le Emulsioni in cucina. Cosa sono, tipologie, come farle, gli emulsionanti

Science in the Kitchen: Emulsions. What they are and how to make them

Cooking is an art that thrives on creativity, tradition and innovation. However, behind every delicious dish there is also a complex dance of scientific principles. From baking to fermentation, from leavening to emulsion formation, science permeates every aspect of our daily culinary preparations.

In this article we will explore one of these scientific wonders: emulsions. Often overlooked in their complexity, emulsions are the basis of many of our favorite sauces, aromatic vinaigrettes, and sumptuous creams. Behind their apparent simplicity lies a balance made up of chemical reactions.

Through this journey into the science of emulsions, we will discover how emulsifying agents work in harmony with liquids, fat-based and water-based, to create and maintain stable these valuable blends of oils and waters.

Get ready to immerse yourself in the world of emulsions in the kitchen, where manual skills and science meet to satisfy not only the palate, but also the curious mind of those of you who love to explore the secrets of gastronomy.

What is an emulsion?

What all emulsions have in common is the presence of a fatty and a water-based food. We know that two liquids mix evenly with each other if they are water-based, such as iced tea and coffee (yuck) or if they are fat-based, such as butter and oil. In contrast, if we try to put water and oil in a glass these will not mix. They will be arranged in two “phases,” and the thicker one will settle to the bottom.

Emulsion is the product of forcing; it succeeds to some extent in making foods that by their very nature are not related mix together.

How is it possible to do this? You don’t need to be a master chef equipped with a thousand technological gizmos, and at the end of the article you will find some easy recipes you can make in your own kitchens to look great at your next dinner party with friends!

It may sound curious, but we deal with emulsions much more often than we think. The most popular examples of emulsion in cooking are:

  • Mayonnaise: emulsion of oil and lemon-or vinegar-to which egg yolk is added to thicken
  • La
    vinaigrette
    : a dressing for salads or vegetables, made from oil and vinegar
  • La
    citronette
    : made with oil and lemon or orange juice, perfect for raw or cooked fish dishes, but also for chicken

Other less suspicious examples include butter, obtained by mechanical agitation from cream, and also Nutella, in which we find oil and skim milk, as well as cocoa and hazelnuts.

But emulsions don’t just crowd the refrigerator and supermarket counters. In fact, they are used in many industries, such as pharmaceuticals and cosmetics.

How many types of emulsion are there?

To make an emulsion, as we have said, you need a fatty and a watery element. Of course there will also be other substances, flavors, aromas and molecules, but chemically that is the basis. To define emulsions, we must now give the right names to the phases that are to be mixed in some way, which are:

  • Continuous phase: this is the ingredient normally present in the greatest quantity, whose components are continuous with each other because they are more abundant
  • Dispersed phase: this is the ingredient that disperses within the continuous phase, forming small droplets that swim within it. They do not touch each other if the emulsion is stable

Butter contains more fat than water, so it is said to be awater-in-oil” (W/O) emulsion, suggesting how the fat part, which for simplicity is always referred to as oil, is present in greater quantities. Conversely, foods such as cream, milk, salad dressings, mayonnaise and creams are oil-in-water” (O/W) emulsions. Within cream, for example, the amount of fat varies from 10 percent to 40 percent, the rest being aqueous solution.

We could stop here and that would be enough, but why deprive ourselves of the beauty of discovering that there are also multiple emulsion systems such as oil-in-water-in-oil (o/w/o) and water-in-oil-in-water (w/o/w)? The latter, for example, consists of water droplets dispersed in larger oil droplets that are still dispersed in a continuous aqueous phase.

These emulsions have advantages exploited in many applications such as controlling the release of a substance, reducing the overall fat content in a product or isolating one substance from another with which it would normally react.

Types of emulsions: water-in-oil, oil-in-oil, water-in-oil, oil-in-oil

The science of emulsions

Thus, we defined that emulsions are systems consisting of ingredients, phases, that are not related to each other, one of which is dispersed into the other in the form of droplets. But how is it done? How do you mix two substances that are not related? The simplest method of obtaining an emulsionis–mechanical agitation.

That’s right, elbow grease and rudimentary tools are in themselves enough to make the first experiments at home. We see this in all the videos on social media featuring homemade mayonnaise recipes using an immersion blender or hand whisk. Whatever instrument is available, on the physical level little changes: we are mechanically forcing this union. And it is perfectly fine if we have to consume these foods in the short term, the final effect will work.

Tension

In this precarious and unstable balance, there is a force that comes into play: the interfacial tension of the substances that make up the emulsion. A high tension is created between two liquids such as water and oil, given the fact that fats are nonpolar substances and water, on the other hand, is polar.

By their nature they would stand on the other side of the world from each other. No matter how mechanically we force their union…

How long can this balance last?

Physical forcing will not erase their incompatibilities, so over time the two phases will tend to separate. If you have made vinaigrette at home you may have noticed that once you sprinkle the salad with dressing, the components tend to separate quickly. It can be seen by eye!

How can we decrease this tension and make our emulsions last longer?

Emulsifiers

There are molecules with special properties that can do just that. They happen to be called emulsifiers, or surfactants. Their molecules consist of a polar head and an apolar tail. In other words, a water-like part, the polar part, and an oil-like part, the nonpolar part, coexist in the same molecule. We know well that similar compounds mix well, so we can imagine that this is exactly what happens. One part of the emulsifier binds to the water, the other part to the oil: in this way it manages to keep the two phases distant but … joined together, in good balance. It reduces this interface tension because it forms a film, a protective layer, around the droplets of the dispersed phase.

The action of emulsifiers to maintain emulsions longer

There are many foods in the kitchen that act as emulsifiers: mustard and potato starch, or corn starch, egg yolk are good examples. Isinglass, whey protein, and milk caseins are frequently used in the food industry, as well as starches.

In short, in the absence of surfactants the system over time tends to revert to its more “natural” configuration, separating. With the presence of an emulsifier, this process is greatly limited. Over time, however, stability will be equally affected. Although much more slowly, the two phases will tend to separate. We notice this effect in jars of peanut butter or Nutella abandoned in cupboards for months: a layer of oil will come off the surface.

The stability of emulsions

Several factors can affect the stability of emulsions, and it can occur in several ways. Influencing factors include, for example, temperature, whose increase corresponds to a higher rate of phase separation, from pH and the presence of salts.

When the phases separate what happens at the microscopic level is that the droplets of the dispersed phase begin to come together, forming progressively larger droplets. If these are lighter than the continuous phase, then they will go upward to form a smooth, firm surface layer. There are at least three different ways in which this can happen:

      • droplets may remain very small and detached from each other but come together all close together and rise to the surface
      • the droplets fuse together, gradually becoming larger and then rising to the surface

When one hears of cream by influx, one is referring precisely to the natural process by which the fat part of milk separates from the watery phase, rising to the surface, and then being collected and used in cooking.

Emulsions in cooking: three recipes to try

After all this theory we must be hungry, so it’s time to get our hands in the dough!

I leave you with recipes for three emulsions to try at home, which you can make using a hand whisk, electric whisk or immersion blender. If you have a small container with a good stopper, even a good shaker will do! I made butter at home with a plastic bottle and ten minutes of samba in the living room.

Vinaigrette

  • 2/3 oil
  • 1/3 wine vinegar or balsamic vinegar
  • 1 pinch of salt

Citronette

  • 2/3 oil
  • 1/3 lemon or other citrus fruit
  • 1 pinch of salt

In any of these preparations you can add pepper, herbs such as oregano, parsley and rosemary. And if you like try adding a little emulsifier, such as mustard, to observe the difference in separation times!

Bernese Sauce

  • 50g melted butter
  • 25 ml white wine vinegar
  • 1 yolk
  • cayenne pepper
  • 1 teaspoon tarragon
  • peppercorns
  • halls
  • lemon juice to taste.
  1. Finely chop tarragon, if fresh, and dry it with a napkin;
  2. We put the vinegar, scallions and half the tarragon, along with a little salt and peppercorns, in a steel saucepan. We turn it on and let it reduce to just over half;
  3. We remove from the heat, strain and let the flavored water cool;
  4. In a saucepan, we begin whipping the egg yolks with electric whisks, incorporating the vinegar and shallot infusion in a trickle;
  5. When it starts to become frothy, put it in a water bath in already hot water and continue whipping. Be careful not to exceed 60°C or the egg will coagulate, disassembling our sauce;
  6. Once the sauce is well whipped, we also add the melted butter in a trickle, a little at a time, working until the mixture has reached a smooth, even consistency;
  7. We then transfer the sauce to a bowl, add pepper and top with the leftover tarragon and a few drops of lemon.

Sources

D.J. McClements. Food Emulsions: Principles, Practices, and Techniques, Third Edition. Taylor & Francis Group, 2016.

S.M. Jafari and D.J. McClements. Nanoemulsions Formulation, Applications, and Characterization. Academic Press, 2018.

J.S. Komaiko and D.J. McClements. Formation of food-grade nanoemulsions using low-energy preparation methods: A review of available methods. Comprehensive Reviews in Food Science and Food Safety, 15(2):331-352, 2016.

Chemistry in the kitchen: emulsions, suspensions, gels. Patrizia dall’Antonia, Nadia Gasparinetti

https://bressanini-lescienze.blogautore.espresso.repubblica.it/2010/11/09/emulsioni/

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