Mayonnaise is some pretty magical stuff. Take two runny, liquidy ingredients—egg yolks and oil—combine them with a bit of mechanical action, and boom, thick, creamy, dippable, spreadable condiment at your disposal.
Occasionally you'll find a recipe for mayonnaise with a very high egg yolk to oil ratio, in which case the egg plays a role in the flavor of the final sauce. For the most part, however, the flavoring comes from the acid, the oil, the salt, and—if you're using it—the mustard and garlic. The egg yolk is there primarily for its chemical characteristics as well as to add some water for the oil to emulsify with (more on emulsions later).
So, I thought to myself, egg yolk's primarily water with a little bit of emulsifier. What's stopping you from using something completely different to form the base of mayonnaise?
Turns out there's nothing stopping you. There are a whole host of ways to make flavored mayonnaises without using an egg, and the great news for me during my Vegan Experience is that by taking out the egg, mayo becomes 100% vegan!
Physics of Mayo, Quick Recap
It's pretty simple, really. We all know that oil and water don't mix, right? It has to do with the way those tiny molecules are charged. Oil molecules are charged to like other oil, while water molecules are charged to like other water. Mix the two together and eventually all the water molecules will find each other and organize into one big group that then sinks to the bottom of the cup, no matter how thoroughly you mix the two to begin with.
To solve this dilemma and get everything nice and stable, you need the help of emulsifiers. With standard mayonnaise, that emulsifier comes in the form of lecithin, a phospholipid found in abundance in egg yolks. It has the property of being attracted to both oil and water. Look at mayo under a really big microscope and you'd see that it's made of tiny droplets of fat in which lecithin molecules have buried their oil-loving heads, leaving their water-loving tails sticking outwards. This allows the oil droplets and water to peacefully coexist.
Its thickness comes from the fact that lecithin-coated oil droplets don't slide around as easily as non-coated droplets, making the entire thing thicker. As for the color, that comes from the way light gets diffracted through the many many layers of oil and water. Imagine a ray of light as a stream of water coming out of a garden hose. With no disturbances, that stream is transparent—you can see right through it. Pass that stream of water through a very disturbing material—say, a mesh bag filled with gravel—and rather than staying as a distinct stream, it gets broken down into many tiny drops and comes out the other end with a completely different look, acquiring some level of opaqueness.
Egg-Less Mayo Experimentation
I made a quick video showing you how to make mayonnaise in two minutes or less using a hand blender. Using this method as a base, I tried making mayo using a number of different ingredients replacing the egg yolk.
The basic method is to stick your base along with some mustard, lemon juice, and (in this case) garlic into the bottom of a jar that just barely fits the business end of your immersion blender. After that, you top it up with oil, stick the blender in, and start whizzing, slowly pulling out the wand as you go. The vortex pulls oil down towards the base where it gets emulsified by the rapidly spinning blade.
The most neutral, natural-tasting mayo was a batch made with a bit of silken tofu replacing the egg yolks. Indeed, to me it tasted exactly like regular mayo. A small amount of well-cooked vegetables also works. Bean mayo, spinach mayo, artichoke mayo. Even a plain slice of white bread soaked in a tiny bit of water can form the base of the mayonnaise.
The tastiest one I made—the one which my non-vegan wife has been spreading on her bread instead of "real" mayo—was made with roasted eggplant. It gets a bit of spiciness and bitterness from the eggplant, sort of like very watered down (oiled down? mayoed down?) baba ghanoush.
I mixed mine with equal parts whole grain mustard and have it in a squeeze bottle in the fridge, ready to be applied generously at moment's notice.
"But hang on!" you must be saying. "What about the lecithin? How the heck are these veggie-based mayos staying emulsified?"
Very good question. The answer is that they aren't really. At least, they sort of aren't. See, semi-stable emulsions can form even in the absence of a good chemical emulsifier. Break down the oil and water droplets small enough and disperse them evenly enough and they'll stay that way for an awfully long time. Minutes, hours, even days, depending on their ratio and how well dispersed the droplets are.
After an overnight stay in the fridge or about an hour of sitting out on a plate, my eggplant mayo, for instance, will start to lose some body and take on a slightly greasy appearance. A quick re-blend tightens it back up, but an easier solution is just to add some extra lecithin to keep everybody happy. Soy-derived lecithin is readily available in granulated form. A tiny pinch added to the base before emulsifying gave my veg-based mayos the body and stability of even the tightest egg-based mayo.