Emulsions: A Togetherness Not Easily Achieved

By Miranda Kohout

All pastry is mayonnaise!

There are few better ways to drive home an important concept than with a seemingly nonsensical declaration. Once you have your cooks’ or students’ attention, you can pair a silly, but hopefully memorable, phrase with solid science. Emulsions deserve all the care and attention that we, as cooks, chefs, bakers and chocolatiers, can give them, for they lie at the heart of nearly every successful product that leaves our kitchens.

What is an emulsion?

An emulsion is a combination of two liquids that cannot dissolve in each other. The scientific word for this is “immiscible.” Water and vinegar, for example, cannot be emulsified; their molecules will mix freely and with little intervention. Olive oil and cocoa butter are examples of two immiscible fats that could be emulsified, while olive and canola oils are miscible; they mix easily. Most commonly, and especially for pastry and confectionery applications, emulsions are formed between fat and water.

To speak technically about emulsions requires some specific language. When you create an emulsion, one of the two liquids will break up into tiny droplets. The liquid in these tiny droplets is referred to as the dispersion phase. The liquid in which the droplets are dispersed is the continuous phase.

Food emulsions can be either O/W or W/O, that is, Oil-in-Water or Water-in-Oil. In O/W emulsions, the oil is the dispersion phase, and the water is the continuous phase. In W/O emulsions, this is flipped: the water (dispersion phase) is dispersed in the oil (continuous phase).  Mayonnaise, milk, heavy cream and some buttercreams are common examples of O/W emulsions; butter and processed cheese are examples of a W/O emulsion.

Chocolate is not a true emulsion; it is the suspension of solids in fat. It behaves very similarly to an emulsion, and it is often beneficial to treat it as such.

What is homogenization?

A product exhibiting the qualities of a good, stable emulsion is often referred to as homogenous. While the words homogenization and emulsification are very closely linked, they are not synonymous.

Homogenization is any mechanical process – even stirring by hand – that reduces the size of fat particles, allowing for easier dispersion in a continuous phase. It is key to creating uniform and stable emulsions. The most familiar homogenized product to many of us is milk. Straight from the udder, milk will naturally separate. The fat will float on top of a mixture of water and milk solids.

For the sake of appearance, convenience, taste and shelf life, industrially processed milk is nearly always homogenized. The fat particles in the cream are reduced to an incredibly small size, so that, rather than clinging together in a mass and floating to the top, they will easily disperse in the water/solid mixture.

While an emulsion cannot be created without homogenization, and the result of homogenization is often an emulsion, the terms are not technically interchangeable from a scientific perspective. In practical conversation, however, it is perfectly acceptable to refer to an emulsified mixture as “homogenized.”

Emulsions in Pastry and Confectionery

Mayonnaise, hollandaise and vinaigrette are all excellent and common examples of emulsions that come from the savory side, but the pastry kitchen and the chocolate atelier are practically built on emulsions – possibly literally, considering that asphalt, paint and sealants are all emulsions as well.

A stable emulsion is required for the success of:

• Ganache
• Buttercream
• Cookie dough/tuiles
• Sponge batters
• Anglaise
• Caramel
• Ice cream, gelato, frozen yogurt, sherbet

Common pastry ingredients are emulsions, too. Mishandling our modern, emulsified versions of butter, milk or cream can lead to undesirable results in applications that rely heavily on them.

Emulsifiers: a little help from a friend

If you have ever made a basic vinaigrette (oil + vinegar), you know that even the most beautiful, homogeneous emulsion can be fleeting, even if you’ve combined the ingredients effectively and efficiently with a blender or burr mixer. Often, creating a lasting emulsion is impossible or at least incredibly difficult. The chemistry of the two liquids will win out, and the mixture will separate. This is where an emulsifier can help.

Let’s first look a little more closely at what is happening in an emulsion.

When two liquids can’t mix due to chemical incompatibility, they will separate. Each liquid will arrange itself to minimize contact with the other liquid. In a vinaigrette, all the vinegar will sink to the bottom, and all the oil will rise to the top. This behavior – acting to minimize surface area – is an example of surface tension.

Vigorously whisking the oil and vinegar will homogenize the oil – break it up into smaller droplets – and allow for the creation of an O/W emulsion, but this is temporary; the two liquids will separate quickly.

Enter an emulsifier. Phospholipid-type emulsifier molecules have two ends. One is fat-compatible and water-averse, and the other is water-compatible. Protein-type emulsifiers are essentially the same, but they are composed of longer chains of molecules, with a number of fat- or water-compatible sections. In our vinaigrette example, the water-loving ends of certain egg yolk or mustard molecules will dissolve in the vinegar, and the water-averse ends will join together to form a barrier around the oil droplets, effectively breaking the surface tension and allowing the oil to disperse easily in the vinegar. 

Unfortunately, our oil-and-water romance doesn’t end here. While an emulsifier can make it easier for a cook to combine two liquids, it won’t necessarily facilitate a permanent happily-ever-after-style ending, and the two liquids may still separate – the emulsion may not be stable. In kitchen-speak, we say the emulsion “broke.” In some cases, it is necessary to add large, bulky molecules to block the two liquids from coalescing and returning to their separate corners. Proteins, pectins and starches can all serve to stabilize an emulsion. In some cases, these are a standard part of the recipe; in other cases, they may need to be added.

Sources of Emulsifiers

Lecithins

Even though our spell-check doesn’t like it, we may refer to lecithins in the plural because there is more than one type of lecithin and each one has specific, though similar, properties. The most common sources of lecithin are soy, sunflower and rapeseed. All are a mixture of phospholipids.

Egg yolks

Egg yolks are an excellent and abundant source of emulsifiers, containing both emulsifying phospholipids and proteins.

Commercial stabilizer mixers for ice cream and baking

Pre-made stabilizer mixes contain ingredients to facilitate and stabilize emulsions, primarily through controlling water. Gums such as xanthan, guar and cellulose are common ingredients in ice cream stabilizers, along with gelatin, and synthetic emulsifiers such as mono- and diglycerides and polysorbate-80 are included in some mixes. In baking, starches may be part of a stabilizer, and either type of product may include lecithin.

Signs of Poor Emulsification

Ganache:

A poorly emulsified ganache can look curdled or separated. Ganache formulas that are not properly balanced or not made according to best practices can be oily or grainy; the effect can range from subtle to overtly greasy or gritty.

Sponge Batter:

A sponge with a broken batter can overflow its mold or pan in the oven and may have a heavy, greasy texture. It may stick to the mold where previous batches of the same recipe did not. Financiers are a prime example of a sponge batter that requires careful emulsification for success.

Buttercream:

Like a broken ganache, buttercream that is not properly emulsified can be greasy, gritty, curdled or separated. Icing a cake with it will be an exercise in frustration with poor, uneven results.

Cookies/Tuiles:

A greasy texture is the most notable result of a cookie dough lacking a good, stable emulsion. Tuiles are even pickier, with fat leaking from the tuile, a lacy rather than smooth texture, and a lack of crispness.

Caramel:

Problems with caramel may become apparent immediately upon adding liquid, or when the cooled caramel separates, rather than remaining smooth and homogeneous.

Frozen Desserts:

What could have been a smooth, indulgent ice cream or gelato will be grainy, icy or contain noticeable fat particles if the formula’s fat and water aren’t balanced and well emulsified.

Custards:

A classic anglaise is a great place to see emulsification at work. An anglaise that curdles or separates may not have formed a proper emulsion.

How to Create Stable Emulsions (General Best Practices)

Use a balanced recipe

No amount of mixing will fix a recipe where the balance of fat and liquid isn’t quite right. This can vary depending on the application’s intended purpose. For example, a slab ganache that will be cut and enrobed will have a different water-to-fat ratio than a ganache used to fill shells. When troubleshooting, consider all sources of fat and liquid. Remember that eggs add both fat and liquid, as does butter. While we may think of heavy cream as being high in fat, it is primarily water.

The recipe and the method should be compatible. For example, ice cream bases formulated for a batch freezer may not work when processed in a PacoJet®.

Combine phases slowly

When emulsifying two liquids, begin slowly, adding just a small amount of the dispersion phase into the continuous phase and mixing thoroughly before adding more.

Adding all of the dispersion phase at once or too quickly can allow for large droplets of the dispersion phase to avoid being assimilated into the continuous phase. They will find each other and join together. The emulsion will reverse, with portions of the continuous phase floating in the dispersion phase.  By whisking as you add small amounts of the dispersion phase, you create more and more small droplets that disperse easily and remain dispersed, and these existing droplets will help the dispersion phase integrate with the continuous phase.

For some cake recipes, it can take up to 15 minutes of careful mixing to create a properly emulsified batter.

Temperature

An obvious example of disrespecting temperature protocol is adding cold eggs into a creamed mixture of room-temperature butter and sugar. The butter seizes immediately into tiny, distinct pieces, resulting in a curdled appearance. We can see this even more clearly when cool melted chocolate is added to a cold batter or whipped cream. The cocoa butter in the chocolate hardens instantly, creating a “chocolate chip” version of the product, but not in a desirable way.

In sauces, allowing the mixture to become too cold will harden the fats and cause them to form sharp-edged particles that further degrade the emulsion. If the mixture becomes too hot, the particles move rapidly, collide, and coalesce, thereby breaking the emulsion.

Shear

While good homogenization can be achieved by hand with a whisk or spatula, for best results, a food processor, PacoJet®, blender or hand blender is necessary. The rapidly spinning blades of these machines will break up droplets much more effectively, and the small amount of heat generated by the friction can help the emulsification process by keeping the fat liquid.

Can You Fix a Broken Emulsion?

While it is far better to carefully build and maintain a stable emulsion than to attempt culinary first aid on a curdled mess, it is possible in some cases to bring an emulsion back from the brink of disaster or even fix a mixture that appears to be past the point of no return. Pay attention while mixing and stop before tragedy strikes to ensure the easiest path back to homogenization.

For cake, cookie and tuile batters that start to appear curdled, stop adding liquid and let the batter mix, ideally using a machine rather than by hand, before adding more liquid. If the culprit was likely cold eggs, you can gently heat the batter with a kitchen torch or over a water bath, whisking or mixing until smooth, then proceed with warmer eggs or other liquid.

Adding a small portion of a cake or tuile recipe’s flour along with the eggs can prevent the batter’s emulsion from breaking. The flour acts as a stabilizer. Note that adding flour to a poorly emulsified batter may improve its appearance, but it will not repair the emulsion on a molecular level, and any significant additional mixing once all the flour has been added can create a tough, rather than tender, cake.

For buttercreams and ganaches, temperature can be the key to getting fat and liquid to get along again. Often, you’ll know what went wrong – the cream was too hot, the butter was added too soon or too late – and fixing it is a matter of bringing the mixture back from the extreme end of the temperature spectrum. Sometimes, it can be difficult to determine what the problem is. In this case, it is best to just choose a route and proceed with confidence – you’ve little to lose at this point.

For buttercreams, Shirley O. Corriher recommends whipping the butter, then gradually folding finished meringue into it, as you would with a mousse. Egg white foams, such as meringues, contain no emulsifiers, and this can make creating a nice emulsion with the butter tricky. By reversing the usual method, Corriher removes some of the anxiety from the process. Note that she also advocates replacing a small amount of the butter with shortening containing emulsifiers.

Step up your homogenization

A boost from something with a motor can be the key to a successfully emulsified mixture. If your whisk or spatula doesn’t seem to be doing the job, consider a burr mixer or food processor if it seems appropriate. Proceed with caution to avoid over-mixing or adding additional air.

High-speed shearing is what’s behind the trending tip to burr mix your buttercream for better color. The whirring blades break the color particles down into smaller droplets, increasing their coverage and helping them mingle with the fat in the frosting. In this case, removing air is the downside, and this method should be used strategically.

Anglaise and Other Egg-Based Sauces

Overcooking an egg-based sauce like anglaise results in coagulated egg yolks and a curdled appearance. While it’s possible to restore the sauce’s smooth appearance, it will still taste like cooked eggs.

Ice cream

Ice cream is a delicate product; many aspects of its formula can lead to an icy, grainy result if not calculated carefully. Tiny but detectable bits of fat in your frozen product are a good sign that emulsification is at the heart of the issue. In these cases, melting the ice cream and then homogenizing it by mechanical means before chilling and re-processing it can save the product. Ensuring the mix is properly emulsified from the start is far easier and less detrimental. Many chefs recommend homogenizing an ice cream base twice: burr mix the strained base once it is off the heat, and burr mix the chilled base once more before processing it in your machine. High-end batch freezers will often do this for you.

Check the recipe

Once we are at the emulsifying stage, it is usually too late to make changes, but analyzing the recipe can be a part of the post-mortem troubleshooting process. Check for typos and math errors and beware of inaccurate measurements!

Trivia

Egg yolks are such fabulous emulsifiers that the word lecithin comes from the Greek word lekithos, which means egg yolk.

(This article appeared in the Summer 32 issue of Pastry Arts Magazine)