What’s the purpose of lecithin? Does it make the chocolate thicker or thinner?

The easy one first. It makes chocolate thinner generally speaking. The caveat there is if you already have a chocolate with a high(er) level of cocoa butter, and/or lower level of water (there is always some) and you chocolate is already pretty thin, then it probably isn’t going to do much for viscosity. And now I am going to cheat. I’ve answered this a couple times in different ways. So I am going to refer you back to those Ask the Alchemist. But I’ll quote pieces from them here.

Ask the Alchemist 92

"..... With it in, you may bind water that would normally evaporate. But if it does not give you trouble, then why fix it? Also, (per the thread mentioned) it does act as an emulsifier…just with ingredients you don’t expect. Most people think of oil and water, but having two functional groups (a positive and negative if you like to think of it that way), allows it to form ‘bubble’ encapsulations called micelles, but instead of water being in them, they have a sugar molecule in the center and triglycerides (the cocoa butter) on the outside. In a way it is ‘removing’ some of the free solids in the chocolate, and the result is a more fluid, less viscous chocolate. So, it IS an emulsifier. Just not a water emulsifier."

Ask the Alchemist 39

“Lecithin is often described as an emulsifier. In chocolate, that is not really why it is used, but that property is used. What I mean by that is technically an emulsifier is used to bind somewhat equal parts of water and oil together. Like in a Caesar salad dressing. The egg is the emulsifier, and allows the oil and vinegar to bind together into an emulsion. In chocolate, as we all know by now, you don’t use water as it causes the chocolate to seize. But sometimes, either due to a lighter side roast, humidity or because certain ingredients (some sugars and milk powder) can easily absorb water, water does make it into the chocolate. The addition of a small amount of lecithin keeps the water from causing problems such as seizing or thickening the chocolate. But to repeat, it is an optional ingredient. I’m a big fan of ‘don’t fix what is not broken’. If your chocolate is not showing symptoms of moisture problems, and you like the chocolate, leave it be.

The other reason you may wish to use lecithin is actually for its emulsification properties. When baking, or cooking with homemade chocolate, more than once I found the recipe trying to separate, but the recipe was just fine with commercial chocolate. A little investigation led to the difference being a small amount of lecithin in the chocolate. The lecithin gives you just a little edge and leeway in having everything incorporate smoothly and evenly.”

So there you go. It is used as a viscosity modifier to make the chocolate thinner and an emulsifier.  It is completely optional if you find you don’t want to use it (some people are allergic to soy).

Send in your Ask the Alchemist questions to questions@chocolatealchemy.com