Full Idea
An essence is not a property (or a cluster of properties) of the substance whose essence it is, ...because no property (no Aristotelian property) can be the cause of being of an actual individual substance.
Gist of Idea
Essences are not properties (since those can't cause individual substances)
Source
report of Aristotle (Metaphysics [c.324 BCE], ess) by Charlotte Witt - Substance and Essence in Aristotle Intro
Book Reference
Witt,Charlotte: 'Substance and Essence in Aristotle' [Cornell 1994], p.3
A Reaction
This is the third of Witt's three unorthodox theses, mainly in defence of individual essences in Aristotle. The first two seem to me to be correct, and the third one is interesting. I'm inclined to think that essences are powers, found below properties.