stable emulsion of the fat. Hence, homogenization is a must for ice cream that contains fat.

The mixture should homogenize at the pasteurizing temperature. At any given pressure, the elevated temperature results in more effective breaking up of the fat globules, and also lessens fat clumping. However, the excessive formation of homogenization clusters should be prevented. This will only make the ice cream mix excessively viscous and the desirable fine texture will not form.

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Several factors affect the effectiveness of homogenization. The homogenization pressure should be adjusted based on the amount of fat, the level of pasteurization, and, if necessary, the mix’s additional composition. For example, the pressure for high-fat ice cream should be low. Reduced pressure lessens the chance of cluster formation, especially for ice cream mixes with more than 15% fat. High pressure during homogenization produces a more stable emulsion as well as smaller fat globules, which is ideal for low-fat ice cream.

Cooling and ripening

Storing ice cream at a low temperature for some time is for two reasons. Before the ice cream mix goes into the freezer, the majority of the fat in the fat globules should have crystallized. This is where cooling at 39.2°F (4° C) does its job. It is important to note that due to the small size of the fat globules, there may be significant undercooling. Another reason for ripening at low temperature is that some emulsifiers require considerable time at low temperature to displace protein from the fat globules. Furthermore, some stabilizers, such gelatin and locust bean gum, take a long time to swell after being dispersed.

Freezing

This is quick freezing. Slow freezing creates larger ice crystals, and that is not ideal. As air is beaten in, ice is created. This has to occur concurrently. After most of the water is frozen, any beating in of air becomes harder to achieve. After the air has been beaten in, the foam structure can be damaged by freezing because it causes insufficient churning of the fat globules. Additionally, the strong beating promotes quick chilling, which allows for the formation of tiny ice crystals.

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In constantly operating machinery, mix and air are introduced into the equipment in specified volume quantities. This allows the overrun to be precisely regulated, while a stirrer shrinks the air cells. The manufacturing procedure takes a short amount of time. At 38.3°F (3.5°C) to 44.6°F (7°C), the ice cream mixture comes out of the freezer.

References:

V. Vaclavik, E. Christian (2014). Essentials of Food Science (4th edition). Springer.

M. Wallert, K. Colabroy, B. Kelly, J. Provost (2016). The Science of Cooking: Understanding The Biology And Chemistry Behind Food And Cooking. John Wiley & Sons, Inc..

Pieter Walstra, J. Wouters, T. Geurts (2005). Dairy Science and Technology (2nd edition). CRC Press.

T. Britz, R. Robinson (2008). Advance Dairy Science and Technology. Blackwell Publishing.

The post The Science Of Making Ice Cream appeared first on The Food Untold.

I live in a tropical country. So it makes perfect sense that ice cream is an everyday food for us, especially for children. A common scenario here is an ice cream vendor peddling his product on a hot afternoon. When I was younger, I used to wonder why they immerse ice cream tubs in ice and salt bath before they head out. But I never got the chance to ask them why. Does it enhance the flavor? Does it make the ice cream more resistant to melting? It turned out that ice cream makers have been using salt and ice bath in making their product since the early 19th century. They do this to actually make ice cream freeze faster. But how does it work?

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Because as far as I know, countries away from the equator use salt to melt ice. When it snows, people would spread salt on roadways to prevent the snow from freezing, keeping the road from being icy and dangerous for travelers. This works because salt messes with the freezing point of water, impeding the ability of water to form ice crystals.

But how does salt and ice bath work the other way in making ice cream?

SALT AND ICE LOWER THE FREEZING POINT

Under normal conditions, pure water freezes at 32°F (0°C). But this temperature is not sufficient to freeze the liquid ice cream. Milk is one of the main ingredients in making ice cream. It starts to freeze at 31.1°F (0.5°C). A typical ice cream would also include ingredients such as sugar, color, and flavor. For this reason, a temperature colder than ice is necessary to freeze the ice cream. Generally, ice cream freezes at -15°F (5°C) or lower. But with enough salt (sodium chloride) and ice, temperatures of -4°F (-20°C) can be reached, helping the ice cream to freeze faster.

The combination of salt and ice do not melt the salt though. Instead, these two lower or depress the melting point of the ice water—a colligative property. In chemistry, a colligative property is the property or characteristic of a substance that varies according to the number of particles of solute (salt in this case) in a solvent (ice or water).

This does not depend on the chemistry or the nature of the particles, just the number of particles. The more particles dissolved, the greater the impact on freezing point depression.

FREEZING POINT DEPRESSION

When we take ice out of the freezer, its temperature is roughly the same as the inside of the freezer. But as it stays out, it starts absorbing heat, raising its temperature. We all know that water freezes at -32°F (0°C). Once the ice reaches this temperature, it begins to melt. But in the presence of salt, its melting point can be lower than 32°F. Hence, a salt and ice water bath can stay liquid even at a temperature below 32°F—this phenomenon called freezing point depression can help freeze our ice cream before the ice melts completely.

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Salts are ionic molecules—the bonds have electric charges. The chloride ions are negatively charged, whereas the sodium ion is positively charged. These are opposite charges that attract one another. However, the ionic bond breaks in water because the ions is solvated by water molecules. Sodium chloride dissolves into sodium cation and chloride anion. For each molecule of NaCl in water, the sodium and chloride particles are able to impact the freezing point depression.

The freezing point depression can be measured by the below formula.

Based on the formula above, we can see that more particles means a higher total concentration and more effect in the freezing point. But only impurities such as salt have the capability to do this. When dissolved in water, sugars such as lactose and sucrose do not dissociate into ions. Therefore, one molecule of NaCl has twice the effect on the freezing point than does sucrose.

MAKING ICE CREAM AT HOME

Want to see how freezing point depression works at home? Sure, you can by freezing ice cream without using your home freezer! You will only need three components here: fat, water, and sugar. So ready your whipping cream (1/2 cup), sugar (1/4 cup), milk (1/2 cup), and some vanilla (1/4 teaspoon) for flavor. Place these ingredients in a mixing bowl and mix them until the sugar has dissolved. After that, pour the liquid ice cream in a medium sealable bag. Make sure to squeeze out all the air before sealing the bag. In a larger sealable bag, place crushed ice. Try to measure the temperature of the larger sealable bag. if you have a thermometer. You should get a reading of around 24.8°F (-4.0°C).

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Now add one cup of salt in the sealable bag. Bigger coarse salt crystals work better. Wait a little moment and then read the temperature again. You should get a reading much lower than that with crushed ice alone. With calcium chloride hexahydrate salt, a calcium salt, temperatures of around −40°C can be reached.

Place the sealable bag with liquid ice cream inside the bag filled with ice and salt. Now shake the bags for 10 to 15 minutes. What happens here is that the ice starts to melt as it absorbs heat from the ice cream mixture. In return, the temperature of the ice cream becomes lower.

After shaking, check the bag if the ice cream is already solid. Otherwise, refill the larger bag with crushed ice and shake the bags again for several more minutes. Remove the inner bag and enjoy your ice cream.

So that is how salt helps freeze ice cream. Want to learn more about freezing point depression? The Chemistry Library discusses freezing point depression in more detail.

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