Foams are one of the techniques most associated with modernist cooking. They are easy to make, very versatile, and fun to use and eat. Foams have been around traditional cooking for a very long time and include whipped cream, head on beers, and even bread dough.
At the most basic level, foams are a structure that traps air in bubbles. Foams are similar in this way to an emulsion, which is when a liquid traps fat in a structure, or fat traps liquids in a structure.
The structure can be made from a variety of things such as proteins, water, or fat. The texture of the foam is determined by the size of the bubbles and how much liquid is in the foam. Some foams are considered "set" foams, which means the structure has been solidified, such as when baking bread dough or a souffle.
The first use of culinary foams dates back to the 1700's when both sweet and savory souffles were created. The name souffle literally translates to "puffed up", which is a description of the dish and the soft matter which is neither flowing nor completely solid. The use of foams evolved to meringues and eventually the cream that is put in many gourmet beverages today.
In the world of molecular gastronomy, foams have evolved into a completely new cooking technique as well. Much of the change in how foams are used and prepared can be credited to Spanish chef Ferran Adr?a. In his efforts to enhance the flavor of food, Adr?a eliminated the use of cream or eggs in his foams. Instead, he combined various ingredients with air.
Culinary foams are often created with usual flavors taken from stock, fruit juices, vegetable purees and even soups. These are combined with stabilizing agents to prevent breakdown later on. Stabilizers range from natural plant and animal derivatives. Examples of commonly used stabilizers are agar agar and lecithin. Depending on what is being made, fats and egg whites may also be used.
Air is then introduced into these through a mechanical force in the form of whipping. Foams made with the use of a hand held immersion blender results in a delicate froth similar to that found in cappuccino. On the other hand those made with the use of a special cream whipper called a siphon results in espuma or air, which is dense foam comparable to mousse.
In the same way that traditional foams can be made either sweet or savory, so can modern cuisine foams. They can also be served in a range of temperatures from cold to hot.
Like many other molecular gastronomy techniques foam serves a number of purposes that all point to giving its audience a better dining experience. Flavor is one of the most important functions that foam carries in the kitchen. It allows cooks to incorporate various tastes into dishes being cooked without changing physical makeup. Foam can simply be added on top of a completed dish and it will deliver the desired flavor.
Without any doubt, culinary foams also play a large role in the way a dish looks when it is served. Long before the advent of modern cooking, foams had already served to make dishes look much more appetizing. With the use of new approaches and equipment in creating these airy substances, the options for creating enticing dishes are widened.
One of the things that can make dining more enjoyable is the experience of new things. Foams make it possible for diners to feel different textures in their mouth. This is especially true when it is combined with other foods that present other textures. It also allows for the use of unorthodox cooking methods such as the formation of sauces and even warm foams.
On a more industrial level, the production of foams with the use of a siphon makes it possible to store these substances longer. Modern cuisine foams have an extended shelf life and are not susceptible to absorbing smell and taste from other foods due to storage options. This means better tasting and fresher dishes will be served to diners.
Whether they are called bubbles, airs, meringues, espumas, puffs, or froths, all foams share certain characteristics. Similar to gels, these characteristics lie on a spectrum.
The texture of a foam ranges from fine to coarse and refers to the size and uniformness of the bubbles.
A foam with smaller, very uniform bubbles is considered fine. Whipped cream is an example of a fine foam. A foam with larger and less uniform bubbles is considered coarse. Some examples of coarse foams are latte froth, airs, and the head on light beer.
The wetness of a foam refers to the amount of liquid that is in the structure of the bubbles. Usually, the coarser a foam the dryer it is.
Dry foams are mainly air and can be very light. The bubbles are typically larger and their flavor is diluted due to the lack of liquid. Most very dry foams are referred to as "airs".
Wet foams have much more liquid in their structure. They can range from light to dense foams. They are usually fine foams, rather than coarse foams. Most commonly known foams are wet foams such as whipped cream and milkshake froth.
Foams can range from very light, such as airs, to very dense, mousse-like foams similar to whipped cream. The density depends on the texture and wetness of a foam. The finer the bubbles are and the wetter the foam is, the denser it becomes.
There are different names for types of foams. Some of these are interchangeable and none of the definitions are set in stone. To understand what people are talking about regarding foams, it's important that you learn the characteristics associated with the following names.
Typically a dry, coarse foam that is mainly made up of air. Strongly flavored liquids should be used in airs because they have such a small amount of liquid.
Dense foams refer to thicker, fine, wet foams. They usually have smaller bubbles. Whip cream is a good example of a dense foam.
Light foams lie somewhere in between airs and dense foams. They are finer and wetter than airs but not as thick as dense foams.
Like airs, bubbles are coarse foams but they tend to have more liquid in them than airs do and are made up of larger bubbles. They usually resemble common bubbles like those created by soap or shampoo.
Froths are usually wet but coarse foams. They are named after the froth that is often on the top of a milkshake or latte.
Set foams have had their structure solidified, often through heating or dehydrating. A loaf of bread and a baked souffle are examples.
"Espuma" is the Spanish word for foam and they are usually dense foams. They are always created by a whipping siphon and usually served hot.
Meringues and puffs are lighter foams that are often baked or dehydrated to set their structure.
Foams are created primarily by trapping air or gas bubbles in either a liquid or solid substance while allowing both of these to become stable. As mentioned earlier, a mechanical force assists with the introduction of air into the chosen substance.
During the process of creating foam, the mechanical force must be greater than the ability of the substance to breakdown in order to increase the surface area. This explains the need for very quick arm movements or the use of electric powered kitchen tools to expand the substance used.
Aside from the presence of mechanical work, there is also a need for the addition of a stabilizer which will work as a surfactant. This will coat the molecules and lessen the surface tension, allowing the molecules to adhere to each other more easily. Without a surfactant the liquid in the walls of the bubble pull down and the air inside the bubbles move up because of differing densities. This creates a tension which will weaken the walls causing the bubbles to pop and the foam to collapse.
The adherence of molecules to each other is characterized by groupings of three. In between the groups of threes, a network of interconnected films known as lamellae intersects at all edges. Once stabilized these intersecting films form a 120 angle. Such properties make way for thickened film and finer foam due to the stability of the molecules. It is also the same properties which allow these substances to stand firm and withstand breakdown. Foams are also classified under colloids owing to the presence of dispersed solid or liquid particles throughout.
In order for a foam to last more than a few seconds it needs to be stabilized. There are many ways to stabilize a foam, often by thickening or gelling the liquid.
For best foaming action be sure to pick liquids that are thin and watery and do not contain many particles. If you want to make a foam from a thicker sauce you can try watering it down until it becomes thinner and running it through a chinois if there are larger particles in it.
One of the simplest ways to create a foam is to combine a liquid with a thickening ingredient, such as xanthan gum. Then you introduce air into it, usually through whipping, blending, or using a whipping siphon. This usually results in a coarse, wet foam that is on the lighter side.
Xanthan gum is usually added in a 0.2% to 0.8% ratio, depending on the density of foam desired.
Similar to thickened liquid foams, stabilized foams combine a stabilizer such as lecithin or Versawhip with the liquid. The resulting foam tends to be a little finer than thickened liquid foams. These can usually be made with most of the foaming equipment listed in this article.
Using traditional stabilizing agents like egg white, cream, and sugar are also effective. Many of the things in those ingredients that stabilize the foam have been isolated and are sold as separate ingredients, such as lecithin. These are also incorporated into other modernist ingredients such as Versawhip.
A ratio of 0.5% to 1.0% is commonly used for Versawhip. Lecithin is used at a 0.25% to 1.0% ratio. Xanthan gum can also be added for thickening at 0.1% to 0.5%.
An effective way to create thicker foams is by using gels and fluid gels. You first turn the liquid you want to foam into a gel. Often times agar agar, iota carrageenan, gelatin, or methylcellulose are used to create the gel, or fluid gel. Depending on the ingredient, the gel can be whipped or put in a whipping siphon to create a foam. These foams have a range of textures and densities depending on the fluid gel used.
Agar fluid gels are usually made with a 0.25% to 1.0% ratio. Gelatin is used with a 0.4% to 1.7%. Xanthan gum can also be added to the above ingredients to thicken the foam, typically in a 0.1% to 0.4% ratio.
There are many tools you can use to create foams and each one results in a slightly different texture. The purpose of all the tools is to introduce air into the liquid you are foaming. For tools such as whisks and immersion blenders you want to make sure part of the tool is out of the liquid so it will carry air into the foam.
Whisks are a great way to create dense foams as well as some lighter foams. Manual whisks can get the job done but using an electric whisk attachment greatly speeds up the process and tends to make finer foams. The whisk attachment can be on an immersion blender or a standing mixer.
The whipping siphon is an awesome tool for making foams of all kinds. It is a container you fill with liquid and then pressurize with NO2 or occasionally CO2. They are very effective at creating foams and also help in the storage of liquids you will be foaming over time.
Mixers without a whisk attachment can also be used. They can create lighter foams very efficiently.
A milk frother is an inexpensive tool that is used to create foam for cappuccinos or lattes. When it used with modernist ingredients it can create similar foams from other liquids. Aerolatte brand frothers are usually under $20.
Immersion blenders are good at creating airs and other light foams. Ensuring part of the blade is out of the liquid is critical. A traditional standing blender will not work well for foaming because the blades are completely submerged.
An aquarium pump or bubbler is one of the more unusual ways to create foams. It works well for creating large bubbles, similar to soap bubbles. Tetra Whisper brand pumps can typically be found for under $10.
Light foams can be airy, coarse foams or wet, fine foams. They are also the easiest to make without additional kitchen equipment like a whipping siphon or standing mixer. You can make light foams in a few different ways but either an immersion blender or electric whisk works well, as do milk frothers or aquarium bubblers for specific types of foams.
To make a light foam you combine the liquid you want to foam with the foaming agent. For light foams the foaming agent is typically lecithin, sometimes with some xanthan gum added to create wetter froths.
Once the foaming agent has been incorporated you add air to the liquid through whipping or blending. If you are using an immersion blender you want to keep half of the blade out of the liquid so the maximum amount of air will be introduced.
Depending on the liquid and foaming agents used, the light foam will last for 30 to 60 minutes. However, it will lose body the longer it sits. You can spoon the light foam directly onto a dish or freeze it for a cold, ethereal treat.
At the dryer end of the spectrum, most airs use 0.25% to 1.0% lecithin, though the specific amount isn't as important as with many other techniques.
For wetter foams, xanthan gum can be added at 0.1% to 0.4%. The more xanthan gum added, the wetter the foam will tend to be.
For bubbles, resembling soap bubbles, a typical ratio is 0.1% to 0.4% xanthan gum and 0.2% to 2.0% Versawhip or egg white powder.
Fluid gel foams are denser and much finer than light foams and airs. They are usually very wet and thick, with a texture similar to shaving cream. Fluid gel foams are best made with a whipping siphon.
To make a fluid gel foam, you first create a fluid gel. Some good gelling agents are agar, carrageenan, gelatin, or methylcellulose. Once the fluid gel is made, place it in a whipping siphon and charge it. For some gels, like gelatin gels, you need to refrigerate it for a few hours so it can set. Once it's set you can dispense the foam.
For a detailed look at gels and fluid gels please see the section on Gelling.
You can also add xanthan gum, typically at a 0.1 to 0.4% ratio, to change the texture of the foam. Other thickeners work as well. Different stabilizers also can change the textures of the foams and are often combined with the gelling agent. This includes egg white, Versawhip, lecithin and many others.
Whipped foams are dense, wet foams such as whipped cream or meringues. Whipped foams are best made with a whipping siphon or a standing mixer with a whisk attachment. Some can be made with an electric hand mixer or a hand whisk but many of the thicker foams are just too dense for these tools. Whipped foams are created by dispersing a stabilizer into a liquid and then whipping it until peaks are formed. The stabilizer will help the foam stay together. In whipped cream the stabilizer is traditionally the fat in the cream and for meringues it is the proteins in the egg white.
For modernist foams you can also use methylcellulose, Versawhip, or other stabilizers. After you have created the whipped foam you have a few options of how to use it. You can serve it directly, like whipped cream on pie. You can also dehydrate the foam to create a meringue. Some foams can also be frozen. When serving it directly you can either spoon it out or use a pastry bag or a Ziploc bag with the corner cut off.
The amount of stabilizer you use depends on how stiff you want the foams, as well as the specific stabilizer you are using. In general you use Methocel F50 at a 1.0% to 2.0% with 0.1% to 0.3% xanthan gum. For Versawhip, a 0.5% to 2.0% ratio is ideal with 0.1% to 0.2% xanthan gum.