Hi Elena, these days instant yeast and active dry yeast are produced in a very similar manner and are essentially interchangeable, however there are some circumstances where active dry yeast doesn't activate as well (when using cool water, for example, in an overnight starter). In this type of situation I usually recommend activating the active dry yeast in a small portion of the water called for, and making this liquid lukewarm. Once the yeast activates, you can add it to the remaining (cool) water and flour. 

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