Many recipes recommend adding 1/4 teaspoon of cream of tartar to the chickpea brine to reach stiff peaks faster and obtain a more stable foam that deflates less quickly. It is the acidity of the cream of tartar that helps the chickpea brine foam. You could also replace the cream of tartar with the same amount of lemon juice or apple cider vinegar. However, you can easily make the aquafaba without an acidic ingredient and simply mix it a little longer.