Whipped cream was made for centuries before the mixer was invented. :)
You can do it with simply a balloon whisk. Things that may help though:
- Very cold cream (not freezing)
- Very cold bowl and whisk (put them in the freezer for 20 minutes prior to using)
- Copper bowl
The process is simply to start slow until you see bubbles form, then speed up until you see the whisk begin to leave trails in the cream, then go full speed ahead until just before it starts to look soft and billowy. At this point you can add your sugar and continue whipping until thickens and firms up to form soft peaks.
Advice: Buy a hand-mixer at least! :)
Update - Yes you can whip it with a stick blender. I would be careful to avoid over- whipping with this method though. It might be easy to over-do it, and you'll start to make butter.
A foam is just a liquid with plenty of air incorporated into it. You can incorporate air into any liquid; in order to be able to create an actual foam, however, you need to be able to incorporate the air faster than it escapes.
What makes a liquid able to hold the air you're incorporating (and hence form a foam) is a foam stabilizer, also commonly called an emulsifier1. I know of no specific taxonomy of stabilizers, but the vast majority are hydrocolloids AKA gelling agents and belong to some family of protein.
- Agar, carrageenan, alginate, xanthan, and pectin are all types of polysaccharide;
- Lecithin is mostly a random collection of phospholipids;
- Gelatin is denatured collagen, i.e. animal protein;
- Whey protein is the prevalent protein in dairy products;
And so on. Really almost any emulsifier will do. Basically everything in your list either is, or contains, one of the the additives mentioned above:
- Chocolate is almost always emulsified with soy lecithin;
- Eggs contain high amounts of lecithin;
- Milk and cream contain whey protein;
- Most "supermarket cream" also has emulsifiers like carrageenan already in it.
...you get the picture, I hope. The most basic answer I can give to this is that if you want to make a foam, you need to either use something that's already an emulsion (milk, butter, chocolate, etc.) or use an emulsifier/stabilizer additive (such as gelatin, lecithin, etc.)
If you want a relatively complete list of all of the food additives that qualify, you'll want to look at the E number, and specifically E400-499 (thickeners, stabilizers, emulsifiers).
1. As commenter Erik very correctly points out, an emulsifier is not the same thing as a foam stabilizer. However, by convention, the terms seem to be used interchangeably all over the place, to the extent that I get blank looks when I refer to a "stabilizer" as opposed to "emulsifier". So, know the difference, but don't get too hung up on it.
Best Answer
There is no single, universal technique for making random food "fluffy". And you may have to live with significant changes in the recipe and in the final results if you try it.
Classically, you have three types of foams. One is fat-based, the other is protein-based, the third depends on sudden gas production/dissolving.
The fat-based foam is only possible in liquids which are an emulsion of fat in water, and only functions within a certain range of fat/water, a favorable temperature range, and a proper size of the fat globules. This is what whipped cream is. Besides cream, you can whip that way a few other things such as ganache or mayonnaise (although mayonnaise is a bit more complicated, since it also has protein). It is almost impossible to make at home an emulsion which will behave that way, you may succeed with lecithine and very good equipment (a lab-style homogenizer will be preferable over blenders and other kitchen staples), and you will be very limited in the ingredients you use.
The protein-based foam happens when proteins link. This is also possible with only a few ingredients in the kitchen, most notably egg whites, aquafaba, and, under the right conditions, milk (that's what cappuchino wands do). It is even more finicky than fat-based foam.
The third one is the (more-or-less sudden) release of gas. This is e.g. how beer foam happens. They are always very short-lived for liquids, although in principle a sponge cake and similar baked goods are a batter that has been set into this bubbled-up state by baking.
None of the three types above are applicable to a random liquid or sauce. They all require that you start with a known ingredient that creates foams, and whip it under the proper conditions, with the least amount of additions.
A fourth, more modern way, is to try forcing a gas into the liquid from outside. This is how soda stream works, or whipped cream siphons. This can in principle work with a wide variety of liquids, but you have to do quite some food engineering before the resulting texture is acceptable. Most liquids won't hold the foam as-is, if they whip at all, so you have to add a binding agent.
So, if you want to really make a random sauce into a foam, the way to do it will be to purchase a siphon (don't forget to invest into enough charging cartridges, you will need a lot for your experimentation) and a variety of gums and other binding agents. Then you will have to experiment to determine the proper binding agent (and the proper amount of it) for your sauce. Since you probably don't want to run many hundreds of experiments per sauce, it is advisable that you also get the proper literature on the functioning of binders, and gain some hands-on experience by first following existing, optimized recipes for foams. After that, you can start designing your own recipes, and will probably get away with a dozen or two of experimental runs per sauce, depending on your level of experience and how exact your expectations of the outcome are.