Ethanol shows a complex scenario of different crystalline phases in the temperature range between its glass transition at T(g) = 97 K and its melting point at T(m) = 159 K. Brillouin spectroscopy has revealed capable of observing and assessing acoustic phonon changes related to these phase transitions between different crystalline phases (either a plastic-crystal phase or different monoclinic phases). By combining this technique and calorimetric experimental data, we are able to corroborate the existence of at least two stable and two metastable (monoclinic) crystalline phases of pure ethanol.