How much lecithin to make an air?

You’re right about lecithin (and other modern cuisine ingredients for that matter) being a potent ingredient for thickening, giving form and more. While you don’t really need to put a whole lot of it to get results, you still need the right ratio. I’m guessing that you might have put in a lot less lecithin than was needed to stabilize your air.

For airs the ratio of lecithin is 0.25% to 1.0% of the liquid’s weight. With 100 grams of liquid you can add 250 milligrams to 1 gram of lecithin. Try starting out with the smaller amount and increase it as needed. The great thing about airs is that it is not as sensitive as other modernist cooking techniques, so you don’t need an exact amount.