If you've never tried homemade mayonnaise, you're in for a treat! The flavor is so much better than anything you can buy at the store and you avoid all that processing and the long list of non-food ingredients. In fact, you really only need three things to make mayonnaise - egg yolks, oil, and an acid.
Understanding a little bit about the science behind mayonnaise can help you see what's happening in each of the steps. Mayonnaise is an example of an emulsion. Basically, emulsions are just stable mixtures of two ingredients that don't normally mix, in this case oil and water. Even if you whisk oil and water until your arm falls off, they will separate after you stop. So what you need to do is find a way to get them to stay together - that's where emulsifiers come in.
In this mayonnaise recipe, the egg yolk and the mustard powder act as emulsifiers. Think of an emulsifier as a stabilizer. Egg yolks contain lecithin, which coats the surface of the oil droplets and prevents them from coming together again. This keeps them suspended in the water ingredients. The mustard powder with its very fine particles acts in a similar way.
Besides having emulsifiers, the other big key to making mayonnaise is to add the oil very, very slowly so it has time to disperse. That's why you'll see instructions to add it a drop at a time or in a very thin, threadlike stream. I bet the most common reason for not having an emulsion form when making mayonnaise is the oil being added too quickly! If this happens, all is not lost. Mix another egg yolk with about a teaspoon each of water and the acid you're using and slowly whisk the unsuccessful mayo (it's usually referred to as being "broken") into this.
One more thing before we get to the recipe - the egg yolk. Because mayonnaise is not cooked, use a fresh egg that you are reasonably sure is from a chicken that does not carry salmonella. If you don't raise your own eggs, talk to a farmer who does. Eat Wild and Local Harvest are two websites that can help you find people near you who raise food. The other reason you want a fresh egg is that lecithin breaks down as the egg ages and you want lots of lecithin to help your emulsion form!
Homemade Olive Oil Mayonnaise
1 cup of good quality extra virgin olive oil
1 T room temperature water
1 T lemon juice
1 room temperature egg yolk
1/4 tsp. salt
1/2 tsp. mustard powder
I use a food processor - regular blenders work and I know people who use immersion blenders with great success. I just have trouble holding the immersion blender in one hand while slowly streaming the oil with the other - it's a coordination problem! If you use a food processor, look at the lid and see if there is a tiny hole. Cuisinart is one brand that has a small cup insert in the lid that has a tiny hole in the bottom. This is so you can pour the oil into the cup and it will automatically stream into the mixture in a thin stream - very handy!
Continue until you have used all of the oil. Occasionally I'll have a great emulsion and still have about a quarter cup of oil left. I usually stop there and don't add the extra oil. It's already mayonnaise!
You can get creative with your own, homemade mayonnaise! Try adding chopped up herbs at the end or a spoonful of pesto. You can also play around with using different vinegars or wine instead of the lemon juice. We enjoy adding grated lemon peel and garlic to make a dipping sauce for artichokes.