The basic concept is “just add water. ” Just not too much…or too little.
It takes some trial and error to get the right amount of water to reconstitute freeze dried foods. Some foods (or ingredients) don’t restore to their original form. Recipes may need to change to account for reconstitution differences.
We have dedicated a part of our freeze dryer recipes to reconstituting the freeze dried ingredients used in them.
We also have a cheat sheet for freeze dried ingredients used in our recipes. It’s a quick reference to look up the right amount of water to reconstitute ingredients.