Hydrate classification is an important step of the Bayer process both to achieve acceptable product quality and to maximize liquor productivity. In some of its plants, Rio Tinto Alcan operates gravity classifiers. They allow very efficient size classification and are cost effective. However, it is a challenge to consistently keep high underflow solids concentration especially as tanks age between turnarounds. Flow behavior shifts from mass flow to preferential flow and eventually to funnel flow as more hydrate accumulates in the tank. This generally results in reduction of the underflow solids concentration, recirculating more spent liquor into the precipitation circuit and thereby reducing liquor productivity. Over the last few years, Rio Tinto Alcan has addressed this constraint with the development of the HyDensTM hydrate solution. The main benefit of this new technology is to increase productivity via withdrawal of higher density hydrate. This paper will present milestones in the development and validation of this technology. It will describe its development at Rio Tinto Alcan Vaudreuil alumina refinery, Saguenay, Canada and its industrial application at the QAL alumina refinery located in Queensland, Australia. Finally, the benefits will be quantified.